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..
-------------------------------------------------------------------
NOTE: This file is automatically generated by running clang-tblgen
-gen-opt-docs. Do not edit this file by hand!!
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=====================================
Clang command line argument reference
=====================================
.. contents::
:local:
Introduction
============
This page lists the command line arguments currently supported by the
GCC-compatible ``clang`` and ``clang++`` drivers.
.. program:: clang
.. option:: -B<prefix>, --prefix <arg>, --prefix=<arg>
Search $prefix/$triple-$file and $prefix$file for executables, libraries, includes, and data files used by the compiler. $prefix may or may not be a directory
.. option:: -F<arg>
Add directory to framework include search path
.. option:: -ObjC
Treat source input files as Objective-C inputs
.. program:: clang1
.. option:: -ObjC++
.. program:: clang
Treat source input files as Objective-C++ inputs
.. option:: -Qn, -fno-ident
Do not emit metadata containing compiler name and version
.. option:: -Qunused-arguments
Don't emit warning for unused driver arguments
.. option:: -Qy, -fident
Emit metadata containing compiler name and version
.. option:: -Wa,<arg>,<arg2>...
Pass the comma separated arguments in <arg> to the assembler
.. option:: -Wlarge-by-value-copy=<arg>
.. option:: -Xarch\_<arg1> <arg2>
.. program:: clang1
.. option:: -Xarch\_device <arg>
.. program:: clang
Pass <arg> to the CUDA/HIP device compilation
.. program:: clang2
.. option:: -Xarch\_host <arg>
.. program:: clang
Pass <arg> to the CUDA/HIP host compilation
.. option:: -Xcuda-fatbinary <arg>
Pass <arg> to fatbinary invocation
.. option:: -Xcuda-ptxas <arg>
Pass <arg> to the ptxas assembler
.. option:: -Xopenmp-target <arg>
Pass <arg> to the target offloading toolchain.
.. program:: clang1
.. option:: -Xopenmp-target=<triple> <arg>
.. program:: clang
Pass <arg> to the target offloading toolchain identified by <triple>.
.. option:: -Z<arg>
.. option:: -a<arg>, --profile-blocks
.. option:: -all\_load
.. option:: -allowable\_client <arg>
.. option:: --analyze
Run the static analyzer
.. option:: --analyzer-no-default-checks
.. option:: --analyzer-output<arg>
Static analyzer report output format (html\|plist\|plist-multi-file\|plist-html\|sarif\|sarif-html\|text).
.. option:: -arch <arg>
.. program:: clang1
.. option:: -arch\_errors\_fatal
.. program:: clang
.. program:: clang2
.. option:: -arch\_only <arg>
.. program:: clang
.. option:: -arcmt-migrate-emit-errors
Emit ARC errors even if the migrator can fix them
.. option:: -arcmt-migrate-report-output <arg>
Output path for the plist report
.. option:: --autocomplete=<arg>
.. option:: -bind\_at\_load
.. option:: -bundle
.. program:: clang1
.. option:: -bundle\_loader <arg>
.. program:: clang
.. option:: -client\_name<arg>
.. option:: -compatibility\_version<arg>
.. option:: --config <arg>
Specifies configuration file
.. option:: --constant-cfstrings
.. option:: --cuda-compile-host-device
Compile CUDA code for both host and device (default). Has no effect on non-CUDA compilations.
.. option:: --cuda-device-only
Compile CUDA code for device only
.. option:: --cuda-host-only
Compile CUDA code for host only. Has no effect on non-CUDA compilations.
.. option:: --cuda-include-ptx=<arg>, --no-cuda-include-ptx=<arg>
Include PTX for the following GPU architecture (e.g. sm\_35) or 'all'. May be specified more than once.
.. option:: --cuda-noopt-device-debug, --no-cuda-noopt-device-debug
Enable device-side debug info generation. Disables ptxas optimizations.
.. option:: -cuid=<arg>
An ID for compilation unit, which should be the same for the same compilation unit but different for different compilation units. It is used to externalize device-side static variables for single source offloading languages CUDA and HIP so that they can be accessed by the host code of the same compilation unit.
.. option:: -current\_version<arg>
.. option:: -dead\_strip
.. option:: -dependency-dot <arg>
Filename to write DOT-formatted header dependencies to
.. option:: -dependency-file <arg>
Filename (or -) to write dependency output to
.. option:: -dsym-dir<dir>
Directory to output dSYM's (if any) to
.. option:: -dumpmachine
.. option:: -dumpversion
.. option:: --dyld-prefix=<arg>, --dyld-prefix <arg>
.. option:: -dylib\_file <arg>
.. option:: -dylinker
.. program:: clang1
.. option:: -dylinker\_install\_name<arg>
.. program:: clang
.. option:: -dynamic
.. option:: -dynamiclib
.. option:: -emit-ast
Emit Clang AST files for source inputs
.. option:: --emit-static-lib
Enable linker job to emit a static library.
.. option:: -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
Trivial automatic variable initialization to zero is only here for benchmarks, it'll eventually be removed, and I'm OK with that because I'm only using it to benchmark
.. option:: -exported\_symbols\_list <arg>
.. option:: -faligned-new=<arg>
.. option:: -ffixed-r19
Reserve register r19 (Hexagon only)
.. option:: -fgpu-flush-denormals-to-zero, -fcuda-flush-denormals-to-zero, -fno-gpu-flush-denormals-to-zero
Flush denormal floating point values to zero in CUDA/HIP device mode.
.. option:: -fheinous-gnu-extensions
.. option:: -flat\_namespace
.. option:: -fopenmp-targets=<arg1>,<arg2>...
Specify comma-separated list of triples OpenMP offloading targets to be supported
.. option:: -force\_cpusubtype\_ALL
.. program:: clang1
.. option:: -force\_flat\_namespace
.. program:: clang
.. program:: clang2
.. option:: -force\_load <arg>
.. program:: clang
.. option:: -framework <arg>
.. option:: -frtlib-add-rpath, -fno-rtlib-add-rpath
Add -rpath with architecture-specific resource directory to the linker flags
.. option:: -fsanitize-system-ignorelist=<arg>, -fsanitize-system-blacklist=<arg>
Path to system ignorelist file for sanitizers
.. option:: -fshow-skipped-includes
#include files may be "skipped" due to include guard optimization
or #pragma once. This flag makes -H show also such includes.
.. option:: -fsystem-module
Build this module as a system module. Only used with -emit-module
.. option:: -fuse-cuid=<arg>
Method to generate ID's for compilation units for single source offloading languages CUDA and HIP: 'hash' (ID's generated by hashing file path and command line options) \| 'random' (ID's generated as random numbers) \| 'none' (disabled). Default is 'hash'. This option will be overridden by option '-cuid=\[ID\]' if it is specified.
.. option:: --gcc-toolchain=<arg>, -gcc-toolchain <arg>
Search for GCC installation in the specified directory on targets which commonly use GCC. The directory usually contains 'lib{,32,64}/gcc{,-cross}/$triple' and 'include'. If specified, sysroot is skipped for GCC detection. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
.. option:: -gcodeview
Generate CodeView debug information
.. option:: -gcodeview-ghash, -gno-codeview-ghash
Emit type record hashes in a .debug$H section
.. option:: --gpu-instrument-lib=<arg>
Instrument device library for HIP, which is a LLVM bitcode containing \_\_cyg\_profile\_func\_enter and \_\_cyg\_profile\_func\_exit
.. option:: --gpu-max-threads-per-block=<arg>
Default max threads per block for kernel launch bounds for HIP
.. option:: -headerpad\_max\_install\_names<arg>
.. option:: -help, --help
Display available options
.. option:: --help-hidden
Display help for hidden options
.. option:: --hip-link
Link clang-offload-bundler bundles for HIP
.. option:: --hip-version=<arg>
HIP version in the format of major.minor.patch
.. option:: -ibuiltininc
Enable builtin #include directories even when -nostdinc is used before or after -ibuiltininc. Using -nobuiltininc after the option disables it
.. option:: -image\_base <arg>
.. option:: -index-header-map
Make the next included directory (-I or -F) an indexer header map
.. option:: -init <arg>
.. option:: -install\_name <arg>
.. option:: -interface-stub-version=<arg>
.. option:: -keep\_private\_externs
.. option:: -lazy\_framework <arg>
.. program:: clang1
.. option:: -lazy\_library <arg>
.. program:: clang
.. option:: -mbig-endian, -EB
.. option:: -mbranch-protection=<arg>
Enforce targets of indirect branches and function returns
.. option:: -menable-unsafe-fp-math
Allow unsafe floating-point math optimizations which may decrease precision
.. option:: -mharden-sls=<arg>
Select straight-line speculation hardening scope
.. option:: --migrate
Run the migrator
.. option:: -mios-simulator-version-min=<arg>, -miphonesimulator-version-min=<arg>
.. option:: -mlinker-version=<arg>
.. option:: -mlittle-endian, -EL
.. option:: -mllvm <arg>
Additional arguments to forward to LLVM's option processing
.. option:: -module-dependency-dir <arg>
Directory to dump module dependencies to
.. option:: -mtvos-simulator-version-min=<arg>, -mappletvsimulator-version-min=<arg>
.. option:: -multi\_module
.. option:: -multiply\_defined <arg>
.. program:: clang1
.. option:: -multiply\_defined\_unused <arg>
.. program:: clang
.. option:: -mwatchos-simulator-version-min=<arg>, -mwatchsimulator-version-min=<arg>
.. option:: --no-cuda-version-check
Don't error out if the detected version of the CUDA install is too low for the requested CUDA gpu architecture.
.. option:: -no-integrated-cpp, --no-integrated-cpp
.. option:: -no\_dead\_strip\_inits\_and\_terms
.. option:: -nobuiltininc
Disable builtin #include directories
.. option:: -nodefaultlibs
.. option:: -nofixprebinding
.. option:: -nogpuinc, -nocudainc
Do not add include paths for CUDA/HIP and do not include the default CUDA/HIP wrapper headers
.. option:: -nogpulib, -nocudalib
Do not link device library for CUDA/HIP device compilation
.. option:: -nolibc
.. option:: -nomultidefs
.. option:: -nopie, -no-pie
.. option:: -noprebind
.. option:: -noprofilelib
.. option:: -noseglinkedit
.. option:: -nostdinc, --no-standard-includes
.. program:: clang1
.. option:: -nostdinc++
.. program:: clang
Disable standard #include directories for the C++ standard library
.. option:: -nostdlib++
.. option:: -nostdlibinc
.. option:: -o<file>, --output <arg>, --output=<arg>
Write output to <file>
.. option:: -objcmt-atomic-property
Make migration to 'atomic' properties
.. option:: -objcmt-migrate-all
Enable migration to modern ObjC
.. option:: -objcmt-migrate-annotation
Enable migration to property and method annotations
.. option:: -objcmt-migrate-designated-init
Enable migration to infer NS\_DESIGNATED\_INITIALIZER for initializer methods
.. option:: -objcmt-migrate-instancetype
Enable migration to infer instancetype for method result type
.. option:: -objcmt-migrate-literals
Enable migration to modern ObjC literals
.. option:: -objcmt-migrate-ns-macros
Enable migration to NS\_ENUM/NS\_OPTIONS macros
.. option:: -objcmt-migrate-property
Enable migration to modern ObjC property
.. option:: -objcmt-migrate-property-dot-syntax
Enable migration of setter/getter messages to property-dot syntax
.. option:: -objcmt-migrate-protocol-conformance
Enable migration to add protocol conformance on classes
.. option:: -objcmt-migrate-readonly-property
Enable migration to modern ObjC readonly property
.. option:: -objcmt-migrate-readwrite-property
Enable migration to modern ObjC readwrite property
.. option:: -objcmt-migrate-subscripting
Enable migration to modern ObjC subscripting
.. option:: -objcmt-ns-nonatomic-iosonly
Enable migration to use NS\_NONATOMIC\_IOSONLY macro for setting property's 'atomic' attribute
.. option:: -objcmt-returns-innerpointer-property
Enable migration to annotate property with NS\_RETURNS\_INNER\_POINTER
.. option:: -objcmt-whitelist-dir-path=<arg>, -objcmt-white-list-dir-path=<arg>
Only modify files with a filename contained in the provided directory path
.. option:: -object
.. option:: --offload-arch=<arg>, --cuda-gpu-arch=<arg>, --no-offload-arch=<arg>
CUDA offloading device architecture (e.g. sm\_35), or HIP offloading target ID in the form of a device architecture followed by target ID features delimited by a colon. Each target ID feature is a pre-defined string followed by a plus or minus sign (e.g. gfx908:xnack+:sramecc-). May be specified more than once.
.. option:: -p, --profile
.. option:: -pagezero\_size<arg>
.. option:: -pg
Enable mcount instrumentation
.. option:: -pipe, --pipe
Use pipes between commands, when possible
.. option:: -prebind
.. program:: clang1
.. option:: -prebind\_all\_twolevel\_modules
.. program:: clang
.. option:: -preload
.. option:: --print-diagnostic-categories
.. option:: -print-effective-triple, --print-effective-triple
Print the effective target triple
.. option:: -print-file-name=<file>, --print-file-name=<file>, --print-file-name <arg>
Print the full library path of <file>
.. option:: -print-ivar-layout
Enable Objective-C Ivar layout bitmap print trace
.. option:: -print-libgcc-file-name, --print-libgcc-file-name
Print the library path for the currently used compiler runtime library ("libgcc.a" or "libclang\_rt.builtins.\*.a")
.. option:: -print-multi-directory, --print-multi-directory
.. option:: -print-multi-lib, --print-multi-lib
.. option:: -print-multiarch, --print-multiarch
Print the multiarch target triple
.. option:: -print-prog-name=<name>, --print-prog-name=<name>, --print-prog-name <arg>
Print the full program path of <name>
.. option:: -print-resource-dir, --print-resource-dir
Print the resource directory pathname
.. option:: -print-rocm-search-dirs, --print-rocm-search-dirs
Print the paths used for finding ROCm installation
.. option:: -print-runtime-dir, --print-runtime-dir
Print the directory pathname containing clangs runtime libraries
.. option:: -print-search-dirs, --print-search-dirs
Print the paths used for finding libraries and programs
.. option:: -print-target-triple, --print-target-triple
Print the normalized target triple
.. option:: -print-targets, --print-targets
Print the registered targets
.. option:: -private\_bundle
.. option:: -pthread, -no-pthread
Support POSIX threads in generated code
.. option:: -pthreads
.. option:: -read\_only\_relocs <arg>
.. option:: -relocatable-pch, --relocatable-pch
Whether to build a relocatable precompiled header
.. option:: -remap
.. option:: -rewrite-legacy-objc
Rewrite Legacy Objective-C source to C++
.. option:: -rtlib=<arg>, --rtlib=<arg>, --rtlib <arg>
Compiler runtime library to use
.. option:: -save-stats=<arg>, --save-stats=<arg>, -save-stats (equivalent to -save-stats=cwd), --save-stats (equivalent to -save-stats=cwd)
Save llvm statistics.
.. option:: -save-temps=<arg>, --save-temps=<arg>, -save-temps (equivalent to -save-temps=cwd), --save-temps (equivalent to -save-temps=cwd)
Save intermediate compilation results.
.. option:: -sectalign <arg1> <arg2> <arg3>
.. option:: -sectcreate <arg1> <arg2> <arg3>
.. option:: -sectobjectsymbols <arg1> <arg2>
.. option:: -sectorder <arg1> <arg2> <arg3>
.. option:: -seg1addr<arg>
.. option:: -seg\_addr\_table <arg>
.. program:: clang1
.. option:: -seg\_addr\_table\_filename <arg>
.. program:: clang
.. option:: -segaddr <arg1> <arg2>
.. option:: -segcreate <arg1> <arg2> <arg3>
.. option:: -seglinkedit
.. option:: -segprot <arg1> <arg2> <arg3>
.. option:: -segs\_read\_<arg>
.. program:: clang1
.. option:: -segs\_read\_only\_addr <arg>
.. program:: clang
.. program:: clang2
.. option:: -segs\_read\_write\_addr <arg>
.. program:: clang
.. option:: -serialize-diagnostics <arg>, --serialize-diagnostics <arg>
Serialize compiler diagnostics to a file
.. option:: -shared-libgcc
.. option:: -shared-libsan, -shared-libasan
Dynamically link the sanitizer runtime
.. option:: -single\_module
.. option:: -static-libgcc
.. option:: -static-libsan
Statically link the sanitizer runtime
.. option:: -static-libstdc++
.. option:: -static-openmp
Use the static host OpenMP runtime while linking.
.. option:: -std-default=<arg>
.. option:: -stdlib=<arg>, --stdlib=<arg>, --stdlib <arg>
C++ standard library to use
.. option:: -sub\_library<arg>
.. program:: clang1
.. option:: -sub\_umbrella<arg>
.. program:: clang
.. option:: --sysroot=<arg>, --sysroot <arg>
.. option:: --target-help
.. option:: --target=<arg>, -target <arg>
Generate code for the given target
.. option:: -time
Time individual commands
.. option:: -traditional, --traditional
.. option:: -traditional-cpp, --traditional-cpp
Enable some traditional CPP emulation
.. option:: -twolevel\_namespace
.. program:: clang1
.. option:: -twolevel\_namespace\_hints
.. program:: clang
.. option:: -umbrella <arg>
.. option:: -unexported\_symbols\_list <arg>
.. option:: -unwindlib=<arg>, --unwindlib=<arg>
Unwind library to use
.. option:: -v, --verbose
Show commands to run and use verbose output
.. option:: --verify-debug-info
Verify the binary representation of debug output
.. option:: --version
Print version information
.. option:: -w, --no-warnings
Suppress all warnings
.. option:: -weak-l<arg>
.. option:: -weak\_framework <arg>
.. program:: clang1
.. option:: -weak\_library <arg>
.. program:: clang
.. program:: clang2
.. option:: -weak\_reference\_mismatches <arg>
.. program:: clang
.. option:: -whatsloaded
.. option:: -why\_load, -whyload
.. option:: -working-directory<arg>, -working-directory=<arg>
Resolve file paths relative to the specified directory
.. option:: -x<language>, --language <arg>, --language=<arg>
Treat subsequent input files as having type <language>
.. option:: -y<arg>
Actions
=======
The action to perform on the input.
.. option:: -E, --preprocess
Only run the preprocessor
.. option:: -S, --assemble
Only run preprocess and compilation steps
.. option:: -c, --compile
Only run preprocess, compile, and assemble steps
.. option:: -emit-interface-stubs
Generate Interface Stub Files.
.. option:: -emit-llvm
Use the LLVM representation for assembler and object files
.. option:: -emit-merged-ifs
Generate Interface Stub Files, emit merged text not binary.
.. option:: -fsyntax-only
.. option:: -module-file-info
Provide information about a particular module file
.. option:: --precompile
Only precompile the input
.. option:: -rewrite-objc
Rewrite Objective-C source to C++
.. option:: -verify-pch
Load and verify that a pre-compiled header file is not stale
Compilation flags
=================
Flags controlling the behavior of Clang during compilation. These flags have
no effect during actions that do not perform compilation.
.. option:: -Xassembler <arg>
Pass <arg> to the assembler
.. option:: -Xclang <arg>
Pass <arg> to the clang compiler
.. option:: -ansi, --ansi
.. option:: -fc++-abi=<arg>
C++ ABI to use. This will override the target C++ ABI.
.. option:: -fclang-abi-compat=<version>
Attempt to match the ABI of Clang <version>
.. option:: -fcomment-block-commands=<arg>,<arg2>...
Treat each comma separated argument in <arg> as a documentation comment block command
.. option:: -fcomplete-member-pointers, -fno-complete-member-pointers
Require member pointer base types to be complete if they would be significant under the Microsoft ABI
.. option:: -fcrash-diagnostics-dir=<dir>
Put crash-report files in <dir>
.. option:: -fdeclspec, -fno-declspec
Allow \_\_declspec as a keyword
.. option:: -fdepfile-entry=<arg>
.. option:: -fdiagnostics-fixit-info, -fno-diagnostics-fixit-info
.. option:: -fdiagnostics-format=<arg>
.. option:: -fdiagnostics-parseable-fixits
Print fix-its in machine parseable form
.. option:: -fdiagnostics-print-source-range-info
Print source range spans in numeric form
.. option:: -fdiagnostics-show-category=<arg>
.. option:: -fdiscard-value-names, -fno-discard-value-names
Discard value names in LLVM IR
.. option:: -fexperimental-relative-c++-abi-vtables, -fno-experimental-relative-c++-abi-vtables
Use the experimental C++ class ABI for classes with virtual tables
.. option:: -fexperimental-strict-floating-point
Enables experimental strict floating point in LLVM.
.. option:: -ffine-grained-bitfield-accesses, -fno-fine-grained-bitfield-accesses
Use separate accesses for consecutive bitfield runs with legal widths and alignments.
.. option:: -fglobal-isel, -fexperimental-isel, -fno-global-isel
Enables the global instruction selector
.. option:: -finline-functions, -fno-inline-functions
Inline suitable functions
.. option:: -finline-hint-functions
Inline functions which are (explicitly or implicitly) marked inline
.. option:: -flegacy-pass-manager, -fno-experimental-new-pass-manager, -fno-legacy-pass-manager
Use the legacy pass manager in LLVM
.. option:: -fno-crash-diagnostics
Disable auto-generation of preprocessed source files and a script for reproduction during a clang crash
.. option:: -fno-sanitize-ignorelist, -fno-sanitize-blacklist
Don't use ignorelist file for sanitizers
.. option:: -fparse-all-comments
.. option:: -frecord-command-line, -fno-record-command-line, -frecord-gcc-switches
.. option:: -fsanitize-address-destructor=<arg>
Set destructor type used in ASan instrumentation
.. option:: -fsanitize-address-field-padding=<arg>
Level of field padding for AddressSanitizer
.. option:: -fsanitize-address-globals-dead-stripping
Enable linker dead stripping of globals in AddressSanitizer
.. option:: -fsanitize-address-poison-custom-array-cookie, -fno-sanitize-address-poison-custom-array-cookie
Enable poisoning array cookies when using custom operator new\[\] in AddressSanitizer
.. option:: -fsanitize-address-use-after-return=<mode>
Select the mode of detecting stack use-after-return in AddressSanitizer
.. option:: -fsanitize-address-use-after-scope, -fno-sanitize-address-use-after-scope
Enable use-after-scope detection in AddressSanitizer
.. option:: -fsanitize-address-use-odr-indicator, -fno-sanitize-address-use-odr-indicator
Enable ODR indicator globals to avoid false ODR violation reports in partially sanitized programs at the cost of an increase in binary size
.. option:: -fsanitize-cfi-canonical-jump-tables, -fno-sanitize-cfi-canonical-jump-tables
Make the jump table addresses canonical in the symbol table
.. option:: -fsanitize-cfi-cross-dso, -fno-sanitize-cfi-cross-dso
Enable control flow integrity (CFI) checks for cross-DSO calls.
.. option:: -fsanitize-cfi-icall-generalize-pointers
Generalize pointers in CFI indirect call type signature checks
.. option:: -fsanitize-coverage-allowlist=<arg>, -fsanitize-coverage-whitelist=<arg>
Restrict sanitizer coverage instrumentation exclusively to modules and functions that match the provided special case list, except the blocked ones
.. option:: -fsanitize-coverage-ignorelist=<arg>, -fsanitize-coverage-blacklist=<arg>
Disable sanitizer coverage instrumentation for modules and functions that match the provided special case list, even the allowed ones
.. option:: -fsanitize-coverage=<arg1>,<arg2>..., -fno-sanitize-coverage=<arg1>,<arg2>...
Specify the type of coverage instrumentation for Sanitizers
.. option:: -fsanitize-hwaddress-abi=<arg>
Select the HWAddressSanitizer ABI to target (interceptor or platform, default interceptor). This option is currently unused.
.. option:: -fsanitize-hwaddress-experimental-aliasing, -fno-sanitize-hwaddress-experimental-aliasing
Enable aliasing mode in HWAddressSanitizer
.. option:: -fsanitize-ignorelist=<arg>, -fsanitize-blacklist=<arg>
Path to ignorelist file for sanitizers
.. option:: -fsanitize-link-c++-runtime, -fno-sanitize-link-c++-runtime
.. option:: -fsanitize-link-runtime, -fno-sanitize-link-runtime
.. option:: -fsanitize-memory-track-origins, -fno-sanitize-memory-track-origins
Enable origins tracking in MemorySanitizer
.. program:: clang1
.. option:: -fsanitize-memory-track-origins=<arg>
.. program:: clang
Enable origins tracking in MemorySanitizer
.. option:: -fsanitize-memory-use-after-dtor, -fno-sanitize-memory-use-after-dtor
Enable use-after-destroy detection in MemorySanitizer
.. option:: -fsanitize-minimal-runtime, -fno-sanitize-minimal-runtime
.. option:: -fsanitize-recover=<arg1>,<arg2>..., -fno-sanitize-recover=<arg1>,<arg2>..., -fsanitize-recover (equivalent to -fsanitize-recover=all)
Enable recovery for specified sanitizers
.. option:: -fsanitize-stats, -fno-sanitize-stats
Enable sanitizer statistics gathering.
.. option:: -fsanitize-thread-atomics, -fno-sanitize-thread-atomics
Enable atomic operations instrumentation in ThreadSanitizer (default)
.. option:: -fsanitize-thread-func-entry-exit, -fno-sanitize-thread-func-entry-exit
Enable function entry/exit instrumentation in ThreadSanitizer (default)
.. option:: -fsanitize-thread-memory-access, -fno-sanitize-thread-memory-access
Enable memory access instrumentation in ThreadSanitizer (default)
.. option:: -fsanitize-trap=<arg1>,<arg2>..., -fno-sanitize-trap=<arg1>,<arg2>..., -fsanitize-trap (equivalent to -fsanitize-trap=all), -fsanitize-undefined-trap-on-error (equivalent to -fsanitize-trap=undefined)
Enable trapping for specified sanitizers
.. option:: -fsanitize-undefined-strip-path-components=<number>
Strip (or keep only, if negative) a given number of path components when emitting check metadata.
.. option:: -fsanitize=<check>,<arg2>..., -fno-sanitize=<arg1>,<arg2>...
Turn on runtime checks for various forms of undefined or suspicious behavior. See user manual for available checks
.. option:: -moutline, -mno-outline
Enable function outlining (AArch64 only)
.. option:: -moutline-atomics, -mno-outline-atomics
Generate local calls to out-of-line atomic operations
.. option:: --param <arg>, --param=<arg>
.. option:: -print-supported-cpus, --print-supported-cpus, -mcpu=?, -mtune=?
Print supported cpu models for the given target (if target is not specified, it will print the supported cpus for the default target)
.. option:: -std=<arg>, --std=<arg>, --std <arg>
Language standard to compile for
Preprocessor flags
~~~~~~~~~~~~~~~~~~
Flags controlling the behavior of the Clang preprocessor.
.. option:: -C, --comments
Include comments in preprocessed output
.. option:: -CC, --comments-in-macros
Include comments from within macros in preprocessed output
.. option:: -D<macro>=<value>, --define-macro <arg>, --define-macro=<arg>
Define <macro> to <value> (or 1 if <value> omitted)
.. option:: -H, --trace-includes
Show header includes and nesting depth
.. option:: -P, --no-line-commands
Disable linemarker output in -E mode
.. option:: -U<macro>, --undefine-macro <arg>, --undefine-macro=<arg>
Undefine macro <macro>
.. option:: -Wp,<arg>,<arg2>...
Pass the comma separated arguments in <arg> to the preprocessor
.. option:: -Xpreprocessor <arg>
Pass <arg> to the preprocessor
.. option:: -fmacro-prefix-map=<arg>
remap file source paths in predefined preprocessor macros
Include path management
-----------------------
Flags controlling how ``#include``\s are resolved to files.
.. option:: -I<dir>, --include-directory <arg>, --include-directory=<arg>
Add directory to include search path. For C++ inputs, if
there are multiple -I options, these directories are searched
in the order they are given before the standard system directories
are searched. If the same directory is in the SYSTEM include search
paths, for example if also specified with -isystem, the -I option
will be ignored
.. option:: -I-, --include-barrier
Restrict all prior -I flags to double-quoted inclusion and remove current directory from include path
.. option:: --amdgpu-arch-tool=<arg>
Tool used for detecting AMD GPU arch in the system.
.. option:: --cuda-path-ignore-env
Ignore environment variables to detect CUDA installation
.. option:: --cuda-path=<arg>
CUDA installation path
.. option:: -cxx-isystem<directory>
Add directory to the C++ SYSTEM include search path
.. option:: -fbuild-session-file=<file>
Use the last modification time of <file> as the build session timestamp
.. option:: -fbuild-session-timestamp=<time since Epoch in seconds>
Time when the current build session started
.. option:: -fmodule-file=\[<name>=\]<file>
Specify the mapping of module name to precompiled module file, or load a module file if name is omitted.
.. option:: -fmodules-cache-path=<directory>
Specify the module cache path
.. option:: -fmodules-disable-diagnostic-validation
Disable validation of the diagnostic options when loading the module
.. option:: -fmodules-prune-after=<seconds>
Specify the interval (in seconds) after which a module file will be considered unused
.. option:: -fmodules-prune-interval=<seconds>
Specify the interval (in seconds) between attempts to prune the module cache
.. option:: -fmodules-user-build-path <directory>
Specify the module user build path
.. option:: -fmodules-validate-once-per-build-session
Don't verify input files for the modules if the module has been successfully validated or loaded during this build session
.. option:: -fmodules-validate-system-headers, -fno-modules-validate-system-headers
Validate the system headers that a module depends on when loading the module
.. option:: -fprebuilt-module-path=<directory>
Specify the prebuilt module path
.. option:: --hip-path=<arg>
HIP runtime installation path, used for finding HIP version and adding HIP include path.
.. option:: -idirafter<arg>, --include-directory-after <arg>, --include-directory-after=<arg>
Add directory to AFTER include search path
.. option:: -iframework<arg>
Add directory to SYSTEM framework search path
.. option:: -iframeworkwithsysroot<directory>
Add directory to SYSTEM framework search path, absolute paths are relative to -isysroot
.. option:: -imacros<file>, --imacros<file>, --imacros=<arg>
Include macros from file before parsing
.. option:: -include<file>, --include<file>, --include=<arg>
Include file before parsing
.. option:: -include-pch <file>
Include precompiled header file
.. option:: -iprefix<dir>, --include-prefix <arg>, --include-prefix=<arg>
Set the -iwithprefix/-iwithprefixbefore prefix
.. option:: -iquote<directory>
Add directory to QUOTE include search path
.. option:: -isysroot<dir>
Set the system root directory (usually /)
.. option:: -isystem<directory>
Add directory to SYSTEM include search path
.. option:: -isystem-after<directory>
Add directory to end of the SYSTEM include search path
.. option:: -ivfsoverlay<arg>
Overlay the virtual filesystem described by file over the real file system
.. option:: -iwithprefix<dir>, --include-with-prefix <arg>, --include-with-prefix-after <arg>, --include-with-prefix-after=<arg>, --include-with-prefix=<arg>
Set directory to SYSTEM include search path with prefix
.. option:: -iwithprefixbefore<dir>, --include-with-prefix-before <arg>, --include-with-prefix-before=<arg>
Set directory to include search path with prefix
.. option:: -iwithsysroot<directory>
Add directory to SYSTEM include search path, absolute paths are relative to -isysroot
.. option:: --libomptarget-amdgcn-bc-path=<arg>
Path to libomptarget-amdgcn bitcode library
.. option:: --libomptarget-nvptx-bc-path=<arg>
Path to libomptarget-nvptx bitcode library
.. option:: --ptxas-path=<arg>
Path to ptxas (used for compiling CUDA code)
.. option:: --rocm-path=<arg>
ROCm installation path, used for finding and automatically linking required bitcode libraries.
.. program:: clang1
.. option:: -stdlib++-isystem<directory>
.. program:: clang
Use directory as the C++ standard library include path
.. option:: --system-header-prefix=<prefix>, --no-system-header-prefix=<prefix>, --system-header-prefix <arg>
Treat all #include paths starting with <prefix> as including a system header.
Dependency file generation
--------------------------
Flags controlling generation of a dependency file for ``make``-like build
systems.
.. option:: -M, --dependencies
Like -MD, but also implies -E and writes to stdout by default
.. option:: -MD, --write-dependencies
Write a depfile containing user and system headers
.. option:: -MF<file>
Write depfile output from -MMD, -MD, -MM, or -M to <file>
.. option:: -MG, --print-missing-file-dependencies
Add missing headers to depfile
.. option:: -MJ<arg>
Write a compilation database entry per input
.. option:: -MM, --user-dependencies
Like -MMD, but also implies -E and writes to stdout by default
.. option:: -MMD, --write-user-dependencies
Write a depfile containing user headers
.. option:: -MP
Create phony target for each dependency (other than main file)
.. option:: -MQ<arg>
Specify name of main file output to quote in depfile
.. option:: -MT<arg>
Specify name of main file output in depfile
.. option:: -MV
Use NMake/Jom format for the depfile
Dumping preprocessor state
--------------------------
Flags allowing the state of the preprocessor to be dumped in various ways.
.. option:: -d
.. program:: clang1
.. option:: -d<arg>
.. program:: clang
.. option:: -dD
Print macro definitions in -E mode in addition to normal output
.. option:: -dI
Print include directives in -E mode in addition to normal output
.. option:: -dM
Print macro definitions in -E mode instead of normal output
Diagnostic flags
~~~~~~~~~~~~~~~~
Flags controlling which warnings, errors, and remarks Clang will generate.
See the :doc:`full list of warning and remark flags <DiagnosticsReference>`.
.. option:: -R<remark>
Enable the specified remark
.. option:: -Rpass-analysis=<arg>
Report transformation analysis from optimization passes whose name matches the given POSIX regular expression
.. option:: -Rpass-missed=<arg>
Report missed transformations by optimization passes whose name matches the given POSIX regular expression
.. option:: -Rpass=<arg>
Report transformations performed by optimization passes whose name matches the given POSIX regular expression
.. option:: -W<warning>, --extra-warnings, --warn-<arg>, --warn-=<arg>
Enable the specified warning
.. option:: -Wdeprecated, -Wno-deprecated
Enable warnings for deprecated constructs and define \_\_DEPRECATED
.. option:: -Wnonportable-cfstrings<arg>, -Wno-nonportable-cfstrings<arg>
Target-independent compilation options
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. option:: -Wframe-larger-than=<arg>
.. option:: -fPIC, -fno-PIC
.. option:: -fPIE, -fno-PIE
.. option:: -faccess-control, -fno-access-control
.. option:: -faddrsig, -fno-addrsig
Emit an address-significance table
.. option:: -falign-functions, -fno-align-functions
.. program:: clang1
.. option:: -falign-functions=<arg>
.. program:: clang
.. program:: clang1
.. option:: -faligned-allocation, -faligned-new, -fno-aligned-allocation
.. program:: clang
Enable C++17 aligned allocation functions
.. option:: -fallow-editor-placeholders, -fno-allow-editor-placeholders
Treat editor placeholders as valid source code
.. option:: -fallow-unsupported
.. option:: -faltivec, -fno-altivec
.. option:: -fansi-escape-codes
Use ANSI escape codes for diagnostics
.. option:: -fapple-kext, -findirect-virtual-calls, -fterminated-vtables
Use Apple's kernel extensions ABI
.. option:: -fapple-link-rtlib
Force linking the clang builtins runtime library
.. option:: -fapple-pragma-pack, -fno-apple-pragma-pack
Enable Apple gcc-compatible #pragma pack handling
.. option:: -fapplication-extension, -fno-application-extension
Restrict code to those available for App Extensions
.. option:: -fasm, -fno-asm
.. option:: -fasm-blocks, -fno-asm-blocks
.. option:: -fassociative-math, -fno-associative-math
.. option:: -fassume-sane-operator-new, -fno-assume-sane-operator-new
.. option:: -fast
.. option:: -fastcp
.. option:: -fastf
.. option:: -fasync-exceptions, -fno-async-exceptions
Enable EH Asynchronous exceptions
.. option:: -fasynchronous-unwind-tables, -fno-asynchronous-unwind-tables
.. option:: -fautolink, -fno-autolink
.. option:: -fbasic-block-sections=<arg>
Generate labels for each basic block or place each basic block or a subset of basic blocks in its own section.
.. option:: -fbinutils-version=<major.minor>
Produced object files can use all ELF features supported by this binutils version and newer. If -fno-integrated-as is specified, the generated assembly will consider GNU as support. 'none' means that all ELF features can be used, regardless of binutils support. Defaults to 2.26.
.. option:: -fblocks, -fno-blocks
Enable the 'blocks' language feature
.. option:: -fbootclasspath=<arg>, --bootclasspath <arg>, --bootclasspath=<arg>
.. option:: -fborland-extensions, -fno-borland-extensions
Accept non-standard constructs supported by the Borland compiler
.. option:: -fbracket-depth=<arg>
.. option:: -fbuiltin, -fno-builtin
.. option:: -fbuiltin-module-map
Load the clang builtins module map file.
.. program:: clang1
.. option:: -fc++-static-destructors, -fno-c++-static-destructors
.. program:: clang
.. option:: -fcaret-diagnostics, -fno-caret-diagnostics
.. option:: -fcf-protection=<arg>, -fcf-protection (equivalent to -fcf-protection=full)
Instrument control-flow architecture protection. Options: return, branch, full, none.
.. option:: -fcf-runtime-abi=<arg>
.. option:: -fchar8\_t, -fno-char8\_t
Enable C++ builtin type char8\_t
.. option:: -fclasspath=<arg>, --CLASSPATH <arg>, --CLASSPATH=<arg>, --classpath <arg>, --classpath=<arg>
.. option:: -fcolor-diagnostics, -fno-color-diagnostics
Enable colors in diagnostics
.. option:: -fcommon, -fno-common
Place uninitialized global variables in a common block
.. option:: -fcompile-resource=<arg>, --resource <arg>, --resource=<arg>
.. option:: -fconstant-cfstrings, -fno-constant-cfstrings
.. option:: -fconstant-string-class=<arg>
.. option:: -fconstexpr-backtrace-limit=<arg>
.. option:: -fconstexpr-depth=<arg>
.. option:: -fconstexpr-steps=<arg>
.. option:: -fconvergent-functions
Assume functions may be convergent
.. option:: -fcoroutines-ts, -fno-coroutines-ts
Enable support for the C++ Coroutines TS
.. option:: -fcoverage-compilation-dir=<arg>
The compilation directory to embed in the coverage mapping.
.. option:: -fcoverage-mapping, -fno-coverage-mapping
Generate coverage mapping to enable code coverage analysis
.. option:: -fcoverage-prefix-map=<arg>
remap file source paths in coverage mapping
.. option:: -fcreate-profile
.. option:: -fcs-profile-generate
Generate instrumented code to collect context sensitive execution counts into default.profraw (overridden by LLVM\_PROFILE\_FILE env var)
.. program:: clang1
.. option:: -fcs-profile-generate=<directory>
.. program:: clang
Generate instrumented code to collect context sensitive execution counts into <directory>/default.profraw (overridden by LLVM\_PROFILE\_FILE env var)
.. option:: -fcuda-approx-transcendentals, -fno-cuda-approx-transcendentals
Use approximate transcendental functions
.. option:: -fcuda-short-ptr, -fno-cuda-short-ptr
Use 32-bit pointers for accessing const/local/shared address spaces
.. option:: -fcxx-exceptions, -fno-cxx-exceptions
Enable C++ exceptions
.. option:: -fcxx-modules, -fno-cxx-modules
.. option:: -fdata-sections, -fno-data-sections
Place each data in its own section
.. option:: -fdebug-compilation-dir=<arg>, -fdebug-compilation-dir <arg>
The compilation directory to embed in the debug info
.. option:: -fdebug-default-version=<arg>
Default DWARF version to use, if a -g option caused DWARF debug info to be produced
.. option:: -fdebug-info-for-profiling, -fno-debug-info-for-profiling
Emit extra debug info to make sample profile more accurate
.. option:: -fdebug-macro, -fno-debug-macro
Emit macro debug information
.. option:: -fdebug-pass-arguments
.. option:: -fdebug-pass-structure
.. option:: -fdebug-prefix-map=<arg>
remap file source paths in debug info
.. option:: -fdebug-ranges-base-address, -fno-debug-ranges-base-address
Use DWARF base address selection entries in .debug\_ranges
.. option:: -fdebug-types-section, -fno-debug-types-section
Place debug types in their own section (ELF Only)
.. option:: -fdelayed-template-parsing, -fno-delayed-template-parsing
Parse templated function definitions at the end of the translation unit
.. option:: -fdelete-null-pointer-checks, -fno-delete-null-pointer-checks
Treat usage of null pointers as undefined behavior (default)
.. option:: -fdenormal-fp-math=<arg>
.. option:: -fdiagnostics-absolute-paths
Print absolute paths in diagnostics
.. option:: -fdiagnostics-color, -fno-diagnostics-color
.. program:: clang1
.. option:: -fdiagnostics-color=<arg>
.. program:: clang
.. option:: -fdiagnostics-hotness-threshold=<value>
Prevent optimization remarks from being output if they do not have at least this profile count. Use 'auto' to apply the threshold from profile summary
.. option:: -fdiagnostics-show-hotness, -fno-diagnostics-show-hotness
Enable profile hotness information in diagnostic line
.. option:: -fdiagnostics-show-note-include-stack, -fno-diagnostics-show-note-include-stack
Display include stacks for diagnostic notes
.. option:: -fdiagnostics-show-option, -fno-diagnostics-show-option
Print option name with mappable diagnostics
.. option:: -fdiagnostics-show-template-tree
Print a template comparison tree for differing templates
.. option:: -fdigraphs, -fno-digraphs
Enable alternative token representations '<:', ':>', '<%', '%>', '%:', '%:%:' (default)
.. option:: -fdirect-access-external-data, -fno-direct-access-external-data
Don't use GOT indirection to reference external data symbols
.. option:: -fdollars-in-identifiers, -fno-dollars-in-identifiers
Allow '$' in identifiers
.. option:: -fdouble-square-bracket-attributes, -fno-double-square-bracket-attributes
Enable '\[\[\]\]' attributes in all C and C++ language modes
.. option:: -fdwarf-directory-asm, -fno-dwarf-directory-asm
.. option:: -fdwarf-exceptions
Use DWARF style exceptions
.. option:: -felide-constructors, -fno-elide-constructors
.. option:: -feliminate-unused-debug-symbols, -fno-eliminate-unused-debug-symbols
.. option:: -feliminate-unused-debug-types, -fno-eliminate-unused-debug-types
Do not emit debug info for defined but unused types
.. option:: -fembed-bitcode=<option>, -fembed-bitcode (equivalent to -fembed-bitcode=all), -fembed-bitcode-marker (equivalent to -fembed-bitcode=marker)
Embed LLVM bitcode (option: off, all, bitcode, marker)
.. option:: -femit-all-decls
Emit all declarations, even if unused
.. option:: -femulated-tls, -fno-emulated-tls
Use emutls functions to access thread\_local variables
.. option:: -fenable-matrix
Enable matrix data type and related builtin functions
.. option:: -fencoding=<arg>, --encoding <arg>, --encoding=<arg>
.. option:: -ferror-limit=<arg>
.. option:: -fescaping-block-tail-calls, -fno-escaping-block-tail-calls
.. option:: -fexceptions, -fno-exceptions
Enable support for exception handling
.. option:: -fexec-charset=<arg>
.. option:: -fexperimental-new-constant-interpreter
Enable the experimental new constant interpreter
.. option:: -fextdirs=<arg>, --extdirs <arg>, --extdirs=<arg>
.. option:: -fextend-arguments=<arg>
Controls how scalar integer arguments are extended in calls to unprototyped and varargs functions
.. option:: -ffast-math, -fno-fast-math
Allow aggressive, lossy floating-point optimizations
.. option:: -ffile-compilation-dir=<arg>
The compilation directory to embed in the debug info and coverage mapping.
.. option:: -ffile-prefix-map=<arg>
remap file source paths in debug info and predefined preprocessor macros
.. option:: -ffinite-loops, -fno-finite-loops
Assume all loops are finite.
.. option:: -ffinite-math-only, -fno-finite-math-only
.. option:: -ffixed-point, -fno-fixed-point
Enable fixed point types
.. option:: -ffor-scope, -fno-for-scope
.. option:: -fforce-dwarf-frame, -fno-force-dwarf-frame
Always emit a debug frame section
.. option:: -fforce-emit-vtables, -fno-force-emit-vtables
Emits more virtual tables to improve devirtualization
.. option:: -fforce-enable-int128, -fno-force-enable-int128
Enable support for int128\_t type
.. option:: -ffp-contract=<arg>
Form fused FP ops (e.g. FMAs): fast (fuses across statements disregarding pragmas) \| on (only fuses in the same statement unless dictated by pragmas) \| off (never fuses) \| fast-honor-pragmas (fuses across statements unless diectated by pragmas). Default is 'fast' for CUDA, 'fast-honor-pragmas' for HIP, and 'on' otherwise.
.. option:: -ffp-exception-behavior=<arg>
Specifies the exception behavior of floating-point operations.
.. option:: -ffp-model=<arg>
Controls the semantics of floating-point calculations.
.. option:: -ffreestanding
Assert that the compilation takes place in a freestanding environment
.. option:: -ffunction-sections, -fno-function-sections
Place each function in its own section
.. option:: -fgnu-inline-asm, -fno-gnu-inline-asm
.. option:: -fgnu-keywords, -fno-gnu-keywords
Allow GNU-extension keywords regardless of language standard
.. option:: -fgnu-runtime
Generate output compatible with the standard GNU Objective-C runtime
.. option:: -fgnu89-inline, -fno-gnu89-inline
Use the gnu89 inline semantics
.. option:: -fgnuc-version=<arg>
Sets various macros to claim compatibility with the given GCC version (default is 4.2.1)
.. option:: -fgpu-allow-device-init, -fno-gpu-allow-device-init
Allow device side init function in HIP (experimental)
.. option:: -fgpu-defer-diag, -fno-gpu-defer-diag
Defer host/device related diagnostic messages for CUDA/HIP
.. option:: -fgpu-rdc, -fcuda-rdc, -fno-gpu-rdc
Generate relocatable device code, also known as separate compilation mode
.. option:: -fgpu-sanitize, -fno-gpu-sanitize
Enable sanitizer for AMDGPU target
.. option:: -fhip-fp32-correctly-rounded-divide-sqrt, -fno-hip-fp32-correctly-rounded-divide-sqrt
Specify that single precision floating-point divide and sqrt used in the program source are correctly rounded (HIP device compilation only)
.. option:: -fhip-new-launch-api, -fno-hip-new-launch-api
Use new kernel launching API for HIP
.. option:: -fhonor-infinities, -fhonor-infinites, -fno-honor-infinities
.. option:: -fhonor-nans, -fno-honor-nans
.. option:: -fhosted
.. option:: -fignore-exceptions
Enable support for ignoring exception handling constructs
.. option:: -fimplicit-module-maps, -fmodule-maps, -fno-implicit-module-maps
Implicitly search the file system for module map files.
.. option:: -fimplicit-modules, -fno-implicit-modules
.. option:: -finput-charset=<arg>
Specify the default character set for source files
.. option:: -finstrument-function-entry-bare
Instrument function entry only, after inlining, without arguments to the instrumentation call
.. option:: -finstrument-functions
Generate calls to instrument function entry and exit
.. option:: -finstrument-functions-after-inlining
Like -finstrument-functions, but insert the calls after inlining
.. option:: -fintegrated-as, -fno-integrated-as, -integrated-as
Enable the integrated assembler
.. option:: -fintegrated-cc1, -fno-integrated-cc1
Run cc1 in-process
.. option:: -fjump-tables, -fno-jump-tables
Use jump tables for lowering switches
.. option:: -fkeep-static-consts, -fno-keep-static-consts
Keep static const variables if unused
.. option:: -flax-vector-conversions=<arg>, -flax-vector-conversions (equivalent to -flax-vector-conversions=integer), -fno-lax-vector-conversions (equivalent to -flax-vector-conversions=none)
Enable implicit vector bit-casts
.. option:: -flimited-precision=<arg>
.. option:: -flto, -fno-lto
Enable LTO in 'full' mode
.. option:: -flto-jobs=<arg>
Controls the backend parallelism of -flto=thin (default of 0 means the number of threads will be derived from the number of CPUs detected)
.. program:: clang1
.. option:: -flto=<arg>
.. program:: clang
Set LTO mode to either 'full' or 'thin'
.. program:: clang2
.. option:: -flto=auto
.. program:: clang
.. program:: clang3
.. option:: -flto=jobserver
.. program:: clang
.. option:: -fmacro-backtrace-limit=<arg>
.. option:: -fmath-errno, -fno-math-errno
Require math functions to indicate errors by setting errno
.. option:: -fmax-tokens=<arg>
Max total number of preprocessed tokens for -Wmax-tokens.
.. option:: -fmax-type-align=<arg>
Specify the maximum alignment to enforce on pointers lacking an explicit alignment
.. option:: -fmemory-profile, -fno-memory-profile
Enable heap memory profiling
.. program:: clang1
.. option:: -fmemory-profile=<directory>
.. program:: clang
Enable heap memory profiling and dump results into <directory>
.. option:: -fmerge-all-constants, -fno-merge-all-constants
Allow merging of constants
.. option:: -fmessage-length=<arg>
Format message diagnostics so that they fit within N columns
.. option:: -fmodule-file-deps, -fno-module-file-deps
.. option:: -fmodule-map-file=<file>
Load this module map file
.. option:: -fmodule-name=<name>, -fmodule-implementation-of <arg>
Specify the name of the module to build
.. option:: -fmodules, -fno-modules
Enable the 'modules' language feature
.. option:: -fmodules-decluse, -fno-modules-decluse
Require declaration of modules used within a module
.. option:: -fmodules-ignore-macro=<arg>
Ignore the definition of the given macro when building and loading modules
.. option:: -fmodules-search-all, -fno-modules-search-all
Search even non-imported modules to resolve references
.. option:: -fmodules-strict-decluse
Like -fmodules-decluse but requires all headers to be in modules
.. option:: -fmodules-ts
Enable support for the C++ Modules TS
.. option:: -fmodules-validate-input-files-content
Validate PCM input files based on content if mtime differs
.. option:: -fms-compatibility, -fno-ms-compatibility
Enable full Microsoft Visual C++ compatibility
.. option:: -fms-compatibility-version=<arg>
Dot-separated value representing the Microsoft compiler version number to report in \_MSC\_VER (0 = don't define it (default))
.. option:: -fms-extensions, -fno-ms-extensions
Accept some non-standard constructs supported by the Microsoft compiler
.. option:: -fms-memptr-rep=<arg>
.. option:: -fms-volatile
.. option:: -fmsc-version=<arg>
Microsoft compiler version number to report in \_MSC\_VER (0 = don't define it (default))
.. option:: -fmudflap
.. option:: -fmudflapth
.. option:: -fnested-functions
.. option:: -fnew-alignment=<align>, -fnew-alignment <arg>
Specifies the largest alignment guaranteed by '::operator new(size\_t)'
.. option:: -fnew-infallible
Treats throwing global C++ operator new as always returning valid memory (annotates with \_\_attribute\_\_((returns\_nonnull)) and throw()). This is detectable in source.
.. option:: -fnext-runtime
.. option:: -fno-builtin-<arg>
Disable implicit builtin knowledge of a specific function
.. option:: -fno-elide-type
Do not elide types when printing diagnostics
.. option:: -fno-max-type-align
.. option:: -fno-strict-modules-decluse
.. option:: -fno-temp-file
Directly create compilation output files. This may lead to incorrect incremental builds if the compiler crashes
.. option:: -fno-working-directory
.. option:: -fno\_modules-validate-input-files-content
.. program:: clang1
.. option:: -fno\_pch-validate-input-files-content
.. program:: clang
.. option:: -fnoxray-link-deps
.. option:: -fobjc-abi-version=<arg>
.. option:: -fobjc-arc, -fno-objc-arc
Synthesize retain and release calls for Objective-C pointers
.. option:: -fobjc-arc-exceptions, -fno-objc-arc-exceptions
Use EH-safe code when synthesizing retains and releases in -fobjc-arc
.. option:: -fobjc-convert-messages-to-runtime-calls, -fno-objc-convert-messages-to-runtime-calls
.. option:: -fobjc-disable-direct-methods-for-testing
Ignore attribute objc\_direct so that direct methods can be tested
.. option:: -fobjc-encode-cxx-class-template-spec, -fno-objc-encode-cxx-class-template-spec
Fully encode c++ class template specialization
.. option:: -fobjc-exceptions, -fno-objc-exceptions
Enable Objective-C exceptions
.. option:: -fobjc-infer-related-result-type, -fno-objc-infer-related-result-type
.. option:: -fobjc-legacy-dispatch, -fno-objc-legacy-dispatch
.. option:: -fobjc-link-runtime
.. option:: -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
.. option:: -fobjc-nonfragile-abi-version=<arg>
.. option:: -fobjc-runtime=<arg>
Specify the target Objective-C runtime kind and version
.. option:: -fobjc-sender-dependent-dispatch
.. option:: -fobjc-weak, -fno-objc-weak
Enable ARC-style weak references in Objective-C
.. option:: -foffload-lto, -fno-offload-lto
Enable LTO in 'full' mode for offload compilation
.. program:: clang1
.. option:: -foffload-lto=<arg>
.. program:: clang
Set LTO mode to either 'full' or 'thin' for offload compilation
.. option:: -fomit-frame-pointer, -fno-omit-frame-pointer
.. option:: -fopenmp, -fno-openmp
Parse OpenMP pragmas and generate parallel code.
.. option:: -fopenmp-simd, -fno-openmp-simd
Emit OpenMP code only for SIMD-based constructs.
.. option:: -fopenmp-version=<arg>
.. program:: clang1
.. option:: -fopenmp=<arg>
.. program:: clang
.. option:: -foperator-arrow-depth=<arg>
.. option:: -foperator-names, -fno-operator-names
.. option:: -foptimization-record-file=<file>
Specify the output name of the file containing the optimization remarks. Implies -fsave-optimization-record. On Darwin platforms, this cannot be used with multiple -arch <arch> options.
.. option:: -foptimization-record-passes=<regex>
Only include passes which match a specified regular expression in the generated optimization record (by default, include all passes)
.. option:: -foptimize-sibling-calls, -fno-optimize-sibling-calls
.. option:: -forder-file-instrumentation
Generate instrumented code to collect order file into default.profraw file (overridden by '=' form of option or LLVM\_PROFILE\_FILE env var)
.. option:: -foutput-class-dir=<arg>, --output-class-directory <arg>, --output-class-directory=<arg>
.. option:: -fpack-struct, -fno-pack-struct
.. program:: clang1
.. option:: -fpack-struct=<arg>
.. program:: clang
Specify the default maximum struct packing alignment
.. option:: -fpascal-strings, -fno-pascal-strings, -mpascal-strings
Recognize and construct Pascal-style string literals
.. option:: -fpass-plugin=<dsopath>
Load pass plugin from a dynamic shared object file (only with new pass manager).
.. option:: -fpatchable-function-entry=<N,M>
Generate M NOPs before function entry and N-M NOPs after function entry
.. option:: -fpcc-struct-return
Override the default ABI to return all structs on the stack
.. option:: -fpch-codegen, -fno-pch-codegen
Generate code for uses of this PCH that assumes an explicit object file will be built for the PCH
.. option:: -fpch-debuginfo, -fno-pch-debuginfo
Generate debug info for types in an object file built from this PCH and do not generate them elsewhere
.. option:: -fpch-instantiate-templates, -fno-pch-instantiate-templates
Instantiate templates already while building a PCH
.. option:: -fpch-preprocess
.. option:: -fpch-validate-input-files-content
Validate PCH input files based on content if mtime differs
.. option:: -fpic, -fno-pic
.. option:: -fpie, -fno-pie
.. option:: -fplt, -fno-plt
.. option:: -fplugin=<dsopath>
Load the named plugin (dynamic shared object)
.. option:: -fprebuilt-implicit-modules, -fno-prebuilt-implicit-modules
Look up implicit modules in the prebuilt module path
.. option:: -fpreserve-as-comments, -fno-preserve-as-comments
.. option:: -fproc-stat-report<arg>
Print subprocess statistics
.. program:: clang1
.. option:: -fproc-stat-report=<arg>
.. program:: clang
Save subprocess statistics to the given file
.. option:: -fprofile-arcs, -fno-profile-arcs
.. option:: -fprofile-dir=<arg>
.. option:: -fprofile-exclude-files=<arg>
Instrument only functions from files where names don't match all the regexes separated by a semi-colon
.. option:: -fprofile-filter-files=<arg>
Instrument only functions from files where names match any regex separated by a semi-colon
.. option:: -fprofile-generate, -fno-profile-generate
Generate instrumented code to collect execution counts into default.profraw (overridden by LLVM\_PROFILE\_FILE env var)
.. program:: clang1
.. option:: -fprofile-generate=<directory>
.. program:: clang
Generate instrumented code to collect execution counts into <directory>/default.profraw (overridden by LLVM\_PROFILE\_FILE env var)
.. option:: -fprofile-instr-generate, -fno-profile-instr-generate
Generate instrumented code to collect execution counts into default.profraw file (overridden by '=' form of option or LLVM\_PROFILE\_FILE env var)
.. program:: clang1
.. option:: -fprofile-instr-generate=<file>
.. program:: clang
Generate instrumented code to collect execution counts into <file> (overridden by LLVM\_PROFILE\_FILE env var)
.. option:: -fprofile-instr-use, -fno-profile-instr-use, -fprofile-use
.. program:: clang1
.. option:: -fprofile-instr-use=<arg>
.. program:: clang
Use instrumentation data for profile-guided optimization
.. option:: -fprofile-list=<arg>
Filename defining the list of functions/files to instrument
.. option:: -fprofile-remapping-file=<file>
Use the remappings described in <file> to match the profile data against names in the program
.. option:: -fprofile-sample-accurate, -fauto-profile-accurate, -fno-profile-sample-accurate
Specifies that the sample profile is accurate. If the sample
profile is accurate, callsites without profile samples are marked
as cold. Otherwise, treat callsites without profile samples as if
we have no profile
.. option:: -fprofile-sample-use, -fauto-profile, -fno-profile-sample-use
.. program:: clang1
.. option:: -fprofile-sample-use=<arg>, -fauto-profile=<arg>
.. program:: clang
Enable sample-based profile guided optimizations
.. option:: -fprofile-update=<method>
Set update method of profile counters (atomic,prefer-atomic,single)
.. program:: clang1
.. option:: -fprofile-use=<pathname>
.. program:: clang
Use instrumentation data for profile-guided optimization. If pathname is a directory, it reads from <pathname>/default.profdata. Otherwise, it reads from file <pathname>.
.. option:: -fpseudo-probe-for-profiling, -fno-pseudo-probe-for-profiling
Emit pseudo probes for sample profiling
.. option:: -freciprocal-math, -fno-reciprocal-math
Allow division operations to be reassociated
.. option:: -freg-struct-return
Override the default ABI to return small structs in registers
.. option:: -fregister-global-dtors-with-atexit, -fno-register-global-dtors-with-atexit
Use atexit or \_\_cxa\_atexit to register global destructors
.. option:: -frelaxed-template-template-args, -fno-relaxed-template-template-args
Enable C++17 relaxed template template argument matching
.. option:: -freroll-loops, -fno-reroll-loops
Turn on loop reroller
.. option:: -fretain-comments-from-system-headers
.. option:: -frewrite-imports, -fno-rewrite-imports
.. option:: -frewrite-includes, -fno-rewrite-includes
.. option:: -frewrite-map-file=<arg>
.. option:: -fropi, -fno-ropi
Generate read-only position independent code (ARM only)
.. option:: -frounding-math, -fno-rounding-math
.. option:: -frtti, -fno-rtti
.. option:: -frtti-data, -fno-rtti-data
.. option:: -frwpi, -fno-rwpi
Generate read-write position independent code (ARM only)
.. option:: -fsave-optimization-record, -fno-save-optimization-record
Generate a YAML optimization record file
.. program:: clang1
.. option:: -fsave-optimization-record=<format>
.. program:: clang
Generate an optimization record file in a specific format
.. option:: -fseh-exceptions
Use SEH style exceptions
.. option:: -fsemantic-interposition, -fno-semantic-interposition
.. option:: -fshort-enums, -fno-short-enums
Allocate to an enum type only as many bytes as it needs for the declared range of possible values
.. option:: -fshort-wchar, -fno-short-wchar
Force wchar\_t to be a short unsigned int
.. option:: -fshow-column, -fno-show-column
.. option:: -fshow-overloads=<arg>
Which overload candidates to show when overload resolution fails: best\|all; defaults to all
.. option:: -fshow-source-location, -fno-show-source-location
.. option:: -fsignaling-math, -fno-signaling-math
.. option:: -fsigned-bitfields
.. option:: -fsigned-char, -fno-signed-char, --signed-char
char is signed
.. option:: -fsigned-zeros, -fno-signed-zeros
.. option:: -fsized-deallocation, -fno-sized-deallocation
Enable C++14 sized global deallocation functions
.. option:: -fsjlj-exceptions
Use SjLj style exceptions
.. option:: -fslp-vectorize, -fno-slp-vectorize, -ftree-slp-vectorize
Enable the superword-level parallelism vectorization passes
.. option:: -fspell-checking, -fno-spell-checking
.. option:: -fspell-checking-limit=<arg>
.. option:: -fsplit-dwarf-inlining, -fno-split-dwarf-inlining
Provide minimal debug info in the object/executable to facilitate online symbolication/stack traces in the absence of .dwo/.dwp files when using Split DWARF
.. option:: -fsplit-lto-unit, -fno-split-lto-unit
Enables splitting of the LTO unit
.. option:: -fsplit-machine-functions, -fno-split-machine-functions
Enable late function splitting using profile information (x86 ELF)
.. option:: -fsplit-stack, -fno-split-stack
Use segmented stack
.. option:: -fstack-clash-protection, -fno-stack-clash-protection
Enable stack clash protection
.. option:: -fstack-protector, -fno-stack-protector
Enable stack protectors for some functions vulnerable to stack smashing. This uses a loose heuristic which considers functions vulnerable if they contain a char (or 8bit integer) array or constant sized calls to alloca , which are of greater size than ssp-buffer-size (default: 8 bytes). All variable sized calls to alloca are considered vulnerable. A function with a stack protector has a guard value added to the stack frame that is checked on function exit. The guard value must be positioned in the stack frame such that a buffer overflow from a vulnerable variable will overwrite the guard value before overwriting the function's return address. The reference stack guard value is stored in a global variable.
.. option:: -fstack-protector-all
Enable stack protectors for all functions
.. option:: -fstack-protector-strong
Enable stack protectors for some functions vulnerable to stack smashing. Compared to -fstack-protector, this uses a stronger heuristic that includes functions containing arrays of any size (and any type), as well as any calls to alloca or the taking of an address from a local variable
.. option:: -fstack-size-section, -fno-stack-size-section
Emit section containing metadata on function stack sizes
.. option:: -fstack-usage
Emit .su file containing information on function stack sizes
.. option:: -fstandalone-debug, -fno-limit-debug-info, -fno-standalone-debug
Emit full debug info for all types used by the program
.. option:: -fstrict-aliasing, -fno-strict-aliasing
.. option:: -fstrict-enums, -fno-strict-enums
Enable optimizations based on the strict definition of an enum's value range
.. option:: -fstrict-float-cast-overflow, -fno-strict-float-cast-overflow
Assume that overflowing float-to-int casts are undefined (default)
.. option:: -fstrict-overflow, -fno-strict-overflow
.. option:: -fstrict-return, -fno-strict-return
.. option:: -fstrict-vtable-pointers, -fno-strict-vtable-pointers
Enable optimizations based on the strict rules for overwriting polymorphic C++ objects
.. option:: -fstruct-path-tbaa, -fno-struct-path-tbaa
.. option:: -fsymbol-partition=<arg>
.. option:: -ftabstop=<arg>
.. option:: -ftemplate-backtrace-limit=<arg>
.. option:: -ftemplate-depth-<arg>
.. option:: -ftemplate-depth=<arg>
.. option:: -ftest-coverage, -fno-test-coverage
.. option:: -fthin-link-bitcode=<arg>
Write minimized bitcode to <file> for the ThinLTO thin link only
.. option:: -fthinlto-index=<arg>
Perform ThinLTO importing using provided function summary index
.. option:: -fthreadsafe-statics, -fno-threadsafe-statics
.. option:: -ftime-report
.. program:: clang1
.. option:: -ftime-report=<arg>
.. program:: clang
(For new pass manager) "per-pass": one report for each pass; "per-pass-run": one report for each pass invocation
.. option:: -ftime-trace
Turn on time profiler. Generates JSON file based on output filename. Results
can be analyzed with chrome://tracing or `Speedscope App
<https://www.speedscope.app>`_ for flamegraph visualization.
.. option:: -ftime-trace-granularity=<arg>
Minimum time granularity (in microseconds) traced by time profiler
.. option:: -ftls-model=<arg>
.. option:: -ftrap-function=<arg>
Issue call to specified function rather than a trap instruction
.. option:: -ftrapping-math, -fno-trapping-math
.. option:: -ftrapv
Trap on integer overflow
.. option:: -ftrapv-handler <arg>
.. program:: clang1
.. option:: -ftrapv-handler=<function name>
.. program:: clang
Specify the function to be called on overflow
.. option:: -ftrigraphs, -fno-trigraphs, -trigraphs, --trigraphs
Process trigraph sequences
.. option:: -ftrivial-auto-var-init-stop-after=<arg>
Stop initializing trivial automatic stack variables after the specified number of instances
.. option:: -ftrivial-auto-var-init=<arg>
Initialize trivial automatic stack variables: uninitialized (default) \| pattern
.. option:: -funique-basic-block-section-names, -fno-unique-basic-block-section-names
Use unique names for basic block sections (ELF Only)
.. option:: -funique-internal-linkage-names, -fno-unique-internal-linkage-names
Uniqueify Internal Linkage Symbol Names by appending the MD5 hash of the module path
.. option:: -funique-section-names, -fno-unique-section-names
.. option:: -funit-at-a-time, -fno-unit-at-a-time
.. option:: -funroll-loops, -fno-unroll-loops
Turn on loop unroller
.. option:: -funsafe-math-optimizations, -fno-unsafe-math-optimizations
.. option:: -funsigned-bitfields
.. option:: -funsigned-char, -fno-unsigned-char, --unsigned-char
.. option:: -funwind-tables, -fno-unwind-tables
.. option:: -fuse-cxa-atexit, -fno-use-cxa-atexit
.. option:: -fuse-init-array, -fno-use-init-array
.. option:: -fuse-ld=<arg>
.. option:: -fuse-line-directives, -fno-use-line-directives
Use #line in preprocessed output
.. option:: -fminimize-whitespace, -fno-minimize-whitespace
Ignore the whitespace from the input file when emitting preprocessor
output. It will only contain whitespace when necessary, e.g. to keep two
minus signs from merging into to an increment operator. Useful with the
-P option to normalize whitespace such that two files with only formatting
changes are equal.
Only valid with -E on C-like inputs and incompatible with -traditional-cpp.
.. option:: -fvalidate-ast-input-files-content
Compute and store the hash of input files used to build an AST. Files with mismatching mtime's are considered valid if both contents is identical
.. option:: -fveclib=<arg>
Use the given vector functions library
.. option:: -fvectorize, -fno-vectorize, -ftree-vectorize
Enable the loop vectorization passes
.. option:: -fverbose-asm, -dA, -fno-verbose-asm
Generate verbose assembly output
.. option:: -fvirtual-function-elimination, -fno-virtual-function-elimination
Enables dead virtual function elimination optimization. Requires -flto=full
.. option:: -fvisibility-dllexport=<arg>
The visibility for dllexport definitions \[-fvisibility-from-dllstorageclass\]
.. option:: -fvisibility-externs-dllimport=<arg>
The visibility for dllimport external declarations \[-fvisibility-from-dllstorageclass\]
.. option:: -fvisibility-externs-nodllstorageclass=<arg>
The visibility for external declarations without an explicit DLL dllstorageclass \[-fvisibility-from-dllstorageclass\]
.. option:: -fvisibility-from-dllstorageclass, -fno-visibility-from-dllstorageclass
Set the visibility of symbols in the generated code from their DLL storage class
.. option:: -fvisibility-global-new-delete-hidden
Give global C++ operator new and delete declarations hidden visibility
.. option:: -fvisibility-inlines-hidden, -fno-visibility-inlines-hidden
Give inline C++ member functions hidden visibility by default
.. option:: -fvisibility-inlines-hidden-static-local-var, -fno-visibility-inlines-hidden-static-local-var
When -fvisibility-inlines-hidden is enabled, static variables in inline C++ member functions will also be given hidden visibility by default
.. option:: -fvisibility-ms-compat
Give global types 'default' visibility and global functions and variables 'hidden' visibility by default
.. option:: -fvisibility-nodllstorageclass=<arg>
The visibility for defintiions without an explicit DLL export class \[-fvisibility-from-dllstorageclass\]
.. option:: -fvisibility=<arg>
Set the default symbol visibility for all global declarations
.. option:: -fwarn-stack-size=<arg>
.. option:: -fwasm-exceptions
Use WebAssembly style exceptions
.. option:: -fwhole-program-vtables, -fno-whole-program-vtables
Enables whole-program vtable optimization. Requires -flto
.. option:: -fwrapv, -fno-wrapv
Treat signed integer overflow as two's complement
.. option:: -fwritable-strings
Store string literals as writable data
.. option:: -fxl-pragma-pack, -fno-xl-pragma-pack
Enable IBM XL #pragma pack handling
.. option:: -fxray-always-emit-customevents, -fno-xray-always-emit-customevents
Always emit \_\_xray\_customevent(...) calls even if the containing function is not always instrumented
.. option:: -fxray-always-emit-typedevents, -fno-xray-always-emit-typedevents
Always emit \_\_xray\_typedevent(...) calls even if the containing function is not always instrumented
.. option:: -fxray-always-instrument=<arg>
DEPRECATED: Filename defining the whitelist for imbuing the 'always instrument' XRay attribute.
.. option:: -fxray-attr-list=<arg>
Filename defining the list of functions/types for imbuing XRay attributes.
.. option:: -fxray-function-groups=<arg>
Only instrument 1 of N groups
.. option:: -fxray-function-index, -fno-xray-function-index
.. option:: -fxray-ignore-loops, -fno-xray-ignore-loops
Don't instrument functions with loops unless they also meet the minimum function size
.. option:: -fxray-instruction-threshold<arg>
.. program:: clang1
.. option:: -fxray-instruction-threshold=<arg>
.. program:: clang
Sets the minimum function size to instrument with XRay
.. option:: -fxray-instrument, -fno-xray-instrument
Generate XRay instrumentation sleds on function entry and exit
.. option:: -fxray-instrumentation-bundle=<arg>
Select which XRay instrumentation points to emit. Options: all, none, function-entry, function-exit, function, custom. Default is 'all'. 'function' includes both 'function-entry' and 'function-exit'.
.. option:: -fxray-link-deps
Tells clang to add the link dependencies for XRay.
.. option:: -fxray-modes=<arg>
List of modes to link in by default into XRay instrumented binaries.
.. option:: -fxray-never-instrument=<arg>
DEPRECATED: Filename defining the whitelist for imbuing the 'never instrument' XRay attribute.
.. option:: -fxray-selected-function-group=<arg>
When using -fxray-function-groups, select which group of functions to instrument. Valid range is 0 to fxray-function-groups - 1
.. option:: -fzero-initialized-in-bss, -fno-zero-initialized-in-bss
.. option:: -fzvector, -fno-zvector, -mzvector
Enable System z vector language extension
.. option:: --gpu-bundle-output, --no-gpu-bundle-output
Bundle output files of HIP device compilation
.. option:: -pedantic, --pedantic, -no-pedantic, --no-pedantic
Warn on language extensions
.. option:: -pedantic-errors, --pedantic-errors
OpenCL flags
------------
.. option:: -cl-denorms-are-zero
OpenCL only. Allow denormals to be flushed to zero.
.. option:: -cl-fast-relaxed-math
OpenCL only. Sets -cl-finite-math-only and -cl-unsafe-math-optimizations, and defines \_\_FAST\_RELAXED\_MATH\_\_.
.. option:: -cl-finite-math-only
OpenCL only. Allow floating-point optimizations that assume arguments and results are not NaNs or +-Inf.
.. option:: -cl-fp32-correctly-rounded-divide-sqrt
OpenCL only. Specify that single precision floating-point divide and sqrt used in the program source are correctly rounded.
.. option:: -cl-kernel-arg-info
OpenCL only. Generate kernel argument metadata.
.. option:: -cl-mad-enable
OpenCL only. Allow use of less precise MAD computations in the generated binary.
.. option:: -cl-no-signed-zeros
OpenCL only. Allow use of less precise no signed zeros computations in the generated binary.
.. option:: -cl-no-stdinc
OpenCL only. Disables all standard includes containing non-native compiler types and functions.
.. option:: -cl-opt-disable
OpenCL only. This option disables all optimizations. By default optimizations are enabled.
.. option:: -cl-single-precision-constant
OpenCL only. Treat double precision floating-point constant as single precision constant.
.. option:: -cl-std=<arg>
OpenCL language standard to compile for.
.. option:: -cl-strict-aliasing
OpenCL only. This option is added for compatibility with OpenCL 1.0.
.. option:: -cl-uniform-work-group-size
OpenCL only. Defines that the global work-size be a multiple of the work-group size specified to clEnqueueNDRangeKernel
.. option:: -cl-unsafe-math-optimizations
OpenCL only. Allow unsafe floating-point optimizations. Also implies -cl-no-signed-zeros and -cl-mad-enable.
SYCL flags
----------
.. option:: -fsycl, -fno-sycl
Enables SYCL kernels compilation for device
.. option:: -sycl-std=<arg>
SYCL language standard to compile for.
Target-dependent compilation options
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. option:: -G<size>, -G=<arg>, -msmall-data-limit=<arg>, -msmall-data-threshold=<arg>
Put objects of at most <size> bytes into small data section (MIPS / Hexagon)
.. option:: -ffixed-x1
Reserve the x1 register (AArch64/RISC-V only)
.. option:: -ffixed-x10
Reserve the x10 register (AArch64/RISC-V only)
.. option:: -ffixed-x11
Reserve the x11 register (AArch64/RISC-V only)
.. option:: -ffixed-x12
Reserve the x12 register (AArch64/RISC-V only)
.. option:: -ffixed-x13
Reserve the x13 register (AArch64/RISC-V only)
.. option:: -ffixed-x14
Reserve the x14 register (AArch64/RISC-V only)
.. option:: -ffixed-x15
Reserve the x15 register (AArch64/RISC-V only)
.. option:: -ffixed-x16
Reserve the x16 register (AArch64/RISC-V only)
.. option:: -ffixed-x17
Reserve the x17 register (AArch64/RISC-V only)
.. option:: -ffixed-x18
Reserve the x18 register (AArch64/RISC-V only)
.. option:: -ffixed-x19
Reserve the x19 register (AArch64/RISC-V only)
.. option:: -ffixed-x2
Reserve the x2 register (AArch64/RISC-V only)
.. option:: -ffixed-x20
Reserve the x20 register (AArch64/RISC-V only)
.. option:: -ffixed-x21
Reserve the x21 register (AArch64/RISC-V only)
.. option:: -ffixed-x22
Reserve the x22 register (AArch64/RISC-V only)
.. option:: -ffixed-x23
Reserve the x23 register (AArch64/RISC-V only)
.. option:: -ffixed-x24
Reserve the x24 register (AArch64/RISC-V only)
.. option:: -ffixed-x25
Reserve the x25 register (AArch64/RISC-V only)
.. option:: -ffixed-x26
Reserve the x26 register (AArch64/RISC-V only)
.. option:: -ffixed-x27
Reserve the x27 register (AArch64/RISC-V only)
.. option:: -ffixed-x28
Reserve the x28 register (AArch64/RISC-V only)
.. option:: -ffixed-x29
Reserve the x29 register (AArch64/RISC-V only)
.. option:: -ffixed-x3
Reserve the x3 register (AArch64/RISC-V only)
.. option:: -ffixed-x30
Reserve the x30 register (AArch64/RISC-V only)
.. option:: -ffixed-x31
Reserve the x31 register (AArch64/RISC-V only)
.. option:: -ffixed-x4
Reserve the x4 register (AArch64/RISC-V only)
.. option:: -ffixed-x5
Reserve the x5 register (AArch64/RISC-V only)
.. option:: -ffixed-x6
Reserve the x6 register (AArch64/RISC-V only)
.. option:: -ffixed-x7
Reserve the x7 register (AArch64/RISC-V only)
.. option:: -ffixed-x8
Reserve the x8 register (AArch64/RISC-V only)
.. option:: -ffixed-x9
Reserve the x9 register (AArch64/RISC-V only)
.. option:: -m16
.. option:: -m32
.. option:: -m64
.. option:: -mabi=<arg>
.. program:: clang1
.. option:: -mabi=vec-default
.. program:: clang
Enable the default Altivec ABI on AIX (AIX only). Uses only volatile vector registers.
.. program:: clang2
.. option:: -mabi=vec-extabi
.. program:: clang
Enable the extended Altivec ABI on AIX (AIX only). Uses volatile and nonvolatile vector registers
.. option:: -maix-struct-return
Return all structs in memory (PPC32 only)
.. option:: -malign-branch-boundary=<arg>
Specify the boundary's size to align branches
.. option:: -malign-branch=<arg1>,<arg2>...
Specify types of branches to align
.. option:: -malign-double
Align doubles to two words in structs (x86 only)
.. option:: -mamdgpu-ieee, -mno-amdgpu-ieee
Sets the IEEE bit in the expected default floating point mode register. Floating point opcodes that support exception flag gathering quiet and propagate signaling NaN inputs per IEEE 754-2008. This option changes the ABI. (AMDGPU only)
.. option:: -march=<arg>
.. option:: -masm=<arg>
.. option:: -mbackchain, -mno-backchain
Link stack frames through backchain on System Z
.. option:: -mbranches-within-32B-boundaries
Align selected branches (fused, jcc, jmp) within 32-byte boundary
.. option:: -mcmodel=<arg>, -mcmodel=medany (equivalent to -mcmodel=medium), -mcmodel=medlow (equivalent to -mcmodel=small)
.. option:: -mcode-object-v3, -mno-code-object-v3
Legacy option to specify code object ABI V3 (AMDGPU only)
.. option:: -mcode-object-version=<version>
Specify code object ABI version. Defaults to 3. (AMDGPU only)
.. option:: -mconsole<arg>
.. program:: clang1
.. option:: -mcpu=<arg>, -mv5 (equivalent to -mcpu=hexagonv5), -mv55 (equivalent to -mcpu=hexagonv55), -mv60 (equivalent to -mcpu=hexagonv60), -mv62 (equivalent to -mcpu=hexagonv62), -mv65 (equivalent to -mcpu=hexagonv65), -mv66 (equivalent to -mcpu=hexagonv66), -mv67 (equivalent to -mcpu=hexagonv67), -mv67t (equivalent to -mcpu=hexagonv67t), -mv68 (equivalent to -mcpu=hexagonv68)
.. program:: clang
.. option:: -mcrc, -mno-crc
Allow use of CRC instructions (ARM/Mips only)
.. option:: -mdefault-build-attributes<arg>, -mno-default-build-attributes<arg>
.. option:: -mdll<arg>
.. option:: -mdouble=<arg>
Force double to be 32 bits or 64 bits
.. option:: -mdynamic-no-pic<arg>
.. option:: -meabi <arg>
Set EABI type, e.g. 4, 5 or gnu (default depends on triple)
.. option:: -menable-experimental-extensions
Enable use of experimental RISC-V extensions.
.. option:: -mfentry
Insert calls to fentry at function entry (x86/SystemZ only)
.. option:: -mfloat-abi=<arg>
.. option:: -mfpmath=<arg>
.. option:: -mfpu=<arg>
.. option:: -mglobal-merge, -mno-global-merge
Enable merging of globals
.. option:: -mhard-float
.. option:: -mhwdiv=<arg>, --mhwdiv <arg>, --mhwdiv=<arg>
.. option:: -mhwmult=<arg>
.. option:: -miamcu, -mno-iamcu
Use Intel MCU ABI
.. option:: -mignore-xcoff-visibility
Not emit the visibility attribute for asm in AIX OS or give all symbols 'unspecified' visibility in XCOFF object file
.. option:: -mimplicit-float, -mno-implicit-float
.. option:: -mimplicit-it=<arg>
.. option:: -mincremental-linker-compatible, -mno-incremental-linker-compatible
(integrated-as) Emit an object file which can be used with an incremental linker
.. option:: -miphoneos-version-min=<arg>, -mios-version-min=<arg>
.. option:: -mkernel
.. option:: -mlong-calls, -mno-long-calls
Generate branches with extended addressability, usually via indirect jumps.
.. option:: -mlvi-cfi, -mno-lvi-cfi
Enable only control-flow mitigations for Load Value Injection (LVI)
.. option:: -mlvi-hardening, -mno-lvi-hardening
Enable all mitigations for Load Value Injection (LVI)
.. option:: -mmacosx-version-min=<arg>, -mmacos-version-min=<arg>
Set Mac OS X deployment target
.. option:: -mmcu=<arg>
.. option:: -mms-bitfields, -mno-ms-bitfields
Set the default structure layout to be compatible with the Microsoft compiler standard
.. option:: -mnop-mcount
Generate mcount/\_\_fentry\_\_ calls as nops. To activate they need to be patched in.
.. option:: -momit-leaf-frame-pointer, -mno-omit-leaf-frame-pointer
Omit frame pointer setup for leaf functions
.. option:: -moslib=<arg>
.. option:: -mpacked-stack, -mno-packed-stack
Use packed stack layout (SystemZ only).
.. option:: -mpad-max-prefix-size=<arg>
Specify maximum number of prefixes to use for padding
.. option:: -mprefer-vector-width=<arg>
Specifies preferred vector width for auto-vectorization. Defaults to 'none' which allows target specific decisions.
.. option:: -mqdsp6-compat
Enable hexagon-qdsp6 backward compatibility
.. option:: -mrecip
.. program:: clang1
.. option:: -mrecip=<arg1>,<arg2>...
.. program:: clang
.. option:: -mrecord-mcount
Generate a \_\_mcount\_loc section entry for each \_\_fentry\_\_ call.
.. option:: -mred-zone, -mno-red-zone
.. option:: -mregparm=<arg>
.. option:: -mrelax, -mno-relax
Enable linker relaxation
.. option:: -mrelax-all, -mno-relax-all
(integrated-as) Relax all machine instructions
.. option:: -mretpoline, -mno-retpoline
.. option:: -mrtd, -mno-rtd
Make StdCall calling convention the default
.. option:: -mseses, -mno-seses
Enable speculative execution side effect suppression (SESES). Includes LVI control flow integrity mitigations
.. option:: -msign-return-address=<arg>
Select return address signing scope
.. option:: -msim
.. option:: -msoft-float, -mno-soft-float
Use software floating point
.. option:: -mspeculative-load-hardening, -mno-speculative-load-hardening
.. option:: -mstack-alignment=<arg>
Set the stack alignment
.. option:: -mstack-arg-probe, -mno-stack-arg-probe
Enable stack probes
.. option:: -mstack-probe-size=<arg>
Set the stack probe size
.. option:: -mstack-protector-guard-offset=<arg>
Use the given offset for addressing the stack-protector guard
.. option:: -mstack-protector-guard-reg=<arg>
Use the given reg for addressing the stack-protector guard
.. option:: -mstack-protector-guard=<arg>
Use the given guard (global, tls) for addressing the stack-protector guard
.. option:: -mstackrealign, -mno-stackrealign
Force realign the stack at entry to every function
.. option:: -msvr4-struct-return
Return small structs in registers (PPC32 only)
.. option:: -mthread-model <arg>
The thread model to use, e.g. posix, single (posix by default)
.. option:: -mthreads<arg>
.. option:: -mthumb, -mno-thumb
.. option:: -mtls-direct-seg-refs, -mno-tls-direct-seg-refs
Enable direct TLS access through segment registers (default)
.. option:: -mtls-size=<arg>
Specify bit size of immediate TLS offsets (AArch64 ELF only): 12 (for 4KB) \| 24 (for 16MB, default) \| 32 (for 4GB) \| 48 (for 256TB, needs -mcmodel=large)
.. program:: clang1
.. option:: -mtune=<arg>
.. program:: clang
Only supported on X86 and RISC-V. Otherwise accepted for compatibility with GCC.
.. option:: -mtvos-version-min=<arg>, -mappletvos-version-min=<arg>
.. option:: -municode<arg>
.. option:: -munsafe-fp-atomics, -mno-unsafe-fp-atomics
Enable unsafe floating point atomic instructions (AMDGPU only)
.. option:: -mvx, -mno-vx
.. option:: -mwarn-nonportable-cfstrings, -mno-warn-nonportable-cfstrings
.. option:: -mwatchos-version-min=<arg>
.. option:: -mwavefrontsize64, -mno-wavefrontsize64
Specify wavefront size 64 mode (AMDGPU only)
.. option:: -mwindows<arg>
.. option:: -mx32
AARCH64
-------
.. option:: -fcall-saved-x10
Make the x10 register call-saved (AArch64 only)
.. option:: -fcall-saved-x11
Make the x11 register call-saved (AArch64 only)
.. option:: -fcall-saved-x12
Make the x12 register call-saved (AArch64 only)
.. option:: -fcall-saved-x13
Make the x13 register call-saved (AArch64 only)
.. option:: -fcall-saved-x14
Make the x14 register call-saved (AArch64 only)
.. option:: -fcall-saved-x15
Make the x15 register call-saved (AArch64 only)
.. option:: -fcall-saved-x18
Make the x18 register call-saved (AArch64 only)
.. option:: -fcall-saved-x8
Make the x8 register call-saved (AArch64 only)
.. option:: -fcall-saved-x9
Make the x9 register call-saved (AArch64 only)
.. option:: -mfix-cortex-a53-835769, -mno-fix-cortex-a53-835769
Workaround Cortex-A53 erratum 835769 (AArch64 only)
.. option:: -mgeneral-regs-only
Generate code which only uses the general purpose registers (AArch64 only)
.. option:: -mmark-bti-property
Add .note.gnu.property with BTI to assembly files (AArch64 only)
.. option:: -msve-vector-bits=<arg>
Specify the size in bits of an SVE vector register. Defaults to the vector length agnostic value of "scalable". (AArch64 only)
AMDGPU
------
.. option:: -mcumode, -mno-cumode
Specify CU wavefront execution mode (AMDGPU only)
.. option:: -mtgsplit, -mno-tgsplit
Enable threadgroup split execution mode (AMDGPU only)
ARM
---
.. option:: -faapcs-bitfield-load
Follows the AAPCS standard that all volatile bit-field write generates at least one load. (ARM only).
.. option:: -faapcs-bitfield-width, -fno-aapcs-bitfield-width
Follow the AAPCS standard requirement stating that volatile bit-field width is dictated by the field container type. (ARM only).
.. option:: -ffixed-r9
Reserve the r9 register (ARM only)
.. option:: -mcmse
Allow use of CMSE (Armv8-M Security Extensions)
.. option:: -mexecute-only, -mno-execute-only, -mpure-code
Disallow generation of data access to code sections (ARM only)
.. option:: -mno-movt
Disallow use of movt/movw pairs (ARM only)
.. option:: -mno-neg-immediates
Disallow converting instructions with negative immediates to their negation or inversion.
.. option:: -mnocrc
Disallow use of CRC instructions (ARM only)
.. option:: -mrestrict-it, -mno-restrict-it
Disallow generation of deprecated IT blocks for ARMv8. It is on by default for ARMv8 Thumb mode.
.. option:: -mtp=<arg>
Thread pointer access method (AArch32/AArch64 only)
.. option:: -munaligned-access, -mno-unaligned-access
Allow memory accesses to be unaligned (AArch32/AArch64 only)
Hexagon
-------
.. option:: -mieee-rnd-near
.. option:: -mmemops, -mno-memops
Enable generation of memop instructions
.. option:: -mnvj, -mno-nvj
Enable generation of new-value jumps
.. option:: -mnvs, -mno-nvs
Enable generation of new-value stores
.. option:: -mpackets, -mno-packets
Enable generation of instruction packets
Hexagon
-------
.. option:: -mhvx, -mno-hvx
Enable Hexagon Vector eXtensions
.. option:: -mhvx-length=<arg>
Set Hexagon Vector Length
.. program:: clang1
.. option:: -mhvx=<arg>
.. program:: clang
Enable Hexagon Vector eXtensions
M68k
----
.. option:: -ffixed-a0
Reserve the a0 register (M68k only)
.. option:: -ffixed-a1
Reserve the a1 register (M68k only)
.. option:: -ffixed-a2
Reserve the a2 register (M68k only)
.. option:: -ffixed-a3
Reserve the a3 register (M68k only)
.. option:: -ffixed-a4
Reserve the a4 register (M68k only)
.. option:: -ffixed-a5
Reserve the a5 register (M68k only)
.. option:: -ffixed-a6
Reserve the a6 register (M68k only)
.. option:: -ffixed-d0
Reserve the d0 register (M68k only)
.. option:: -ffixed-d1
Reserve the d1 register (M68k only)
.. option:: -ffixed-d2
Reserve the d2 register (M68k only)
.. option:: -ffixed-d3
Reserve the d3 register (M68k only)
.. option:: -ffixed-d4
Reserve the d4 register (M68k only)
.. option:: -ffixed-d5
Reserve the d5 register (M68k only)
.. option:: -ffixed-d6
Reserve the d6 register (M68k only)
.. option:: -ffixed-d7
Reserve the d7 register (M68k only)
.. option:: -m68000
.. option:: -m68010
.. option:: -m68020
.. option:: -m68030
.. option:: -m68040
.. option:: -m68060
MIPS
----
.. option:: -mabicalls, -mno-abicalls
Enable SVR4-style position-independent code (Mips only)
.. option:: -mabs=<arg>
.. option:: -mcheck-zero-division, -mno-check-zero-division
.. option:: -mcompact-branches=<arg>
.. option:: -mdouble-float
.. option:: -mdsp, -mno-dsp
.. option:: -mdspr2, -mno-dspr2
.. option:: -membedded-data, -mno-embedded-data
Place constants in the .rodata section instead of the .sdata section even if they meet the -G <size> threshold (MIPS)
.. option:: -mextern-sdata, -mno-extern-sdata
Assume that externally defined data is in the small data if it meets the -G <size> threshold (MIPS)
.. option:: -mfp32
Use 32-bit floating point registers (MIPS only)
.. option:: -mfp64
Use 64-bit floating point registers (MIPS only)
.. option:: -mginv, -mno-ginv
.. option:: -mgpopt, -mno-gpopt
Use GP relative accesses for symbols known to be in a small data section (MIPS)
.. option:: -mindirect-jump=<arg>
Change indirect jump instructions to inhibit speculation
.. option:: -mips16
.. option:: -mldc1-sdc1, -mno-ldc1-sdc1
.. option:: -mlocal-sdata, -mno-local-sdata
Extend the -G behaviour to object local data (MIPS)
.. option:: -mmadd4, -mno-madd4
Enable the generation of 4-operand madd.s, madd.d and related instructions.
.. option:: -mmicromips, -mno-micromips
.. option:: -mmsa, -mno-msa
Enable MSA ASE (MIPS only)
.. option:: -mmt, -mno-mt
Enable MT ASE (MIPS only)
.. option:: -mnan=<arg>
.. option:: -mno-mips16
.. option:: -msingle-float
.. option:: -mvirt, -mno-virt
.. option:: -mxgot, -mno-xgot
PowerPC
-------
.. option:: -maltivec, -mno-altivec
.. option:: -mcmpb, -mno-cmpb
.. option:: -mcrbits, -mno-crbits
.. option:: -mcrypto, -mno-crypto
.. option:: -mdirect-move, -mno-direct-move
.. option:: -mefpu2
.. option:: -mfloat128, -mno-float128
.. option:: -mfprnd, -mno-fprnd
.. option:: -mhtm, -mno-htm
.. option:: -minvariant-function-descriptors, -mno-invariant-function-descriptors
.. option:: -misel, -mno-isel
.. option:: -mlongcall, -mno-longcall
.. option:: -mmfocrf, -mmfcrf, -mno-mfocrf
.. option:: -mmma, -mno-mma
.. option:: -mpaired-vector-memops, -mno-paired-vector-memops
.. option:: -mpcrel, -mno-pcrel
.. option:: -mpopcntd, -mno-popcntd
.. option:: -mpower10-vector, -mno-power10-vector
.. option:: -mpower8-vector, -mno-power8-vector
.. option:: -mpower9-vector, -mno-power9-vector
.. option:: -mprefixed, -mno-prefixed
.. option:: -mprivileged
.. option:: -mrop-protect
.. option:: -msecure-plt
.. option:: -mspe, -mno-spe
.. option:: -mvsx, -mno-vsx
WebAssembly
-----------
.. option:: -matomics, -mno-atomics
.. option:: -mbulk-memory, -mno-bulk-memory
.. option:: -mexception-handling, -mno-exception-handling
.. option:: -mmultivalue, -mno-multivalue
.. option:: -mmutable-globals, -mno-mutable-globals
.. option:: -mnontrapping-fptoint, -mno-nontrapping-fptoint
.. option:: -mreference-types, -mno-reference-types
.. option:: -msign-ext, -mno-sign-ext
.. option:: -msimd128, -mno-simd128
.. option:: -mtail-call, -mno-tail-call
WebAssembly Driver
------------------
.. option:: -mexec-model=<arg>
Execution model (WebAssembly only)
X86
---
.. option:: -m3dnow, -mno-3dnow
.. option:: -m3dnowa, -mno-3dnowa
.. option:: -madx, -mno-adx
.. option:: -maes, -mno-aes
.. option:: -mamx-bf16, -mno-amx-bf16
.. option:: -mamx-int8, -mno-amx-int8
.. option:: -mamx-tile, -mno-amx-tile
.. option:: -mavx, -mno-avx
.. option:: -mavx2, -mno-avx2
.. option:: -mavx512bf16, -mno-avx512bf16
.. option:: -mavx512bitalg, -mno-avx512bitalg
.. option:: -mavx512bw, -mno-avx512bw
.. option:: -mavx512cd, -mno-avx512cd
.. option:: -mavx512dq, -mno-avx512dq
.. option:: -mavx512er, -mno-avx512er
.. option:: -mavx512f, -mno-avx512f
+.. option:: -mavx512fp16, -mno-avx512fp16
+
.. option:: -mavx512ifma, -mno-avx512ifma
.. option:: -mavx512pf, -mno-avx512pf
.. option:: -mavx512vbmi, -mno-avx512vbmi
.. option:: -mavx512vbmi2, -mno-avx512vbmi2
.. option:: -mavx512vl, -mno-avx512vl
.. option:: -mavx512vnni, -mno-avx512vnni
.. option:: -mavx512vp2intersect, -mno-avx512vp2intersect
.. option:: -mavx512vpopcntdq, -mno-avx512vpopcntdq
.. option:: -mavxvnni, -mno-avxvnni
.. option:: -mbmi, -mno-bmi
.. option:: -mbmi2, -mno-bmi2
.. option:: -mcldemote, -mno-cldemote
.. option:: -mclflushopt, -mno-clflushopt
.. option:: -mclwb, -mno-clwb
.. option:: -mclzero, -mno-clzero
.. option:: -mcx16, -mno-cx16
.. option:: -menqcmd, -mno-enqcmd
.. option:: -mf16c, -mno-f16c
.. option:: -mfma, -mno-fma
.. option:: -mfma4, -mno-fma4
.. option:: -mfsgsbase, -mno-fsgsbase
.. option:: -mfxsr, -mno-fxsr
.. option:: -mgfni, -mno-gfni
.. option:: -mhreset, -mno-hreset
.. option:: -minvpcid, -mno-invpcid
.. option:: -mkl, -mno-kl
.. option:: -mlwp, -mno-lwp
.. option:: -mlzcnt, -mno-lzcnt
.. option:: -mmmx, -mno-mmx
.. option:: -mmovbe, -mno-movbe
.. option:: -mmovdir64b, -mno-movdir64b
.. option:: -mmovdiri, -mno-movdiri
.. option:: -mmwaitx, -mno-mwaitx
.. option:: -mpclmul, -mno-pclmul
.. option:: -mpconfig, -mno-pconfig
.. option:: -mpku, -mno-pku
.. option:: -mpopcnt, -mno-popcnt
.. option:: -mprefetchwt1, -mno-prefetchwt1
.. option:: -mprfchw, -mno-prfchw
.. option:: -mptwrite, -mno-ptwrite
.. option:: -mrdpid, -mno-rdpid
.. option:: -mrdrnd, -mno-rdrnd
.. option:: -mrdseed, -mno-rdseed
.. option:: -mretpoline-external-thunk, -mno-retpoline-external-thunk
.. option:: -mrtm, -mno-rtm
.. option:: -msahf, -mno-sahf
.. option:: -mserialize, -mno-serialize
.. option:: -msgx, -mno-sgx
.. option:: -msha, -mno-sha
.. option:: -mshstk, -mno-shstk
.. option:: -msse, -mno-sse
.. option:: -msse2, -mno-sse2
.. option:: -msse3, -mno-sse3
.. option:: -msse4.1, -mno-sse4.1
.. program:: clang1
.. option:: -msse4.2, -mno-sse4.2, -msse4
.. program:: clang
.. option:: -msse4a, -mno-sse4a
.. option:: -mssse3, -mno-ssse3
.. option:: -mtbm, -mno-tbm
.. option:: -mtsxldtrk, -mno-tsxldtrk
.. option:: -muintr, -mno-uintr
.. option:: -mvaes, -mno-vaes
.. option:: -mvpclmulqdq, -mno-vpclmulqdq
.. option:: -mvzeroupper, -mno-vzeroupper
.. option:: -mwaitpkg, -mno-waitpkg
.. option:: -mwbnoinvd, -mno-wbnoinvd
.. option:: -mwidekl, -mno-widekl
.. option:: -mx87, -m80387, -mno-x87
.. option:: -mxop, -mno-xop
.. option:: -mxsave, -mno-xsave
.. option:: -mxsavec, -mno-xsavec
.. option:: -mxsaveopt, -mno-xsaveopt
.. option:: -mxsaves, -mno-xsaves
RISCV
-----
.. option:: -msave-restore, -mno-save-restore
Enable using library calls for save and restore
Long double flags
-----------------
Selects the long double implementation
.. option:: -mlong-double-128
Force long double to be 128 bits
.. option:: -mlong-double-64
Force long double to be 64 bits
.. option:: -mlong-double-80
Force long double to be 80 bits, padded to 128 bits for storage
Optimization level
~~~~~~~~~~~~~~~~~~
Flags controlling how much optimization should be performed.
.. option:: -O<arg>, -O (equivalent to -O1), --optimize, --optimize=<arg>
.. option:: -Ofast<arg>
Debug information generation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Flags controlling how much and what kind of debug information should be
generated.
Kind and level of debug information
-----------------------------------
.. option:: -g, --debug, --debug=<arg>
Generate source-level debug information
.. option:: -gdwarf
Generate source-level debug information with the default dwarf version
.. option:: -gdwarf-2
Generate source-level debug information with dwarf version 2
.. option:: -gdwarf-3
Generate source-level debug information with dwarf version 3
.. option:: -gdwarf-4
Generate source-level debug information with dwarf version 4
.. option:: -gdwarf-5
Generate source-level debug information with dwarf version 5
.. option:: -gdwarf32
Enables DWARF32 format for ELF binaries, if debug information emission is enabled.
.. option:: -gdwarf64
Enables DWARF64 format for ELF binaries, if debug information emission is enabled.
.. option:: -gfull
.. option:: -ginline-line-tables, -gno-inline-line-tables
.. option:: -gused
Debug level
___________
.. option:: -g0
.. option:: -g2
.. option:: -g3
.. option:: -ggdb0
.. option:: -ggdb1
.. option:: -ggdb2
.. option:: -ggdb3
.. option:: -gline-directives-only
Emit debug line info directives only
.. option:: -gline-tables-only, -g1, -gmlt
Emit debug line number tables only
.. option:: -gmodules
Generate debug info with external references to clang modules or precompiled headers
Debugger to tune debug information for
______________________________________
.. option:: -gdbx
.. option:: -ggdb
.. option:: -glldb
.. option:: -gsce
Debug information flags
-----------------------
.. option:: -gcolumn-info, -gno-column-info
.. option:: -gdwarf-aranges
.. option:: -gembed-source, -gno-embed-source
Embed source text in DWARF debug sections
.. option:: -ggnu-pubnames, -gno-gnu-pubnames
.. option:: -gpubnames, -gno-pubnames
.. option:: -grecord-command-line, -gno-record-command-line, -grecord-gcc-switches
.. option:: -gsplit-dwarf, -gno-split-dwarf
.. program:: clang1
.. option:: -gsplit-dwarf=<arg>
.. program:: clang
Set DWARF fission mode to either 'split' or 'single'
.. option:: -gstrict-dwarf, -gno-strict-dwarf
.. option:: -gz=<arg>, -gz (equivalent to -gz=zlib)
DWARF debug sections compression type
Static analyzer flags
=====================
Flags controlling the behavior of the Clang Static Analyzer.
.. option:: -Xanalyzer <arg>
Pass <arg> to the static analyzer
Fortran compilation flags
=========================
Flags that will be passed onto the ``gfortran`` compiler when Clang is given
a Fortran input.
.. option:: -A<arg>, --assert <arg>, --assert=<arg>
.. option:: -A-<arg>
.. option:: -faggressive-function-elimination, -fno-aggressive-function-elimination
.. option:: -falign-commons, -fno-align-commons
.. option:: -fall-intrinsics, -fno-all-intrinsics
.. option:: -fautomatic, -fno-automatic
.. option:: -fbacktrace, -fno-backtrace
.. option:: -fblas-matmul-limit=<arg>
.. option:: -fbounds-check, -fno-bounds-check
.. option:: -fcheck-array-temporaries, -fno-check-array-temporaries
.. option:: -fcheck=<arg>
.. option:: -fcoarray=<arg>
.. option:: -fconvert=<arg>
.. option:: -fcray-pointer, -fno-cray-pointer
.. option:: -fd-lines-as-code, -fno-d-lines-as-code
.. option:: -fd-lines-as-comments, -fno-d-lines-as-comments
.. option:: -fdollar-ok, -fno-dollar-ok
.. option:: -fdump-fortran-optimized, -fno-dump-fortran-optimized
.. option:: -fdump-fortran-original, -fno-dump-fortran-original
.. option:: -fdump-parse-tree, -fno-dump-parse-tree
.. option:: -fexternal-blas, -fno-external-blas
.. option:: -ff2c, -fno-f2c
.. option:: -ffpe-trap=<arg>
.. option:: -ffree-line-length-<arg>
.. option:: -ffrontend-optimize, -fno-frontend-optimize
.. option:: -finit-character=<arg>
.. option:: -finit-integer=<arg>
.. option:: -finit-local-zero, -fno-init-local-zero
.. option:: -finit-logical=<arg>
.. option:: -finit-real=<arg>
.. option:: -finteger-4-integer-8, -fno-integer-4-integer-8
.. option:: -fmax-array-constructor=<arg>
.. option:: -fmax-errors=<arg>
.. option:: -fmax-identifier-length, -fno-max-identifier-length
.. option:: -fmax-stack-var-size=<arg>
.. option:: -fmax-subrecord-length=<arg>
.. option:: -fmodule-private, -fno-module-private
.. option:: -fpack-derived, -fno-pack-derived
.. option:: -fprotect-parens, -fno-protect-parens
.. option:: -frange-check, -fno-range-check
.. option:: -freal-4-real-10, -fno-real-4-real-10
.. option:: -freal-4-real-16, -fno-real-4-real-16
.. option:: -freal-4-real-8, -fno-real-4-real-8
.. option:: -freal-8-real-10, -fno-real-8-real-10
.. option:: -freal-8-real-16, -fno-real-8-real-16
.. option:: -freal-8-real-4, -fno-real-8-real-4
.. option:: -frealloc-lhs, -fno-realloc-lhs
.. option:: -frecord-marker=<arg>
.. option:: -frecursive, -fno-recursive
.. option:: -frepack-arrays, -fno-repack-arrays
.. option:: -fsecond-underscore, -fno-second-underscore
.. option:: -fsign-zero, -fno-sign-zero
.. option:: -fstack-arrays, -fno-stack-arrays
.. option:: -funderscoring, -fno-underscoring
.. option:: -fwhole-file, -fno-whole-file
.. option:: -imultilib <arg>
.. option:: -static-libgfortran
Linker flags
============
Flags that are passed on to the linker
.. option:: -L<dir>, --library-directory <arg>, --library-directory=<arg>
Add directory to library search path
.. option:: -Mach
.. option:: -T<script>
Specify <script> as linker script
.. option:: -Tbss<addr>
Set starting address of BSS to <addr>
.. option:: -Tdata<addr>
Set starting address of DATA to <addr>
.. option:: -Ttext<addr>
Set starting address of TEXT to <addr>
.. option:: -Wl,<arg>,<arg2>...
Pass the comma separated arguments in <arg> to the linker
.. option:: -X
.. option:: -Xlinker <arg>, --for-linker <arg>, --for-linker=<arg>
Pass <arg> to the linker
.. program:: clang1
.. option:: -Z
.. program:: clang
.. option:: -coverage, --coverage
.. option:: -e<arg>, --entry
.. option:: -filelist <arg>
.. option:: --hip-device-lib=<arg>
HIP device library
.. option:: -l<arg>
.. option:: --ld-path=<arg>
.. option:: -nostartfiles
.. program:: clang1
.. option:: -nostdlib, --no-standard-libraries
.. program:: clang
.. option:: -pie
.. option:: -r
.. option:: -rdynamic
.. option:: --rocm-device-lib-path=<arg>, --hip-device-lib-path=<arg>
ROCm device library path. Alternative to rocm-path.
.. option:: -rpath <arg>
.. option:: -s
.. option:: -shared, --shared
.. option:: -specs=<arg>, --specs=<arg>
.. option:: -static, --static
.. option:: -static-pie
.. option:: -t
.. option:: -u<arg>, --force-link <arg>, --force-link=<arg>
.. option:: -undef
undef all system defines
.. option:: -undefined<arg>, --no-undefined
.. option:: -z <arg>
Pass -z <arg> to the linker
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 6ced38dd2fae..087aa66c1b7a 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -1,4071 +1,4072 @@
=========================
Clang Language Extensions
=========================
.. contents::
:local:
:depth: 1
.. toctree::
:hidden:
ObjectiveCLiterals
BlockLanguageSpec
Block-ABI-Apple
AutomaticReferenceCounting
MatrixTypes
Introduction
============
This document describes the language extensions provided by Clang. In addition
to the language extensions listed here, Clang aims to support a broad range of
GCC extensions. Please see the `GCC manual
<https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html>`_ for more information on
these extensions.
.. _langext-feature_check:
Feature Checking Macros
=======================
Language extensions can be very useful, but only if you know you can depend on
them. In order to allow fine-grain features checks, we support three builtin
function-like macros. This allows you to directly test for a feature in your
code without having to resort to something like autoconf or fragile "compiler
version checks".
``__has_builtin``
-----------------
This function-like macro takes a single identifier argument that is the name of
a builtin function, a builtin pseudo-function (taking one or more type
arguments), or a builtin template.
It evaluates to 1 if the builtin is supported or 0 if not.
It can be used like this:
.. code-block:: c++
#ifndef __has_builtin // Optional of course.
#define __has_builtin(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_builtin(__builtin_trap)
__builtin_trap();
#else
abort();
#endif
...
.. note::
Prior to Clang 10, ``__has_builtin`` could not be used to detect most builtin
pseudo-functions.
``__has_builtin`` should not be used to detect support for a builtin macro;
use ``#ifdef`` instead.
.. _langext-__has_feature-__has_extension:
``__has_feature`` and ``__has_extension``
-----------------------------------------
These function-like macros take a single identifier argument that is the name
of a feature. ``__has_feature`` evaluates to 1 if the feature is both
supported by Clang and standardized in the current language standard or 0 if
not (but see :ref:`below <langext-has-feature-back-compat>`), while
``__has_extension`` evaluates to 1 if the feature is supported by Clang in the
current language (either as a language extension or a standard language
feature) or 0 if not. They can be used like this:
.. code-block:: c++
#ifndef __has_feature // Optional of course.
#define __has_feature(x) 0 // Compatibility with non-clang compilers.
#endif
#ifndef __has_extension
#define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
#endif
...
#if __has_feature(cxx_rvalue_references)
// This code will only be compiled with the -std=c++11 and -std=gnu++11
// options, because rvalue references are only standardized in C++11.
#endif
#if __has_extension(cxx_rvalue_references)
// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
// and -std=gnu++98 options, because rvalue references are supported as a
// language extension in C++98.
#endif
.. _langext-has-feature-back-compat:
For backward compatibility, ``__has_feature`` can also be used to test
for support for non-standardized features, i.e. features not prefixed ``c_``,
``cxx_`` or ``objc_``.
Another use of ``__has_feature`` is to check for compiler features not related
to the language standard, such as e.g. :doc:`AddressSanitizer
<AddressSanitizer>`.
If the ``-pedantic-errors`` option is given, ``__has_extension`` is equivalent
to ``__has_feature``.
The feature tag is described along with the language feature below.
The feature name or extension name can also be specified with a preceding and
following ``__`` (double underscore) to avoid interference from a macro with
the same name. For instance, ``__cxx_rvalue_references__`` can be used instead
of ``cxx_rvalue_references``.
``__has_cpp_attribute``
-----------------------
This function-like macro is available in C++20 by default, and is provided as an
extension in earlier language standards. It takes a single argument that is the
name of a double-square-bracket-style attribute. The argument can either be a
single identifier or a scoped identifier. If the attribute is supported, a
nonzero value is returned. If the attribute is a standards-based attribute, this
macro returns a nonzero value based on the year and month in which the attribute
was voted into the working draft. See `WG21 SD-6
<https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations>`_
for the list of values returned for standards-based attributes. If the attribute
is not supported by the current compilation target, this macro evaluates to 0.
It can be used like this:
.. code-block:: c++
#ifndef __has_cpp_attribute // For backwards compatibility
#define __has_cpp_attribute(x) 0
#endif
...
#if __has_cpp_attribute(clang::fallthrough)
#define FALLTHROUGH [[clang::fallthrough]]
#else
#define FALLTHROUGH
#endif
...
The attribute scope tokens ``clang`` and ``_Clang`` are interchangeable, as are
the attribute scope tokens ``gnu`` and ``__gnu__``. Attribute tokens in either
of these namespaces can be specified with a preceding and following ``__``
(double underscore) to avoid interference from a macro with the same name. For
instance, ``gnu::__const__`` can be used instead of ``gnu::const``.
``__has_c_attribute``
---------------------
This function-like macro takes a single argument that is the name of an
attribute exposed with the double square-bracket syntax in C mode. The argument
can either be a single identifier or a scoped identifier. If the attribute is
supported, a nonzero value is returned. If the attribute is not supported by the
current compilation target, this macro evaluates to 0. It can be used like this:
.. code-block:: c
#ifndef __has_c_attribute // Optional of course.
#define __has_c_attribute(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_c_attribute(fallthrough)
#define FALLTHROUGH [[fallthrough]]
#else
#define FALLTHROUGH
#endif
...
The attribute scope tokens ``clang`` and ``_Clang`` are interchangeable, as are
the attribute scope tokens ``gnu`` and ``__gnu__``. Attribute tokens in either
of these namespaces can be specified with a preceding and following ``__``
(double underscore) to avoid interference from a macro with the same name. For
instance, ``gnu::__const__`` can be used instead of ``gnu::const``.
``__has_attribute``
-------------------
This function-like macro takes a single identifier argument that is the name of
a GNU-style attribute. It evaluates to 1 if the attribute is supported by the
current compilation target, or 0 if not. It can be used like this:
.. code-block:: c++
#ifndef __has_attribute // Optional of course.
#define __has_attribute(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_attribute(always_inline)
#define ALWAYS_INLINE __attribute__((always_inline))
#else
#define ALWAYS_INLINE
#endif
...
The attribute name can also be specified with a preceding and following ``__``
(double underscore) to avoid interference from a macro with the same name. For
instance, ``__always_inline__`` can be used instead of ``always_inline``.
``__has_declspec_attribute``
----------------------------
This function-like macro takes a single identifier argument that is the name of
an attribute implemented as a Microsoft-style ``__declspec`` attribute. It
evaluates to 1 if the attribute is supported by the current compilation target,
or 0 if not. It can be used like this:
.. code-block:: c++
#ifndef __has_declspec_attribute // Optional of course.
#define __has_declspec_attribute(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_declspec_attribute(dllexport)
#define DLLEXPORT __declspec(dllexport)
#else
#define DLLEXPORT
#endif
...
The attribute name can also be specified with a preceding and following ``__``
(double underscore) to avoid interference from a macro with the same name. For
instance, ``__dllexport__`` can be used instead of ``dllexport``.
``__is_identifier``
-------------------
This function-like macro takes a single identifier argument that might be either
a reserved word or a regular identifier. It evaluates to 1 if the argument is just
a regular identifier and not a reserved word, in the sense that it can then be
used as the name of a user-defined function or variable. Otherwise it evaluates
to 0. It can be used like this:
.. code-block:: c++
...
#ifdef __is_identifier // Compatibility with non-clang compilers.
#if __is_identifier(__wchar_t)
typedef wchar_t __wchar_t;
#endif
#endif
__wchar_t WideCharacter;
...
Include File Checking Macros
============================
Not all developments systems have the same include files. The
:ref:`langext-__has_include` and :ref:`langext-__has_include_next` macros allow
you to check for the existence of an include file before doing a possibly
failing ``#include`` directive. Include file checking macros must be used
as expressions in ``#if`` or ``#elif`` preprocessing directives.
.. _langext-__has_include:
``__has_include``
-----------------
This function-like macro takes a single file name string argument that is the
name of an include file. It evaluates to 1 if the file can be found using the
include paths, or 0 otherwise:
.. code-block:: c++
// Note the two possible file name string formats.
#if __has_include("myinclude.h") && __has_include(<stdint.h>)
# include "myinclude.h"
#endif
To test for this feature, use ``#if defined(__has_include)``:
.. code-block:: c++
// To avoid problem with non-clang compilers not having this macro.
#if defined(__has_include)
#if __has_include("myinclude.h")
# include "myinclude.h"
#endif
#endif
.. _langext-__has_include_next:
``__has_include_next``
----------------------
This function-like macro takes a single file name string argument that is the
name of an include file. It is like ``__has_include`` except that it looks for
the second instance of the given file found in the include paths. It evaluates
to 1 if the second instance of the file can be found using the include paths,
or 0 otherwise:
.. code-block:: c++
// Note the two possible file name string formats.
#if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>)
# include_next "myinclude.h"
#endif
// To avoid problem with non-clang compilers not having this macro.
#if defined(__has_include_next)
#if __has_include_next("myinclude.h")
# include_next "myinclude.h"
#endif
#endif
Note that ``__has_include_next``, like the GNU extension ``#include_next``
directive, is intended for use in headers only, and will issue a warning if
used in the top-level compilation file. A warning will also be issued if an
absolute path is used in the file argument.
``__has_warning``
-----------------
This function-like macro takes a string literal that represents a command line
option for a warning and returns true if that is a valid warning option.
.. code-block:: c++
#if __has_warning("-Wformat")
...
#endif
.. _languageextensions-builtin-macros:
Builtin Macros
==============
``__BASE_FILE__``
Defined to a string that contains the name of the main input file passed to
Clang.
``__FILE_NAME__``
Clang-specific extension that functions similar to ``__FILE__`` but only
renders the last path component (the filename) instead of an invocation
dependent full path to that file.
``__COUNTER__``
Defined to an integer value that starts at zero and is incremented each time
the ``__COUNTER__`` macro is expanded.
``__INCLUDE_LEVEL__``
Defined to an integral value that is the include depth of the file currently
being translated. For the main file, this value is zero.
``__TIMESTAMP__``
Defined to the date and time of the last modification of the current source
file.
``__clang__``
Defined when compiling with Clang
``__clang_major__``
Defined to the major marketing version number of Clang (e.g., the 2 in
2.0.1). Note that marketing version numbers should not be used to check for
language features, as different vendors use different numbering schemes.
Instead, use the :ref:`langext-feature_check`.
``__clang_minor__``
Defined to the minor version number of Clang (e.g., the 0 in 2.0.1). Note
that marketing version numbers should not be used to check for language
features, as different vendors use different numbering schemes. Instead, use
the :ref:`langext-feature_check`.
``__clang_patchlevel__``
Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).
``__clang_version__``
Defined to a string that captures the Clang marketing version, including the
Subversion tag or revision number, e.g., "``1.5 (trunk 102332)``".
``__clang_literal_encoding__``
Defined to a narrow string literal that represents the current encoding of
narrow string literals, e.g., ``"hello"``. This macro typically expands to
"UTF-8" (but may change in the future if the
``-fexec-charset="Encoding-Name"`` option is implemented.)
``__clang_wide_literal_encoding__``
Defined to a narrow string literal that represents the current encoding of
wide string literals, e.g., ``L"hello"``. This macro typically expands to
"UTF-16" or "UTF-32" (but may change in the future if the
``-fwide-exec-charset="Encoding-Name"`` option is implemented.)
.. _langext-vectors:
Vectors and Extended Vectors
============================
Supports the GCC, OpenCL, AltiVec and NEON vector extensions.
OpenCL vector types are created using the ``ext_vector_type`` attribute. It
supports the ``V.xyzw`` syntax and other tidbits as seen in OpenCL. An example
is:
.. code-block:: c++
typedef float float4 __attribute__((ext_vector_type(4)));
typedef float float2 __attribute__((ext_vector_type(2)));
float4 foo(float2 a, float2 b) {
float4 c;
c.xz = a;
c.yw = b;
return c;
}
Query for this feature with ``__has_attribute(ext_vector_type)``.
Giving ``-maltivec`` option to clang enables support for AltiVec vector syntax
and functions. For example:
.. code-block:: c++
vector float foo(vector int a) {
vector int b;
b = vec_add(a, a) + a;
return (vector float)b;
}
NEON vector types are created using ``neon_vector_type`` and
``neon_polyvector_type`` attributes. For example:
.. code-block:: c++
typedef __attribute__((neon_vector_type(8))) int8_t int8x8_t;
typedef __attribute__((neon_polyvector_type(16))) poly8_t poly8x16_t;
int8x8_t foo(int8x8_t a) {
int8x8_t v;
v = a;
return v;
}
Vector Literals
---------------
Vector literals can be used to create vectors from a set of scalars, or
vectors. Either parentheses or braces form can be used. In the parentheses
form the number of literal values specified must be one, i.e. referring to a
scalar value, or must match the size of the vector type being created. If a
single scalar literal value is specified, the scalar literal value will be
replicated to all the components of the vector type. In the brackets form any
number of literals can be specified. For example:
.. code-block:: c++
typedef int v4si __attribute__((__vector_size__(16)));
typedef float float4 __attribute__((ext_vector_type(4)));
typedef float float2 __attribute__((ext_vector_type(2)));
v4si vsi = (v4si){1, 2, 3, 4};
float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
vector int vi3 = (vector int)(1, 2); // error
vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
vector int vi5 = (vector int)(1, 2, 3, 4);
float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
Vector Operations
-----------------
The table below shows the support for each operation by vector extension. A
dash indicates that an operation is not accepted according to a corresponding
specification.
============================== ======= ======= ============= =======
Operator OpenCL AltiVec GCC NEON
============================== ======= ======= ============= =======
[] yes yes yes --
unary operators +, -- yes yes yes --
++, -- -- yes yes yes --
+,--,*,/,% yes yes yes --
bitwise operators &,|,^,~ yes yes yes --
>>,<< yes yes yes --
!, &&, || yes -- yes --
==, !=, >, <, >=, <= yes yes yes --
= yes yes yes yes
?: [#]_ yes -- yes --
sizeof yes yes yes yes
C-style cast yes yes yes no
reinterpret_cast yes no yes no
static_cast yes no yes no
const_cast no no no no
============================== ======= ======= ============= =======
See also :ref:`langext-__builtin_shufflevector`, :ref:`langext-__builtin_convertvector`.
.. [#] ternary operator(?:) has different behaviors depending on condition
operand's vector type. If the condition is a GNU vector (i.e. __vector_size__),
it's only available in C++ and uses normal bool conversions (that is, != 0).
If it's an extension (OpenCL) vector, it's only available in C and OpenCL C.
And it selects base on signedness of the condition operands (OpenCL v1.1 s6.3.9).
Matrix Types
============
Clang provides an extension for matrix types, which is currently being
implemented. See :ref:`the draft specification <matrixtypes>` for more details.
For example, the code below uses the matrix types extension to multiply two 4x4
float matrices and add the result to a third 4x4 matrix.
.. code-block:: c++
typedef float m4x4_t __attribute__((matrix_type(4, 4)));
m4x4_t f(m4x4_t a, m4x4_t b, m4x4_t c) {
return a + b * c;
}
The matrix type extension also supports operations on a matrix and a scalar.
.. code-block:: c++
typedef float m4x4_t __attribute__((matrix_type(4, 4)));
m4x4_t f(m4x4_t a) {
return (a + 23) * 12;
}
The matrix type extension supports division on a matrix and a scalar but not on a matrix and a matrix.
.. code-block:: c++
typedef float m4x4_t __attribute__((matrix_type(4, 4)));
m4x4_t f(m4x4_t a) {
a = a / 3.0;
return a;
}
The matrix type extension supports compound assignments for addition, subtraction, and multiplication on matrices
and on a matrix and a scalar, provided their types are consistent.
.. code-block:: c++
typedef float m4x4_t __attribute__((matrix_type(4, 4)));
m4x4_t f(m4x4_t a, m4x4_t b) {
a += b;
a -= b;
a *= b;
a += 23;
a -= 12;
return a;
}
The matrix type extension supports explicit casts. Implicit type conversion between matrix types is not allowed.
.. code-block:: c++
typedef int ix5x5 __attribute__((matrix_type(5, 5)));
typedef float fx5x5 __attribute__((matrix_type(5, 5)));
fx5x5 f1(ix5x5 i, fx5x5 f) {
return (fx5x5) i;
}
template <typename X>
using matrix_4_4 = X __attribute__((matrix_type(4, 4)));
void f2() {
matrix_5_5<double> d;
matrix_5_5<int> i;
i = (matrix_5_5<int>)d;
i = static_cast<matrix_5_5<int>>(d);
}
Half-Precision Floating Point
=============================
Clang supports three half-precision (16-bit) floating point types: ``__fp16``,
``_Float16`` and ``__bf16``. These types are supported in all language modes.
``__fp16`` is supported on every target, as it is purely a storage format; see below.
``_Float16`` is currently only supported on the following targets, with further
targets pending ABI standardization:
* 32-bit ARM
* 64-bit ARM (AArch64)
* AMDGPU
* SPIR
+* X86 (Only available under feature AVX512-FP16)
``_Float16`` will be supported on more targets as they define ABIs for it.
``__bf16`` is purely a storage format; it is currently only supported on the following targets:
* 32-bit ARM
* 64-bit ARM (AArch64)
The ``__bf16`` type is only available when supported in hardware.
``__fp16`` is a storage and interchange format only. This means that values of
``__fp16`` are immediately promoted to (at least) ``float`` when used in arithmetic
operations, so that e.g. the result of adding two ``__fp16`` values has type ``float``.
The behavior of ``__fp16`` is specified by the ARM C Language Extensions (`ACLE <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053d/IHI0053D_acle_2_1.pdf>`_).
Clang uses the ``binary16`` format from IEEE 754-2008 for ``__fp16``, not the ARM
alternative format.
``_Float16`` is an interchange floating-point type. This means that, just like arithmetic on
``float`` or ``double``, arithmetic on ``_Float16`` operands is formally performed in the
``_Float16`` type, so that e.g. the result of adding two ``_Float16`` values has type
``_Float16``. The behavior of ``_Float16`` is specified by ISO/IEC TS 18661-3:2015
("Floating-point extensions for C"). As with ``__fp16``, Clang uses the ``binary16``
format from IEEE 754-2008 for ``_Float16``.
``_Float16`` arithmetic will be performed using native half-precision support
when available on the target (e.g. on ARMv8.2a); otherwise it will be performed
at a higher precision (currently always ``float``) and then truncated down to
``_Float16``. Note that C and C++ allow intermediate floating-point operands
of an expression to be computed with greater precision than is expressible in
their type, so Clang may avoid intermediate truncations in certain cases; this may
lead to results that are inconsistent with native arithmetic.
It is recommended that portable code use ``_Float16`` instead of ``__fp16``,
as it has been defined by the C standards committee and has behavior that is
more familiar to most programmers.
Because ``__fp16`` operands are always immediately promoted to ``float``, the
common real type of ``__fp16`` and ``_Float16`` for the purposes of the usual
arithmetic conversions is ``float``.
A literal can be given ``_Float16`` type using the suffix ``f16``. For example,
``3.14f16``.
Because default argument promotion only applies to the standard floating-point
types, ``_Float16`` values are not promoted to ``double`` when passed as variadic
or untyped arguments. As a consequence, some caution must be taken when using
certain library facilities with ``_Float16``; for example, there is no ``printf`` format
specifier for ``_Float16``, and (unlike ``float``) it will not be implicitly promoted to
``double`` when passed to ``printf``, so the programmer must explicitly cast it to
``double`` before using it with an ``%f`` or similar specifier.
Messages on ``deprecated`` and ``unavailable`` Attributes
=========================================================
An optional string message can be added to the ``deprecated`` and
``unavailable`` attributes. For example:
.. code-block:: c++
void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));
If the deprecated or unavailable declaration is used, the message will be
incorporated into the appropriate diagnostic:
.. code-block:: none
harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!!
[-Wdeprecated-declarations]
explode();
^
Query for this feature with
``__has_extension(attribute_deprecated_with_message)`` and
``__has_extension(attribute_unavailable_with_message)``.
Attributes on Enumerators
=========================
Clang allows attributes to be written on individual enumerators. This allows
enumerators to be deprecated, made unavailable, etc. The attribute must appear
after the enumerator name and before any initializer, like so:
.. code-block:: c++
enum OperationMode {
OM_Invalid,
OM_Normal,
OM_Terrified __attribute__((deprecated)),
OM_AbortOnError __attribute__((deprecated)) = 4
};
Attributes on the ``enum`` declaration do not apply to individual enumerators.
Query for this feature with ``__has_extension(enumerator_attributes)``.
C++11 Attributes on using-declarations
======================================
Clang allows C++-style ``[[]]`` attributes to be written on using-declarations.
For instance:
.. code-block:: c++
[[clang::using_if_exists]] using foo::bar;
using foo::baz [[clang::using_if_exists]];
You can test for support for this extension with
``__has_extension(cxx_attributes_on_using_declarations)``.
'User-Specified' System Frameworks
==================================
Clang provides a mechanism by which frameworks can be built in such a way that
they will always be treated as being "system frameworks", even if they are not
present in a system framework directory. This can be useful to system
framework developers who want to be able to test building other applications
with development builds of their framework, including the manner in which the
compiler changes warning behavior for system headers.
Framework developers can opt-in to this mechanism by creating a
"``.system_framework``" file at the top-level of their framework. That is, the
framework should have contents like:
.. code-block:: none
.../TestFramework.framework
.../TestFramework.framework/.system_framework
.../TestFramework.framework/Headers
.../TestFramework.framework/Headers/TestFramework.h
...
Clang will treat the presence of this file as an indicator that the framework
should be treated as a system framework, regardless of how it was found in the
framework search path. For consistency, we recommend that such files never be
included in installed versions of the framework.
Checks for Standard Language Features
=====================================
The ``__has_feature`` macro can be used to query if certain standard language
features are enabled. The ``__has_extension`` macro can be used to query if
language features are available as an extension when compiling for a standard
which does not provide them. The features which can be tested are listed here.
Since Clang 3.4, the C++ SD-6 feature test macros are also supported.
These are macros with names of the form ``__cpp_<feature_name>``, and are
intended to be a portable way to query the supported features of the compiler.
See `the C++ status page <https://clang.llvm.org/cxx_status.html#ts>`_ for
information on the version of SD-6 supported by each Clang release, and the
macros provided by that revision of the recommendations.
C++98
-----
The features listed below are part of the C++98 standard. These features are
enabled by default when compiling C++ code.
C++ exceptions
^^^^^^^^^^^^^^
Use ``__has_feature(cxx_exceptions)`` to determine if C++ exceptions have been
enabled. For example, compiling code with ``-fno-exceptions`` disables C++
exceptions.
C++ RTTI
^^^^^^^^
Use ``__has_feature(cxx_rtti)`` to determine if C++ RTTI has been enabled. For
example, compiling code with ``-fno-rtti`` disables the use of RTTI.
C++11
-----
The features listed below are part of the C++11 standard. As a result, all
these features are enabled with the ``-std=c++11`` or ``-std=gnu++11`` option
when compiling C++ code.
C++11 SFINAE includes access control
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_access_control_sfinae)`` or
``__has_extension(cxx_access_control_sfinae)`` to determine whether
access-control errors (e.g., calling a private constructor) are considered to
be template argument deduction errors (aka SFINAE errors), per `C++ DR1170
<http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170>`_.
C++11 alias templates
^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_alias_templates)`` or
``__has_extension(cxx_alias_templates)`` to determine if support for C++11's
alias declarations and alias templates is enabled.
C++11 alignment specifiers
^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_alignas)`` or ``__has_extension(cxx_alignas)`` to
determine if support for alignment specifiers using ``alignas`` is enabled.
Use ``__has_feature(cxx_alignof)`` or ``__has_extension(cxx_alignof)`` to
determine if support for the ``alignof`` keyword is enabled.
C++11 attributes
^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_attributes)`` or ``__has_extension(cxx_attributes)`` to
determine if support for attribute parsing with C++11's square bracket notation
is enabled.
C++11 generalized constant expressions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_constexpr)`` to determine if support for generalized
constant expressions (e.g., ``constexpr``) is enabled.
C++11 ``decltype()``
^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_decltype)`` or ``__has_extension(cxx_decltype)`` to
determine if support for the ``decltype()`` specifier is enabled. C++11's
``decltype`` does not require type-completeness of a function call expression.
Use ``__has_feature(cxx_decltype_incomplete_return_types)`` or
``__has_extension(cxx_decltype_incomplete_return_types)`` to determine if
support for this feature is enabled.
C++11 default template arguments in function templates
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_default_function_template_args)`` or
``__has_extension(cxx_default_function_template_args)`` to determine if support
for default template arguments in function templates is enabled.
C++11 ``default``\ ed functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_defaulted_functions)`` or
``__has_extension(cxx_defaulted_functions)`` to determine if support for
defaulted function definitions (with ``= default``) is enabled.
C++11 delegating constructors
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_delegating_constructors)`` to determine if support for
delegating constructors is enabled.
C++11 ``deleted`` functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_deleted_functions)`` or
``__has_extension(cxx_deleted_functions)`` to determine if support for deleted
function definitions (with ``= delete``) is enabled.
C++11 explicit conversion functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_explicit_conversions)`` to determine if support for
``explicit`` conversion functions is enabled.
C++11 generalized initializers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_generalized_initializers)`` to determine if support for
generalized initializers (using braced lists and ``std::initializer_list``) is
enabled.
C++11 implicit move constructors/assignment operators
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_implicit_moves)`` to determine if Clang will implicitly
generate move constructors and move assignment operators where needed.
C++11 inheriting constructors
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_inheriting_constructors)`` to determine if support for
inheriting constructors is enabled.
C++11 inline namespaces
^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_inline_namespaces)`` or
``__has_extension(cxx_inline_namespaces)`` to determine if support for inline
namespaces is enabled.
C++11 lambdas
^^^^^^^^^^^^^
Use ``__has_feature(cxx_lambdas)`` or ``__has_extension(cxx_lambdas)`` to
determine if support for lambdas is enabled.
C++11 local and unnamed types as template arguments
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_local_type_template_args)`` or
``__has_extension(cxx_local_type_template_args)`` to determine if support for
local and unnamed types as template arguments is enabled.
C++11 noexcept
^^^^^^^^^^^^^^
Use ``__has_feature(cxx_noexcept)`` or ``__has_extension(cxx_noexcept)`` to
determine if support for noexcept exception specifications is enabled.
C++11 in-class non-static data member initialization
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_nonstatic_member_init)`` to determine whether in-class
initialization of non-static data members is enabled.
C++11 ``nullptr``
^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_nullptr)`` or ``__has_extension(cxx_nullptr)`` to
determine if support for ``nullptr`` is enabled.
C++11 ``override control``
^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_override_control)`` or
``__has_extension(cxx_override_control)`` to determine if support for the
override control keywords is enabled.
C++11 reference-qualified functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_reference_qualified_functions)`` or
``__has_extension(cxx_reference_qualified_functions)`` to determine if support
for reference-qualified functions (e.g., member functions with ``&`` or ``&&``
applied to ``*this``) is enabled.
C++11 range-based ``for`` loop
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_range_for)`` or ``__has_extension(cxx_range_for)`` to
determine if support for the range-based for loop is enabled.
C++11 raw string literals
^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_raw_string_literals)`` to determine if support for raw
string literals (e.g., ``R"x(foo\bar)x"``) is enabled.
C++11 rvalue references
^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_rvalue_references)`` or
``__has_extension(cxx_rvalue_references)`` to determine if support for rvalue
references is enabled.
C++11 ``static_assert()``
^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_static_assert)`` or
``__has_extension(cxx_static_assert)`` to determine if support for compile-time
assertions using ``static_assert`` is enabled.
C++11 ``thread_local``
^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_thread_local)`` to determine if support for
``thread_local`` variables is enabled.
C++11 type inference
^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_auto_type)`` or ``__has_extension(cxx_auto_type)`` to
determine C++11 type inference is supported using the ``auto`` specifier. If
this is disabled, ``auto`` will instead be a storage class specifier, as in C
or C++98.
C++11 strongly typed enumerations
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_strong_enums)`` or
``__has_extension(cxx_strong_enums)`` to determine if support for strongly
typed, scoped enumerations is enabled.
C++11 trailing return type
^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_trailing_return)`` or
``__has_extension(cxx_trailing_return)`` to determine if support for the
alternate function declaration syntax with trailing return type is enabled.
C++11 Unicode string literals
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_unicode_literals)`` to determine if support for Unicode
string literals is enabled.
C++11 unrestricted unions
^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_unrestricted_unions)`` to determine if support for
unrestricted unions is enabled.
C++11 user-defined literals
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_user_literals)`` to determine if support for
user-defined literals is enabled.
C++11 variadic templates
^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_variadic_templates)`` or
``__has_extension(cxx_variadic_templates)`` to determine if support for
variadic templates is enabled.
C++14
-----
The features listed below are part of the C++14 standard. As a result, all
these features are enabled with the ``-std=C++14`` or ``-std=gnu++14`` option
when compiling C++ code.
C++14 binary literals
^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_binary_literals)`` or
``__has_extension(cxx_binary_literals)`` to determine whether
binary literals (for instance, ``0b10010``) are recognized. Clang supports this
feature as an extension in all language modes.
C++14 contextual conversions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_contextual_conversions)`` or
``__has_extension(cxx_contextual_conversions)`` to determine if the C++14 rules
are used when performing an implicit conversion for an array bound in a
*new-expression*, the operand of a *delete-expression*, an integral constant
expression, or a condition in a ``switch`` statement.
C++14 decltype(auto)
^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_decltype_auto)`` or
``__has_extension(cxx_decltype_auto)`` to determine if support
for the ``decltype(auto)`` placeholder type is enabled.
C++14 default initializers for aggregates
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_aggregate_nsdmi)`` or
``__has_extension(cxx_aggregate_nsdmi)`` to determine if support
for default initializers in aggregate members is enabled.
C++14 digit separators
^^^^^^^^^^^^^^^^^^^^^^
Use ``__cpp_digit_separators`` to determine if support for digit separators
using single quotes (for instance, ``10'000``) is enabled. At this time, there
is no corresponding ``__has_feature`` name
C++14 generalized lambda capture
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_init_captures)`` or
``__has_extension(cxx_init_captures)`` to determine if support for
lambda captures with explicit initializers is enabled
(for instance, ``[n(0)] { return ++n; }``).
C++14 generic lambdas
^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_generic_lambdas)`` or
``__has_extension(cxx_generic_lambdas)`` to determine if support for generic
(polymorphic) lambdas is enabled
(for instance, ``[] (auto x) { return x + 1; }``).
C++14 relaxed constexpr
^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_relaxed_constexpr)`` or
``__has_extension(cxx_relaxed_constexpr)`` to determine if variable
declarations, local variable modification, and control flow constructs
are permitted in ``constexpr`` functions.
C++14 return type deduction
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_return_type_deduction)`` or
``__has_extension(cxx_return_type_deduction)`` to determine if support
for return type deduction for functions (using ``auto`` as a return type)
is enabled.
C++14 runtime-sized arrays
^^^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_runtime_array)`` or
``__has_extension(cxx_runtime_array)`` to determine if support
for arrays of runtime bound (a restricted form of variable-length arrays)
is enabled.
Clang's implementation of this feature is incomplete.
C++14 variable templates
^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(cxx_variable_templates)`` or
``__has_extension(cxx_variable_templates)`` to determine if support for
templated variable declarations is enabled.
C11
---
The features listed below are part of the C11 standard. As a result, all these
features are enabled with the ``-std=c11`` or ``-std=gnu11`` option when
compiling C code. Additionally, because these features are all
backward-compatible, they are available as extensions in all language modes.
C11 alignment specifiers
^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(c_alignas)`` or ``__has_extension(c_alignas)`` to determine
if support for alignment specifiers using ``_Alignas`` is enabled.
Use ``__has_feature(c_alignof)`` or ``__has_extension(c_alignof)`` to determine
if support for the ``_Alignof`` keyword is enabled.
C11 atomic operations
^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(c_atomic)`` or ``__has_extension(c_atomic)`` to determine
if support for atomic types using ``_Atomic`` is enabled. Clang also provides
:ref:`a set of builtins <langext-__c11_atomic>` which can be used to implement
the ``<stdatomic.h>`` operations on ``_Atomic`` types. Use
``__has_include(<stdatomic.h>)`` to determine if C11's ``<stdatomic.h>`` header
is available.
Clang will use the system's ``<stdatomic.h>`` header when one is available, and
will otherwise use its own. When using its own, implementations of the atomic
operations are provided as macros. In the cases where C11 also requires a real
function, this header provides only the declaration of that function (along
with a shadowing macro implementation), and you must link to a library which
provides a definition of the function if you use it instead of the macro.
C11 generic selections
^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(c_generic_selections)`` or
``__has_extension(c_generic_selections)`` to determine if support for generic
selections is enabled.
As an extension, the C11 generic selection expression is available in all
languages supported by Clang. The syntax is the same as that given in the C11
standard.
In C, type compatibility is decided according to the rules given in the
appropriate standard, but in C++, which lacks the type compatibility rules used
in C, types are considered compatible only if they are equivalent.
C11 ``_Static_assert()``
^^^^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(c_static_assert)`` or ``__has_extension(c_static_assert)``
to determine if support for compile-time assertions using ``_Static_assert`` is
enabled.
C11 ``_Thread_local``
^^^^^^^^^^^^^^^^^^^^^
Use ``__has_feature(c_thread_local)`` or ``__has_extension(c_thread_local)``
to determine if support for ``_Thread_local`` variables is enabled.
Modules
-------
Use ``__has_feature(modules)`` to determine if Modules have been enabled.
For example, compiling code with ``-fmodules`` enables the use of Modules.
More information could be found `here <https://clang.llvm.org/docs/Modules.html>`_.
Type Trait Primitives
=====================
Type trait primitives are special builtin constant expressions that can be used
by the standard C++ library to facilitate or simplify the implementation of
user-facing type traits in the <type_traits> header.
They are not intended to be used directly by user code because they are
implementation-defined and subject to change -- as such they're tied closely to
the supported set of system headers, currently:
* LLVM's own libc++
* GNU libstdc++
* The Microsoft standard C++ library
Clang supports the `GNU C++ type traits
<https://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>`_ and a subset of the
`Microsoft Visual C++ type traits
<https://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx>`_,
as well as nearly all of the
`Embarcadero C++ type traits
<http://docwiki.embarcadero.com/RADStudio/Rio/en/Type_Trait_Functions_(C%2B%2B11)_Index>`_.
The following type trait primitives are supported by Clang. Those traits marked
(C++) provide implementations for type traits specified by the C++ standard;
``__X(...)`` has the same semantics and constraints as the corresponding
``std::X_t<...>`` or ``std::X_v<...>`` type trait.
* ``__array_rank(type)`` (Embarcadero):
Returns the number of levels of array in the type ``type``:
``0`` if ``type`` is not an array type, and
``__array_rank(element) + 1`` if ``type`` is an array of ``element``.
* ``__array_extent(type, dim)`` (Embarcadero):
The ``dim``'th array bound in the type ``type``, or ``0`` if
``dim >= __array_rank(type)``.
* ``__has_nothrow_assign`` (GNU, Microsoft, Embarcadero):
Deprecated, use ``__is_nothrow_assignable`` instead.
* ``__has_nothrow_move_assign`` (GNU, Microsoft):
Deprecated, use ``__is_nothrow_assignable`` instead.
* ``__has_nothrow_copy`` (GNU, Microsoft):
Deprecated, use ``__is_nothrow_constructible`` instead.
* ``__has_nothrow_constructor`` (GNU, Microsoft):
Deprecated, use ``__is_nothrow_constructible`` instead.
* ``__has_trivial_assign`` (GNU, Microsoft, Embarcadero):
Deprecated, use ``__is_trivially_assignable`` instead.
* ``__has_trivial_move_assign`` (GNU, Microsoft):
Deprecated, use ``__is_trivially_assignable`` instead.
* ``__has_trivial_copy`` (GNU, Microsoft):
Deprecated, use ``__is_trivially_constructible`` instead.
* ``__has_trivial_constructor`` (GNU, Microsoft):
Deprecated, use ``__is_trivially_constructible`` instead.
* ``__has_trivial_move_constructor`` (GNU, Microsoft):
Deprecated, use ``__is_trivially_constructible`` instead.
* ``__has_trivial_destructor`` (GNU, Microsoft, Embarcadero):
Deprecated, use ``__is_trivially_destructible`` instead.
* ``__has_unique_object_representations`` (C++, GNU)
* ``__has_virtual_destructor`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_abstract`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_aggregate`` (C++, GNU, Microsoft)
* ``__is_arithmetic`` (C++, Embarcadero)
* ``__is_array`` (C++, Embarcadero)
* ``__is_assignable`` (C++, MSVC 2015)
* ``__is_base_of`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_class`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_complete_type(type)`` (Embarcadero):
Return ``true`` if ``type`` is a complete type.
Warning: this trait is dangerous because it can return different values at
different points in the same program.
* ``__is_compound`` (C++, Embarcadero)
* ``__is_const`` (C++, Embarcadero)
* ``__is_constructible`` (C++, MSVC 2013)
* ``__is_convertible`` (C++, Embarcadero)
* ``__is_convertible_to`` (Microsoft):
Synonym for ``__is_convertible``.
* ``__is_destructible`` (C++, MSVC 2013):
Only available in ``-fms-extensions`` mode.
* ``__is_empty`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_enum`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_final`` (C++, GNU, Microsoft)
* ``__is_floating_point`` (C++, Embarcadero)
* ``__is_function`` (C++, Embarcadero)
* ``__is_fundamental`` (C++, Embarcadero)
* ``__is_integral`` (C++, Embarcadero)
* ``__is_interface_class`` (Microsoft):
Returns ``false``, even for types defined with ``__interface``.
* ``__is_literal`` (Clang):
Synonym for ``__is_literal_type``.
* ``__is_literal_type`` (C++, GNU, Microsoft):
Note, the corresponding standard trait was deprecated in C++17
and removed in C++20.
* ``__is_lvalue_reference`` (C++, Embarcadero)
* ``__is_member_object_pointer`` (C++, Embarcadero)
* ``__is_member_function_pointer`` (C++, Embarcadero)
* ``__is_member_pointer`` (C++, Embarcadero)
* ``__is_nothrow_assignable`` (C++, MSVC 2013)
* ``__is_nothrow_constructible`` (C++, MSVC 2013)
* ``__is_nothrow_destructible`` (C++, MSVC 2013)
Only available in ``-fms-extensions`` mode.
* ``__is_object`` (C++, Embarcadero)
* ``__is_pod`` (C++, GNU, Microsoft, Embarcadero):
Note, the corresponding standard trait was deprecated in C++20.
* ``__is_pointer`` (C++, Embarcadero)
* ``__is_polymorphic`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_reference`` (C++, Embarcadero)
* ``__is_rvalue_reference`` (C++, Embarcadero)
* ``__is_same`` (C++, Embarcadero)
* ``__is_same_as`` (GCC): Synonym for ``__is_same``.
* ``__is_scalar`` (C++, Embarcadero)
* ``__is_sealed`` (Microsoft):
Synonym for ``__is_final``.
* ``__is_signed`` (C++, Embarcadero):
Returns false for enumeration types, and returns true for floating-point
types. Note, before Clang 10, returned true for enumeration types if the
underlying type was signed, and returned false for floating-point types.
* ``__is_standard_layout`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_trivial`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_trivially_assignable`` (C++, GNU, Microsoft)
* ``__is_trivially_constructible`` (C++, GNU, Microsoft)
* ``__is_trivially_copyable`` (C++, GNU, Microsoft)
* ``__is_trivially_destructible`` (C++, MSVC 2013)
* ``__is_union`` (C++, GNU, Microsoft, Embarcadero)
* ``__is_unsigned`` (C++, Embarcadero):
Returns false for enumeration types. Note, before Clang 13, returned true for
enumeration types if the underlying type was unsigned.
* ``__is_void`` (C++, Embarcadero)
* ``__is_volatile`` (C++, Embarcadero)
* ``__reference_binds_to_temporary(T, U)`` (Clang): Determines whether a
reference of type ``T`` bound to an expression of type ``U`` would bind to a
materialized temporary object. If ``T`` is not a reference type the result
is false. Note this trait will also return false when the initialization of
``T`` from ``U`` is ill-formed.
* ``__underlying_type`` (C++, GNU, Microsoft)
In addition, the following expression traits are supported:
* ``__is_lvalue_expr(e)`` (Embarcadero):
Returns true if ``e`` is an lvalue expression.
Deprecated, use ``__is_lvalue_reference(decltype((e)))`` instead.
* ``__is_rvalue_expr(e)`` (Embarcadero):
Returns true if ``e`` is a prvalue expression.
Deprecated, use ``!__is_reference(decltype((e)))`` instead.
There are multiple ways to detect support for a type trait ``__X`` in the
compiler, depending on the oldest version of Clang you wish to support.
* From Clang 10 onwards, ``__has_builtin(__X)`` can be used.
* From Clang 6 onwards, ``!__is_identifier(__X)`` can be used.
* From Clang 3 onwards, ``__has_feature(X)`` can be used, but only supports
the following traits:
* ``__has_nothrow_assign``
* ``__has_nothrow_copy``
* ``__has_nothrow_constructor``
* ``__has_trivial_assign``
* ``__has_trivial_copy``
* ``__has_trivial_constructor``
* ``__has_trivial_destructor``
* ``__has_virtual_destructor``
* ``__is_abstract``
* ``__is_base_of``
* ``__is_class``
* ``__is_constructible``
* ``__is_convertible_to``
* ``__is_empty``
* ``__is_enum``
* ``__is_final``
* ``__is_literal``
* ``__is_standard_layout``
* ``__is_pod``
* ``__is_polymorphic``
* ``__is_sealed``
* ``__is_trivial``
* ``__is_trivially_assignable``
* ``__is_trivially_constructible``
* ``__is_trivially_copyable``
* ``__is_union``
* ``__underlying_type``
A simplistic usage example as might be seen in standard C++ headers follows:
.. code-block:: c++
#if __has_builtin(__is_convertible_to)
template<typename From, typename To>
struct is_convertible_to {
static const bool value = __is_convertible_to(From, To);
};
#else
// Emulate type trait for compatibility with other compilers.
#endif
Blocks
======
The syntax and high level language feature description is in
:doc:`BlockLanguageSpec<BlockLanguageSpec>`. Implementation and ABI details for
the clang implementation are in :doc:`Block-ABI-Apple<Block-ABI-Apple>`.
Query for this feature with ``__has_extension(blocks)``.
ASM Goto with Output Constraints
================================
In addition to the functionality provided by `GCC's extended
assembly <https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html>`_, clang
supports output constraints with the `goto` form.
The goto form of GCC's extended assembly allows the programmer to branch to a C
label from within an inline assembly block. Clang extends this behavior by
allowing the programmer to use output constraints:
.. code-block:: c++
int foo(int x) {
int y;
asm goto("# %0 %1 %l2" : "=r"(y) : "r"(x) : : err);
return y;
err:
return -1;
}
It's important to note that outputs are valid only on the "fallthrough" branch.
Using outputs on an indirect branch may result in undefined behavior. For
example, in the function above, use of the value assigned to `y` in the `err`
block is undefined behavior.
Query for this feature with ``__has_extension(gnu_asm_goto_with_outputs)``.
Objective-C Features
====================
Related result types
--------------------
According to Cocoa conventions, Objective-C methods with certain names
("``init``", "``alloc``", etc.) always return objects that are an instance of
the receiving class's type. Such methods are said to have a "related result
type", meaning that a message send to one of these methods will have the same
static type as an instance of the receiver class. For example, given the
following classes:
.. code-block:: objc
@interface NSObject
+ (id)alloc;
- (id)init;
@end
@interface NSArray : NSObject
@end
and this common initialization pattern
.. code-block:: objc
NSArray *array = [[NSArray alloc] init];
the type of the expression ``[NSArray alloc]`` is ``NSArray*`` because
``alloc`` implicitly has a related result type. Similarly, the type of the
expression ``[[NSArray alloc] init]`` is ``NSArray*``, since ``init`` has a
related result type and its receiver is known to have the type ``NSArray *``.
If neither ``alloc`` nor ``init`` had a related result type, the expressions
would have had type ``id``, as declared in the method signature.
A method with a related result type can be declared by using the type
``instancetype`` as its result type. ``instancetype`` is a contextual keyword
that is only permitted in the result type of an Objective-C method, e.g.
.. code-block:: objc
@interface A
+ (instancetype)constructAnA;
@end
The related result type can also be inferred for some methods. To determine
whether a method has an inferred related result type, the first word in the
camel-case selector (e.g., "``init``" in "``initWithObjects``") is considered,
and the method will have a related result type if its return type is compatible
with the type of its class and if:
* the first word is "``alloc``" or "``new``", and the method is a class method,
or
* the first word is "``autorelease``", "``init``", "``retain``", or "``self``",
and the method is an instance method.
If a method with a related result type is overridden by a subclass method, the
subclass method must also return a type that is compatible with the subclass
type. For example:
.. code-block:: objc
@interface NSString : NSObject
- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
@end
Related result types only affect the type of a message send or property access
via the given method. In all other respects, a method with a related result
type is treated the same way as method that returns ``id``.
Use ``__has_feature(objc_instancetype)`` to determine whether the
``instancetype`` contextual keyword is available.
Automatic reference counting
----------------------------
Clang provides support for :doc:`automated reference counting
<AutomaticReferenceCounting>` in Objective-C, which eliminates the need
for manual ``retain``/``release``/``autorelease`` message sends. There are three
feature macros associated with automatic reference counting:
``__has_feature(objc_arc)`` indicates the availability of automated reference
counting in general, while ``__has_feature(objc_arc_weak)`` indicates that
automated reference counting also includes support for ``__weak`` pointers to
Objective-C objects. ``__has_feature(objc_arc_fields)`` indicates that C structs
are allowed to have fields that are pointers to Objective-C objects managed by
automatic reference counting.
.. _objc-weak:
Weak references
---------------
Clang supports ARC-style weak and unsafe references in Objective-C even
outside of ARC mode. Weak references must be explicitly enabled with
the ``-fobjc-weak`` option; use ``__has_feature((objc_arc_weak))``
to test whether they are enabled. Unsafe references are enabled
unconditionally. ARC-style weak and unsafe references cannot be used
when Objective-C garbage collection is enabled.
Except as noted below, the language rules for the ``__weak`` and
``__unsafe_unretained`` qualifiers (and the ``weak`` and
``unsafe_unretained`` property attributes) are just as laid out
in the :doc:`ARC specification <AutomaticReferenceCounting>`.
In particular, note that some classes do not support forming weak
references to their instances, and note that special care must be
taken when storing weak references in memory where initialization
and deinitialization are outside the responsibility of the compiler
(such as in ``malloc``-ed memory).
Loading from a ``__weak`` variable always implicitly retains the
loaded value. In non-ARC modes, this retain is normally balanced
by an implicit autorelease. This autorelease can be suppressed
by performing the load in the receiver position of a ``-retain``
message send (e.g. ``[weakReference retain]``); note that this performs
only a single retain (the retain done when primitively loading from
the weak reference).
For the most part, ``__unsafe_unretained`` in non-ARC modes is just the
default behavior of variables and therefore is not needed. However,
it does have an effect on the semantics of block captures: normally,
copying a block which captures an Objective-C object or block pointer
causes the captured pointer to be retained or copied, respectively,
but that behavior is suppressed when the captured variable is qualified
with ``__unsafe_unretained``.
Note that the ``__weak`` qualifier formerly meant the GC qualifier in
all non-ARC modes and was silently ignored outside of GC modes. It now
means the ARC-style qualifier in all non-GC modes and is no longer
allowed if not enabled by either ``-fobjc-arc`` or ``-fobjc-weak``.
It is expected that ``-fobjc-weak`` will eventually be enabled by default
in all non-GC Objective-C modes.
.. _objc-fixed-enum:
Enumerations with a fixed underlying type
-----------------------------------------
Clang provides support for C++11 enumerations with a fixed underlying type
within Objective-C. For example, one can write an enumeration type as:
.. code-block:: c++
typedef enum : unsigned char { Red, Green, Blue } Color;
This specifies that the underlying type, which is used to store the enumeration
value, is ``unsigned char``.
Use ``__has_feature(objc_fixed_enum)`` to determine whether support for fixed
underlying types is available in Objective-C.
Interoperability with C++11 lambdas
-----------------------------------
Clang provides interoperability between C++11 lambdas and blocks-based APIs, by
permitting a lambda to be implicitly converted to a block pointer with the
corresponding signature. For example, consider an API such as ``NSArray``'s
array-sorting method:
.. code-block:: objc
- (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr;
``NSComparator`` is simply a typedef for the block pointer ``NSComparisonResult
(^)(id, id)``, and parameters of this type are generally provided with block
literals as arguments. However, one can also use a C++11 lambda so long as it
provides the same signature (in this case, accepting two parameters of type
``id`` and returning an ``NSComparisonResult``):
.. code-block:: objc
NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11",
@"String 02"];
const NSStringCompareOptions comparisonOptions
= NSCaseInsensitiveSearch | NSNumericSearch |
NSWidthInsensitiveSearch | NSForcedOrderingSearch;
NSLocale *currentLocale = [NSLocale currentLocale];
NSArray *sorted
= [array sortedArrayUsingComparator:[=](id s1, id s2) -> NSComparisonResult {
NSRange string1Range = NSMakeRange(0, [s1 length]);
return [s1 compare:s2 options:comparisonOptions
range:string1Range locale:currentLocale];
}];
NSLog(@"sorted: %@", sorted);
This code relies on an implicit conversion from the type of the lambda
expression (an unnamed, local class type called the *closure type*) to the
corresponding block pointer type. The conversion itself is expressed by a
conversion operator in that closure type that produces a block pointer with the
same signature as the lambda itself, e.g.,
.. code-block:: objc
operator NSComparisonResult (^)(id, id)() const;
This conversion function returns a new block that simply forwards the two
parameters to the lambda object (which it captures by copy), then returns the
result. The returned block is first copied (with ``Block_copy``) and then
autoreleased. As an optimization, if a lambda expression is immediately
converted to a block pointer (as in the first example, above), then the block
is not copied and autoreleased: rather, it is given the same lifetime as a
block literal written at that point in the program, which avoids the overhead
of copying a block to the heap in the common case.
The conversion from a lambda to a block pointer is only available in
Objective-C++, and not in C++ with blocks, due to its use of Objective-C memory
management (autorelease).
Object Literals and Subscripting
--------------------------------
Clang provides support for :doc:`Object Literals and Subscripting
<ObjectiveCLiterals>` in Objective-C, which simplifies common Objective-C
programming patterns, makes programs more concise, and improves the safety of
container creation. There are several feature macros associated with object
literals and subscripting: ``__has_feature(objc_array_literals)`` tests the
availability of array literals; ``__has_feature(objc_dictionary_literals)``
tests the availability of dictionary literals;
``__has_feature(objc_subscripting)`` tests the availability of object
subscripting.
Objective-C Autosynthesis of Properties
---------------------------------------
Clang provides support for autosynthesis of declared properties. Using this
feature, clang provides default synthesis of those properties not declared
@dynamic and not having user provided backing getter and setter methods.
``__has_feature(objc_default_synthesize_properties)`` checks for availability
of this feature in version of clang being used.
.. _langext-objc-retain-release:
Objective-C retaining behavior attributes
-----------------------------------------
In Objective-C, functions and methods are generally assumed to follow the
`Cocoa Memory Management
<https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html>`_
conventions for ownership of object arguments and
return values. However, there are exceptions, and so Clang provides attributes
to allow these exceptions to be documented. This are used by ARC and the
`static analyzer <https://clang-analyzer.llvm.org>`_ Some exceptions may be
better described using the ``objc_method_family`` attribute instead.
**Usage**: The ``ns_returns_retained``, ``ns_returns_not_retained``,
``ns_returns_autoreleased``, ``cf_returns_retained``, and
``cf_returns_not_retained`` attributes can be placed on methods and functions
that return Objective-C or CoreFoundation objects. They are commonly placed at
the end of a function prototype or method declaration:
.. code-block:: objc
id foo() __attribute__((ns_returns_retained));
- (NSString *)bar:(int)x __attribute__((ns_returns_retained));
The ``*_returns_retained`` attributes specify that the returned object has a +1
retain count. The ``*_returns_not_retained`` attributes specify that the return
object has a +0 retain count, even if the normal convention for its selector
would be +1. ``ns_returns_autoreleased`` specifies that the returned object is
+0, but is guaranteed to live at least as long as the next flush of an
autorelease pool.
**Usage**: The ``ns_consumed`` and ``cf_consumed`` attributes can be placed on
an parameter declaration; they specify that the argument is expected to have a
+1 retain count, which will be balanced in some way by the function or method.
The ``ns_consumes_self`` attribute can only be placed on an Objective-C
method; it specifies that the method expects its ``self`` parameter to have a
+1 retain count, which it will balance in some way.
.. code-block:: objc
void foo(__attribute__((ns_consumed)) NSString *string);
- (void) bar __attribute__((ns_consumes_self));
- (void) baz:(id) __attribute__((ns_consumed)) x;
Further examples of these attributes are available in the static analyzer's `list of annotations for analysis
<https://clang-analyzer.llvm.org/annotations.html#cocoa_mem>`_.
Query for these features with ``__has_attribute(ns_consumed)``,
``__has_attribute(ns_returns_retained)``, etc.
Objective-C @available
----------------------
It is possible to use the newest SDK but still build a program that can run on
older versions of macOS and iOS by passing ``-mmacosx-version-min=`` /
``-miphoneos-version-min=``.
Before LLVM 5.0, when calling a function that exists only in the OS that's
newer than the target OS (as determined by the minimum deployment version),
programmers had to carefully check if the function exists at runtime, using
null checks for weakly-linked C functions, ``+class`` for Objective-C classes,
and ``-respondsToSelector:`` or ``+instancesRespondToSelector:`` for
Objective-C methods. If such a check was missed, the program would compile
fine, run fine on newer systems, but crash on older systems.
As of LLVM 5.0, ``-Wunguarded-availability`` uses the `availability attributes
<https://clang.llvm.org/docs/AttributeReference.html#availability>`_ together
with the new ``@available()`` keyword to assist with this issue.
When a method that's introduced in the OS newer than the target OS is called, a
-Wunguarded-availability warning is emitted if that call is not guarded:
.. code-block:: objc
void my_fun(NSSomeClass* var) {
// If fancyNewMethod was added in e.g. macOS 10.12, but the code is
// built with -mmacosx-version-min=10.11, then this unconditional call
// will emit a -Wunguarded-availability warning:
[var fancyNewMethod];
}
To fix the warning and to avoid the crash on macOS 10.11, wrap it in
``if(@available())``:
.. code-block:: objc
void my_fun(NSSomeClass* var) {
if (@available(macOS 10.12, *)) {
[var fancyNewMethod];
} else {
// Put fallback behavior for old macOS versions (and for non-mac
// platforms) here.
}
}
The ``*`` is required and means that platforms not explicitly listed will take
the true branch, and the compiler will emit ``-Wunguarded-availability``
warnings for unlisted platforms based on those platform's deployment target.
More than one platform can be listed in ``@available()``:
.. code-block:: objc
void my_fun(NSSomeClass* var) {
if (@available(macOS 10.12, iOS 10, *)) {
[var fancyNewMethod];
}
}
If the caller of ``my_fun()`` already checks that ``my_fun()`` is only called
on 10.12, then add an `availability attribute
<https://clang.llvm.org/docs/AttributeReference.html#availability>`_ to it,
which will also suppress the warning and require that calls to my_fun() are
checked:
.. code-block:: objc
API_AVAILABLE(macos(10.12)) void my_fun(NSSomeClass* var) {
[var fancyNewMethod]; // Now ok.
}
``@available()`` is only available in Objective-C code. To use the feature
in C and C++ code, use the ``__builtin_available()`` spelling instead.
If existing code uses null checks or ``-respondsToSelector:``, it should
be changed to use ``@available()`` (or ``__builtin_available``) instead.
``-Wunguarded-availability`` is disabled by default, but
``-Wunguarded-availability-new``, which only emits this warning for APIs
that have been introduced in macOS >= 10.13, iOS >= 11, watchOS >= 4 and
tvOS >= 11, is enabled by default.
.. _langext-overloading:
Objective-C++ ABI: protocol-qualifier mangling of parameters
------------------------------------------------------------
Starting with LLVM 3.4, Clang produces a new mangling for parameters whose
type is a qualified-``id`` (e.g., ``id<Foo>``). This mangling allows such
parameters to be differentiated from those with the regular unqualified ``id``
type.
This was a non-backward compatible mangling change to the ABI. This change
allows proper overloading, and also prevents mangling conflicts with template
parameters of protocol-qualified type.
Query the presence of this new mangling with
``__has_feature(objc_protocol_qualifier_mangling)``.
Initializer lists for complex numbers in C
==========================================
clang supports an extension which allows the following in C:
.. code-block:: c++
#include <math.h>
#include <complex.h>
complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
This construct is useful because there is no way to separately initialize the
real and imaginary parts of a complex variable in standard C, given that clang
does not support ``_Imaginary``. (Clang also supports the ``__real__`` and
``__imag__`` extensions from gcc, which help in some cases, but are not usable
in static initializers.)
Note that this extension does not allow eliding the braces; the meaning of the
following two lines is different:
.. code-block:: c++
complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
This extension also works in C++ mode, as far as that goes, but does not apply
to the C++ ``std::complex``. (In C++11, list initialization allows the same
syntax to be used with ``std::complex`` with the same meaning.)
For GCC compatibility, ``__builtin_complex(re, im)`` can also be used to
construct a complex number from the given real and imaginary components.
OpenCL Features
===============
Clang supports internal OpenCL extensions documented below.
``__cl_clang_bitfields``
--------------------------------
With this extension it is possible to enable bitfields in structs
or unions using the OpenCL extension pragma mechanism detailed in
`the OpenCL Extension Specification, section 1.2
<https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_Ext.html#extensions-overview>`_.
Use of bitfields in OpenCL kernels can result in reduced portability as struct
layout is not guaranteed to be consistent when compiled by different compilers.
If structs with bitfields are used as kernel function parameters, it can result
in incorrect functionality when the layout is different between the host and
device code.
**Example of Use**:
.. code-block:: c++
#pragma OPENCL EXTENSION __cl_clang_bitfields : enable
struct with_bitfield {
unsigned int i : 5; // compiled - no diagnostic generated
};
#pragma OPENCL EXTENSION __cl_clang_bitfields : disable
struct without_bitfield {
unsigned int i : 5; // error - bitfields are not supported
};
``__cl_clang_function_pointers``
--------------------------------
With this extension it is possible to enable various language features that
are relying on function pointers using regular OpenCL extension pragma
mechanism detailed in `the OpenCL Extension Specification,
section 1.2
<https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_Ext.html#extensions-overview>`_.
In C++ for OpenCL this also enables:
- Use of member function pointers;
- Unrestricted use of references to functions;
- Virtual member functions.
Such functionality is not conformant and does not guarantee to compile
correctly in any circumstances. It can be used if:
- the kernel source does not contain call expressions to (member-) function
pointers, or virtual functions. For example this extension can be used in
metaprogramming algorithms to be able to specify/detect types generically.
- the generated kernel binary does not contain indirect calls because they
are eliminated using compiler optimizations e.g. devirtualization.
- the selected target supports the function pointer like functionality e.g.
most CPU targets.
**Example of Use**:
.. code-block:: c++
#pragma OPENCL EXTENSION __cl_clang_function_pointers : enable
void foo()
{
void (*fp)(); // compiled - no diagnostic generated
}
#pragma OPENCL EXTENSION __cl_clang_function_pointers : disable
void bar()
{
void (*fp)(); // error - pointers to function are not allowed
}
``__cl_clang_variadic_functions``
---------------------------------
With this extension it is possible to enable variadic arguments in functions
using regular OpenCL extension pragma mechanism detailed in `the OpenCL
Extension Specification, section 1.2
<https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_Ext.html#extensions-overview>`_.
This is not conformant behavior and it can only be used portably when the
functions with variadic prototypes do not get generated in binary e.g. the
variadic prototype is used to specify a function type with any number of
arguments in metaprogramming algorithms in C++ for OpenCL.
This extensions can also be used when the kernel code is intended for targets
supporting the variadic arguments e.g. majority of CPU targets.
**Example of Use**:
.. code-block:: c++
#pragma OPENCL EXTENSION __cl_clang_variadic_functions : enable
void foo(int a, ...); // compiled - no diagnostic generated
#pragma OPENCL EXTENSION __cl_clang_variadic_functions : disable
void bar(int a, ...); // error - variadic prototype is not allowed
``__cl_clang_non_portable_kernel_param_types``
----------------------------------------------
With this extension it is possible to enable the use of some restricted types
in kernel parameters specified in `C++ for OpenCL v1.0 s2.4
<https://www.khronos.org/opencl/assets/CXX_for_OpenCL.html#kernel_function>`_.
The restrictions can be relaxed using regular OpenCL extension pragma mechanism
detailed in `the OpenCL Extension Specification, section 1.2
<https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_Ext.html#extensions-overview>`_.
This is not a conformant behavior and it can only be used when the
kernel arguments are not accessed on the host side or the data layout/size
between the host and device is known to be compatible.
**Example of Use**:
.. code-block:: c++
// Plain Old Data type.
struct Pod {
int a;
int b;
};
// Not POD type because of the constructor.
// Standard layout type because there is only one access control.
struct OnlySL {
int a;
int b;
NotPod() : a(0), b(0) {}
};
// Not standard layout type because of two different access controls.
struct NotSL {
int a;
private:
int b;
}
kernel void kernel_main(
Pod a,
#pragma OPENCL EXTENSION __cl_clang_non_portable_kernel_param_types : enable
OnlySL b,
global NotSL *c,
#pragma OPENCL EXTENSION __cl_clang_non_portable_kernel_param_types : disable
global OnlySL *d,
);
Remove address space builtin function
-------------------------------------
``__remove_address_space`` allows to derive types in C++ for OpenCL
that have address space qualifiers removed. This utility only affects
address space qualifiers, therefore, other type qualifiers such as
``const`` or ``volatile`` remain unchanged.
**Example of Use**:
.. code-block:: c++
template<typename T>
void foo(T *par){
T var1; // error - local function variable with global address space
__private T var2; // error - conflicting address space qualifiers
__private __remove_address_space<T> var3; // var3 is __private int
}
void bar(){
__global int* ptr;
foo(ptr);
}
Legacy 1.x atomics with generic address space
---------------------------------------------
Clang allows use of atomic functions from the OpenCL 1.x standards
with the generic address space pointer in C++ for OpenCL mode.
This is a non-portable feature and might not be supported by all
targets.
**Example of Use**:
.. code-block:: c++
void foo(__generic volatile unsigned int* a) {
atomic_add(a, 1);
}
Builtin Functions
=================
Clang supports a number of builtin library functions with the same syntax as
GCC, including things like ``__builtin_nan``, ``__builtin_constant_p``,
``__builtin_choose_expr``, ``__builtin_types_compatible_p``,
``__builtin_assume_aligned``, ``__sync_fetch_and_add``, etc. In addition to
the GCC builtins, Clang supports a number of builtins that GCC does not, which
are listed here.
Please note that Clang does not and will not support all of the GCC builtins
for vector operations. Instead of using builtins, you should use the functions
defined in target-specific header files like ``<xmmintrin.h>``, which define
portable wrappers for these. Many of the Clang versions of these functions are
implemented directly in terms of :ref:`extended vector support
<langext-vectors>` instead of builtins, in order to reduce the number of
builtins that we need to implement.
.. _langext-__builtin_assume:
``__builtin_assume``
------------------------------
``__builtin_assume`` is used to provide the optimizer with a boolean
invariant that is defined to be true.
**Syntax**:
.. code-block:: c++
__builtin_assume(bool)
**Example of Use**:
.. code-block:: c++
int foo(int x) {
__builtin_assume(x != 0);
// The optimizer may short-circuit this check using the invariant.
if (x == 0)
return do_something();
return do_something_else();
}
**Description**:
The boolean argument to this function is defined to be true. The optimizer may
analyze the form of the expression provided as the argument and deduce from
that information used to optimize the program. If the condition is violated
during execution, the behavior is undefined. The argument itself is never
evaluated, so any side effects of the expression will be discarded.
Query for this feature with ``__has_builtin(__builtin_assume)``.
``__builtin_readcyclecounter``
------------------------------
``__builtin_readcyclecounter`` is used to access the cycle counter register (or
a similar low-latency, high-accuracy clock) on those targets that support it.
**Syntax**:
.. code-block:: c++
__builtin_readcyclecounter()
**Example of Use**:
.. code-block:: c++
unsigned long long t0 = __builtin_readcyclecounter();
do_something();
unsigned long long t1 = __builtin_readcyclecounter();
unsigned long long cycles_to_do_something = t1 - t0; // assuming no overflow
**Description**:
The ``__builtin_readcyclecounter()`` builtin returns the cycle counter value,
which may be either global or process/thread-specific depending on the target.
As the backing counters often overflow quickly (on the order of seconds) this
should only be used for timing small intervals. When not supported by the
target, the return value is always zero. This builtin takes no arguments and
produces an unsigned long long result.
Query for this feature with ``__has_builtin(__builtin_readcyclecounter)``. Note
that even if present, its use may depend on run-time privilege or other OS
controlled state.
``__builtin_dump_struct``
-------------------------
**Syntax**:
.. code-block:: c++
__builtin_dump_struct(&some_struct, &some_printf_func);
**Examples**:
.. code-block:: c++
struct S {
int x, y;
float f;
struct T {
int i;
} t;
};
void func(struct S *s) {
__builtin_dump_struct(s, &printf);
}
Example output:
.. code-block:: none
struct S {
int i : 100
int j : 42
float f : 3.14159
struct T t : struct T {
int i : 1997
}
}
**Description**:
The '``__builtin_dump_struct``' function is used to print the fields of a simple
structure and their values for debugging purposes. The builtin accepts a pointer
to a structure to dump the fields of, and a pointer to a formatted output
function whose signature must be: ``int (*)(const char *, ...)`` and must
support the format specifiers used by ``printf()``.
.. _langext-__builtin_shufflevector:
``__builtin_shufflevector``
---------------------------
``__builtin_shufflevector`` is used to express generic vector
permutation/shuffle/swizzle operations. This builtin is also very important
for the implementation of various target-specific header files like
``<xmmintrin.h>``.
**Syntax**:
.. code-block:: c++
__builtin_shufflevector(vec1, vec2, index1, index2, ...)
**Examples**:
.. code-block:: c++
// identity operation - return 4-element vector v1.
__builtin_shufflevector(v1, v1, 0, 1, 2, 3)
// "Splat" element 0 of V1 into a 4-element result.
__builtin_shufflevector(V1, V1, 0, 0, 0, 0)
// Reverse 4-element vector V1.
__builtin_shufflevector(V1, V1, 3, 2, 1, 0)
// Concatenate every other element of 4-element vectors V1 and V2.
__builtin_shufflevector(V1, V2, 0, 2, 4, 6)
// Concatenate every other element of 8-element vectors V1 and V2.
__builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
// Shuffle v1 with some elements being undefined
__builtin_shufflevector(v1, v1, 3, -1, 1, -1)
**Description**:
The first two arguments to ``__builtin_shufflevector`` are vectors that have
the same element type. The remaining arguments are a list of integers that
specify the elements indices of the first two vectors that should be extracted
and returned in a new vector. These element indices are numbered sequentially
starting with the first vector, continuing into the second vector. Thus, if
``vec1`` is a 4-element vector, index 5 would refer to the second element of
``vec2``. An index of -1 can be used to indicate that the corresponding element
in the returned vector is a don't care and can be optimized by the backend.
The result of ``__builtin_shufflevector`` is a vector with the same element
type as ``vec1``/``vec2`` but that has an element count equal to the number of
indices specified.
Query for this feature with ``__has_builtin(__builtin_shufflevector)``.
.. _langext-__builtin_convertvector:
``__builtin_convertvector``
---------------------------
``__builtin_convertvector`` is used to express generic vector
type-conversion operations. The input vector and the output vector
type must have the same number of elements.
**Syntax**:
.. code-block:: c++
__builtin_convertvector(src_vec, dst_vec_type)
**Examples**:
.. code-block:: c++
typedef double vector4double __attribute__((__vector_size__(32)));
typedef float vector4float __attribute__((__vector_size__(16)));
typedef short vector4short __attribute__((__vector_size__(8)));
vector4float vf; vector4short vs;
// convert from a vector of 4 floats to a vector of 4 doubles.
__builtin_convertvector(vf, vector4double)
// equivalent to:
(vector4double) { (double) vf[0], (double) vf[1], (double) vf[2], (double) vf[3] }
// convert from a vector of 4 shorts to a vector of 4 floats.
__builtin_convertvector(vs, vector4float)
// equivalent to:
(vector4float) { (float) vs[0], (float) vs[1], (float) vs[2], (float) vs[3] }
**Description**:
The first argument to ``__builtin_convertvector`` is a vector, and the second
argument is a vector type with the same number of elements as the first
argument.
The result of ``__builtin_convertvector`` is a vector with the same element
type as the second argument, with a value defined in terms of the action of a
C-style cast applied to each element of the first argument.
Query for this feature with ``__has_builtin(__builtin_convertvector)``.
``__builtin_bitreverse``
------------------------
* ``__builtin_bitreverse8``
* ``__builtin_bitreverse16``
* ``__builtin_bitreverse32``
* ``__builtin_bitreverse64``
**Syntax**:
.. code-block:: c++
__builtin_bitreverse32(x)
**Examples**:
.. code-block:: c++
uint8_t rev_x = __builtin_bitreverse8(x);
uint16_t rev_x = __builtin_bitreverse16(x);
uint32_t rev_y = __builtin_bitreverse32(y);
uint64_t rev_z = __builtin_bitreverse64(z);
**Description**:
The '``__builtin_bitreverse``' family of builtins is used to reverse
the bitpattern of an integer value; for example ``0b10110110`` becomes
``0b01101101``. These builtins can be used within constant expressions.
``__builtin_rotateleft``
------------------------
* ``__builtin_rotateleft8``
* ``__builtin_rotateleft16``
* ``__builtin_rotateleft32``
* ``__builtin_rotateleft64``
**Syntax**:
.. code-block:: c++
__builtin_rotateleft32(x, y)
**Examples**:
.. code-block:: c++
uint8_t rot_x = __builtin_rotateleft8(x, y);
uint16_t rot_x = __builtin_rotateleft16(x, y);
uint32_t rot_x = __builtin_rotateleft32(x, y);
uint64_t rot_x = __builtin_rotateleft64(x, y);
**Description**:
The '``__builtin_rotateleft``' family of builtins is used to rotate
the bits in the first argument by the amount in the second argument.
For example, ``0b10000110`` rotated left by 11 becomes ``0b00110100``.
The shift value is treated as an unsigned amount modulo the size of
the arguments. Both arguments and the result have the bitwidth specified
by the name of the builtin. These builtins can be used within constant
expressions.
``__builtin_rotateright``
-------------------------
* ``__builtin_rotateright8``
* ``__builtin_rotateright16``
* ``__builtin_rotateright32``
* ``__builtin_rotateright64``
**Syntax**:
.. code-block:: c++
__builtin_rotateright32(x, y)
**Examples**:
.. code-block:: c++
uint8_t rot_x = __builtin_rotateright8(x, y);
uint16_t rot_x = __builtin_rotateright16(x, y);
uint32_t rot_x = __builtin_rotateright32(x, y);
uint64_t rot_x = __builtin_rotateright64(x, y);
**Description**:
The '``__builtin_rotateright``' family of builtins is used to rotate
the bits in the first argument by the amount in the second argument.
For example, ``0b10000110`` rotated right by 3 becomes ``0b11010000``.
The shift value is treated as an unsigned amount modulo the size of
the arguments. Both arguments and the result have the bitwidth specified
by the name of the builtin. These builtins can be used within constant
expressions.
``__builtin_unreachable``
-------------------------
``__builtin_unreachable`` is used to indicate that a specific point in the
program cannot be reached, even if the compiler might otherwise think it can.
This is useful to improve optimization and eliminates certain warnings. For
example, without the ``__builtin_unreachable`` in the example below, the
compiler assumes that the inline asm can fall through and prints a "function
declared '``noreturn``' should not return" warning.
**Syntax**:
.. code-block:: c++
__builtin_unreachable()
**Example of use**:
.. code-block:: c++
void myabort(void) __attribute__((noreturn));
void myabort(void) {
asm("int3");
__builtin_unreachable();
}
**Description**:
The ``__builtin_unreachable()`` builtin has completely undefined behavior.
Since it has undefined behavior, it is a statement that it is never reached and
the optimizer can take advantage of this to produce better code. This builtin
takes no arguments and produces a void result.
Query for this feature with ``__has_builtin(__builtin_unreachable)``.
``__builtin_unpredictable``
---------------------------
``__builtin_unpredictable`` is used to indicate that a branch condition is
unpredictable by hardware mechanisms such as branch prediction logic.
**Syntax**:
.. code-block:: c++
__builtin_unpredictable(long long)
**Example of use**:
.. code-block:: c++
if (__builtin_unpredictable(x > 0)) {
foo();
}
**Description**:
The ``__builtin_unpredictable()`` builtin is expected to be used with control
flow conditions such as in ``if`` and ``switch`` statements.
Query for this feature with ``__has_builtin(__builtin_unpredictable)``.
``__sync_swap``
---------------
``__sync_swap`` is used to atomically swap integers or pointers in memory.
**Syntax**:
.. code-block:: c++
type __sync_swap(type *ptr, type value, ...)
**Example of Use**:
.. code-block:: c++
int old_value = __sync_swap(&value, new_value);
**Description**:
The ``__sync_swap()`` builtin extends the existing ``__sync_*()`` family of
atomic intrinsics to allow code to atomically swap the current value with the
new value. More importantly, it helps developers write more efficient and
correct code by avoiding expensive loops around
``__sync_bool_compare_and_swap()`` or relying on the platform specific
implementation details of ``__sync_lock_test_and_set()``. The
``__sync_swap()`` builtin is a full barrier.
``__builtin_addressof``
-----------------------
``__builtin_addressof`` performs the functionality of the built-in ``&``
operator, ignoring any ``operator&`` overload. This is useful in constant
expressions in C++11, where there is no other way to take the address of an
object that overloads ``operator&``.
**Example of use**:
.. code-block:: c++
template<typename T> constexpr T *addressof(T &value) {
return __builtin_addressof(value);
}
``__builtin_operator_new`` and ``__builtin_operator_delete``
------------------------------------------------------------
A call to ``__builtin_operator_new(args)`` is exactly the same as a call to
``::operator new(args)``, except that it allows certain optimizations
that the C++ standard does not permit for a direct function call to
``::operator new`` (in particular, removing ``new`` / ``delete`` pairs and
merging allocations), and that the call is required to resolve to a
`replaceable global allocation function
<https://en.cppreference.com/w/cpp/memory/new/operator_new>`_.
Likewise, ``__builtin_operator_delete`` is exactly the same as a call to
``::operator delete(args)``, except that it permits optimizations
and that the call is required to resolve to a
`replaceable global deallocation function
<https://en.cppreference.com/w/cpp/memory/new/operator_delete>`_.
These builtins are intended for use in the implementation of ``std::allocator``
and other similar allocation libraries, and are only available in C++.
Query for this feature with ``__has_builtin(__builtin_operator_new)`` or
``__has_builtin(__builtin_operator_delete)``:
* If the value is at least ``201802L``, the builtins behave as described above.
* If the value is non-zero, the builtins may not support calling arbitrary
replaceable global (de)allocation functions, but do support calling at least
``::operator new(size_t)`` and ``::operator delete(void*)``.
``__builtin_preserve_access_index``
-----------------------------------
``__builtin_preserve_access_index`` specifies a code section where
array subscript access and structure/union member access are relocatable
under bpf compile-once run-everywhere framework. Debuginfo (typically
with ``-g``) is needed, otherwise, the compiler will exit with an error.
The return type for the intrinsic is the same as the type of the
argument.
**Syntax**:
.. code-block:: c
type __builtin_preserve_access_index(type arg)
**Example of Use**:
.. code-block:: c
struct t {
int i;
int j;
union {
int a;
int b;
} c[4];
};
struct t *v = ...;
int *pb =__builtin_preserve_access_index(&v->c[3].b);
__builtin_preserve_access_index(v->j);
``__builtin_sycl_unique_stable_name``
-------------------------------------
``__builtin_sycl_unique_stable_name()`` is a builtin that takes a type and
produces a string literal containing a unique name for the type that is stable
across split compilations, mainly to support SYCL/Data Parallel C++ language.
In cases where the split compilation needs to share a unique token for a type
across the boundary (such as in an offloading situation), this name can be used
for lookup purposes, such as in the SYCL Integration Header.
The value of this builtin is computed entirely at compile time, so it can be
used in constant expressions. This value encodes lambda functions based on a
stable numbering order in which they appear in their local declaration contexts.
Once this builtin is evaluated in a constexpr context, it is erroneous to use
it in an instantiation which changes its value.
In order to produce the unique name, the current implementation of the bultin
uses Itanium mangling even if the host compilation uses a different name
mangling scheme at runtime. The mangler marks all the lambdas required to name
the SYCL kernel and emits a stable local ordering of the respective lambdas,
starting from ``10000``. The initial value of ``10000`` serves as an obvious
differentiator from ordinary lambda mangling numbers but does not serve any
other purpose and may change in the future. The resulting pattern is
demanglable. When non-lambda types are passed to the builtin, the mangler emits
their usual pattern without any special treatment.
**Syntax**:
.. code-block:: c
// Computes a unique stable name for the given type.
constexpr const char * __builtin_sycl_unique_stable_name( type-id );
Multiprecision Arithmetic Builtins
----------------------------------
Clang provides a set of builtins which expose multiprecision arithmetic in a
manner amenable to C. They all have the following form:
.. code-block:: c
unsigned x = ..., y = ..., carryin = ..., carryout;
unsigned sum = __builtin_addc(x, y, carryin, &carryout);
Thus one can form a multiprecision addition chain in the following manner:
.. code-block:: c
unsigned *x, *y, *z, carryin=0, carryout;
z[0] = __builtin_addc(x[0], y[0], carryin, &carryout);
carryin = carryout;
z[1] = __builtin_addc(x[1], y[1], carryin, &carryout);
carryin = carryout;
z[2] = __builtin_addc(x[2], y[2], carryin, &carryout);
carryin = carryout;
z[3] = __builtin_addc(x[3], y[3], carryin, &carryout);
The complete list of builtins are:
.. code-block:: c
unsigned char __builtin_addcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout);
unsigned short __builtin_addcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout);
unsigned __builtin_addc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout);
unsigned long __builtin_addcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout);
unsigned long long __builtin_addcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout);
unsigned char __builtin_subcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout);
unsigned short __builtin_subcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout);
unsigned __builtin_subc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout);
unsigned long __builtin_subcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout);
unsigned long long __builtin_subcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout);
Checked Arithmetic Builtins
---------------------------
Clang provides a set of builtins that implement checked arithmetic for security
critical applications in a manner that is fast and easily expressible in C. As
an example of their usage:
.. code-block:: c
errorcode_t security_critical_application(...) {
unsigned x, y, result;
...
if (__builtin_mul_overflow(x, y, &result))
return kErrorCodeHackers;
...
use_multiply(result);
...
}
Clang provides the following checked arithmetic builtins:
.. code-block:: c
bool __builtin_add_overflow (type1 x, type2 y, type3 *sum);
bool __builtin_sub_overflow (type1 x, type2 y, type3 *diff);
bool __builtin_mul_overflow (type1 x, type2 y, type3 *prod);
bool __builtin_uadd_overflow (unsigned x, unsigned y, unsigned *sum);
bool __builtin_uaddl_overflow (unsigned long x, unsigned long y, unsigned long *sum);
bool __builtin_uaddll_overflow(unsigned long long x, unsigned long long y, unsigned long long *sum);
bool __builtin_usub_overflow (unsigned x, unsigned y, unsigned *diff);
bool __builtin_usubl_overflow (unsigned long x, unsigned long y, unsigned long *diff);
bool __builtin_usubll_overflow(unsigned long long x, unsigned long long y, unsigned long long *diff);
bool __builtin_umul_overflow (unsigned x, unsigned y, unsigned *prod);
bool __builtin_umull_overflow (unsigned long x, unsigned long y, unsigned long *prod);
bool __builtin_umulll_overflow(unsigned long long x, unsigned long long y, unsigned long long *prod);
bool __builtin_sadd_overflow (int x, int y, int *sum);
bool __builtin_saddl_overflow (long x, long y, long *sum);
bool __builtin_saddll_overflow(long long x, long long y, long long *sum);
bool __builtin_ssub_overflow (int x, int y, int *diff);
bool __builtin_ssubl_overflow (long x, long y, long *diff);
bool __builtin_ssubll_overflow(long long x, long long y, long long *diff);
bool __builtin_smul_overflow (int x, int y, int *prod);
bool __builtin_smull_overflow (long x, long y, long *prod);
bool __builtin_smulll_overflow(long long x, long long y, long long *prod);
Each builtin performs the specified mathematical operation on the
first two arguments and stores the result in the third argument. If
possible, the result will be equal to mathematically-correct result
and the builtin will return 0. Otherwise, the builtin will return
1 and the result will be equal to the unique value that is equivalent
to the mathematically-correct result modulo two raised to the *k*
power, where *k* is the number of bits in the result type. The
behavior of these builtins is well-defined for all argument values.
The first three builtins work generically for operands of any integer type,
including boolean types. The operands need not have the same type as each
other, or as the result. The other builtins may implicitly promote or
convert their operands before performing the operation.
Query for this feature with ``__has_builtin(__builtin_add_overflow)``, etc.
Floating point builtins
---------------------------------------
``__builtin_canonicalize``
--------------------------
.. code-block:: c
double __builtin_canonicalize(double);
float __builtin_canonicalizef(float);
long double__builtin_canonicalizel(long double);
Returns the platform specific canonical encoding of a floating point
number. This canonicalization is useful for implementing certain
numeric primitives such as frexp. See `LLVM canonicalize intrinsic
<https://llvm.org/docs/LangRef.html#llvm-canonicalize-intrinsic>`_ for
more information on the semantics.
String builtins
---------------
Clang provides constant expression evaluation support for builtins forms of
the following functions from the C standard library headers
``<string.h>`` and ``<wchar.h>``:
* ``memchr``
* ``memcmp`` (and its deprecated BSD / POSIX alias ``bcmp``)
* ``strchr``
* ``strcmp``
* ``strlen``
* ``strncmp``
* ``wcschr``
* ``wcscmp``
* ``wcslen``
* ``wcsncmp``
* ``wmemchr``
* ``wmemcmp``
In each case, the builtin form has the name of the C library function prefixed
by ``__builtin_``. Example:
.. code-block:: c
void *p = __builtin_memchr("foobar", 'b', 5);
In addition to the above, one further builtin is provided:
.. code-block:: c
char *__builtin_char_memchr(const char *haystack, int needle, size_t size);
``__builtin_char_memchr(a, b, c)`` is identical to
``(char*)__builtin_memchr(a, b, c)`` except that its use is permitted within
constant expressions in C++11 onwards (where a cast from ``void*`` to ``char*``
is disallowed in general).
Constant evaluation support for the ``__builtin_mem*`` functions is provided
only for arrays of ``char``, ``signed char``, ``unsigned char``, or ``char8_t``,
despite these functions accepting an argument of type ``const void*``.
Support for constant expression evaluation for the above builtins can be detected
with ``__has_feature(cxx_constexpr_string_builtins)``.
Memory builtins
---------------
Clang provides constant expression evaluation support for builtin forms of the
following functions from the C standard library headers
``<string.h>`` and ``<wchar.h>``:
* ``memcpy``
* ``memmove``
* ``wmemcpy``
* ``wmemmove``
In each case, the builtin form has the name of the C library function prefixed
by ``__builtin_``.
Constant evaluation support is only provided when the source and destination
are pointers to arrays with the same trivially copyable element type, and the
given size is an exact multiple of the element size that is no greater than
the number of elements accessible through the source and destination operands.
Guaranteed inlined copy
^^^^^^^^^^^^^^^^^^^^^^^
.. code-block:: c
void __builtin_memcpy_inline(void *dst, const void *src, size_t size);
``__builtin_memcpy_inline`` has been designed as a building block for efficient
``memcpy`` implementations. It is identical to ``__builtin_memcpy`` but also
guarantees not to call any external functions. See LLVM IR `llvm.memcpy.inline
<https://llvm.org/docs/LangRef.html#llvm-memcpy-inline-intrinsic>`_ intrinsic
for more information.
This is useful to implement a custom version of ``memcpy``, implement a
``libc`` memcpy or work around the absence of a ``libc``.
Note that the `size` argument must be a compile time constant.
Note that this intrinsic cannot yet be called in a ``constexpr`` context.
Atomic Min/Max builtins with memory ordering
--------------------------------------------
There are two atomic builtins with min/max in-memory comparison and swap.
The syntax and semantics are similar to GCC-compatible __atomic_* builtins.
* ``__atomic_fetch_min``
* ``__atomic_fetch_max``
The builtins work with signed and unsigned integers and require to specify memory ordering.
The return value is the original value that was stored in memory before comparison.
Example:
.. code-block:: c
unsigned int val = __atomic_fetch_min(unsigned int *pi, unsigned int ui, __ATOMIC_RELAXED);
The third argument is one of the memory ordering specifiers ``__ATOMIC_RELAXED``,
``__ATOMIC_CONSUME``, ``__ATOMIC_ACQUIRE``, ``__ATOMIC_RELEASE``,
``__ATOMIC_ACQ_REL``, or ``__ATOMIC_SEQ_CST`` following C++11 memory model semantics.
In terms or aquire-release ordering barriers these two operations are always
considered as operations with *load-store* semantics, even when the original value
is not actually modified after comparison.
.. _langext-__c11_atomic:
__c11_atomic builtins
---------------------
Clang provides a set of builtins which are intended to be used to implement
C11's ``<stdatomic.h>`` header. These builtins provide the semantics of the
``_explicit`` form of the corresponding C11 operation, and are named with a
``__c11_`` prefix. The supported operations, and the differences from
the corresponding C11 operations, are:
* ``__c11_atomic_init``
* ``__c11_atomic_thread_fence``
* ``__c11_atomic_signal_fence``
* ``__c11_atomic_is_lock_free`` (The argument is the size of the
``_Atomic(...)`` object, instead of its address)
* ``__c11_atomic_store``
* ``__c11_atomic_load``
* ``__c11_atomic_exchange``
* ``__c11_atomic_compare_exchange_strong``
* ``__c11_atomic_compare_exchange_weak``
* ``__c11_atomic_fetch_add``
* ``__c11_atomic_fetch_sub``
* ``__c11_atomic_fetch_and``
* ``__c11_atomic_fetch_or``
* ``__c11_atomic_fetch_xor``
* ``__c11_atomic_fetch_max``
* ``__c11_atomic_fetch_min``
The macros ``__ATOMIC_RELAXED``, ``__ATOMIC_CONSUME``, ``__ATOMIC_ACQUIRE``,
``__ATOMIC_RELEASE``, ``__ATOMIC_ACQ_REL``, and ``__ATOMIC_SEQ_CST`` are
provided, with values corresponding to the enumerators of C11's
``memory_order`` enumeration.
(Note that Clang additionally provides GCC-compatible ``__atomic_*``
builtins and OpenCL 2.0 ``__opencl_atomic_*`` builtins. The OpenCL 2.0
atomic builtins are an explicit form of the corresponding OpenCL 2.0
builtin function, and are named with a ``__opencl_`` prefix. The macros
``__OPENCL_MEMORY_SCOPE_WORK_ITEM``, ``__OPENCL_MEMORY_SCOPE_WORK_GROUP``,
``__OPENCL_MEMORY_SCOPE_DEVICE``, ``__OPENCL_MEMORY_SCOPE_ALL_SVM_DEVICES``,
and ``__OPENCL_MEMORY_SCOPE_SUB_GROUP`` are provided, with values
corresponding to the enumerators of OpenCL's ``memory_scope`` enumeration.)
Low-level ARM exclusive memory builtins
---------------------------------------
Clang provides overloaded builtins giving direct access to the three key ARM
instructions for implementing atomic operations.
.. code-block:: c
T __builtin_arm_ldrex(const volatile T *addr);
T __builtin_arm_ldaex(const volatile T *addr);
int __builtin_arm_strex(T val, volatile T *addr);
int __builtin_arm_stlex(T val, volatile T *addr);
void __builtin_arm_clrex(void);
The types ``T`` currently supported are:
* Integer types with width at most 64 bits (or 128 bits on AArch64).
* Floating-point types
* Pointer types.
Note that the compiler does not guarantee it will not insert stores which clear
the exclusive monitor in between an ``ldrex`` type operation and its paired
``strex``. In practice this is only usually a risk when the extra store is on
the same cache line as the variable being modified and Clang will only insert
stack stores on its own, so it is best not to use these operations on variables
with automatic storage duration.
Also, loads and stores may be implicit in code written between the ``ldrex`` and
``strex``. Clang will not necessarily mitigate the effects of these either, so
care should be exercised.
For these reasons the higher level atomic primitives should be preferred where
possible.
Non-temporal load/store builtins
--------------------------------
Clang provides overloaded builtins allowing generation of non-temporal memory
accesses.
.. code-block:: c
T __builtin_nontemporal_load(T *addr);
void __builtin_nontemporal_store(T value, T *addr);
The types ``T`` currently supported are:
* Integer types.
* Floating-point types.
* Vector types.
Note that the compiler does not guarantee that non-temporal loads or stores
will be used.
C++ Coroutines support builtins
--------------------------------
.. warning::
This is a work in progress. Compatibility across Clang/LLVM releases is not
guaranteed.
Clang provides experimental builtins to support C++ Coroutines as defined by
https://wg21.link/P0057. The following four are intended to be used by the
standard library to implement `std::experimental::coroutine_handle` type.
**Syntax**:
.. code-block:: c
void __builtin_coro_resume(void *addr);
void __builtin_coro_destroy(void *addr);
bool __builtin_coro_done(void *addr);
void *__builtin_coro_promise(void *addr, int alignment, bool from_promise)
**Example of use**:
.. code-block:: c++
template <> struct coroutine_handle<void> {
void resume() const { __builtin_coro_resume(ptr); }
void destroy() const { __builtin_coro_destroy(ptr); }
bool done() const { return __builtin_coro_done(ptr); }
// ...
protected:
void *ptr;
};
template <typename Promise> struct coroutine_handle : coroutine_handle<> {
// ...
Promise &promise() const {
return *reinterpret_cast<Promise *>(
__builtin_coro_promise(ptr, alignof(Promise), /*from-promise=*/false));
}
static coroutine_handle from_promise(Promise &promise) {
coroutine_handle p;
p.ptr = __builtin_coro_promise(&promise, alignof(Promise),
/*from-promise=*/true);
return p;
}
};
Other coroutine builtins are either for internal clang use or for use during
development of the coroutine feature. See `Coroutines in LLVM
<https://llvm.org/docs/Coroutines.html#intrinsics>`_ for
more information on their semantics. Note that builtins matching the intrinsics
that take token as the first parameter (llvm.coro.begin, llvm.coro.alloc,
llvm.coro.free and llvm.coro.suspend) omit the token parameter and fill it to
an appropriate value during the emission.
**Syntax**:
.. code-block:: c
size_t __builtin_coro_size()
void *__builtin_coro_frame()
void *__builtin_coro_free(void *coro_frame)
void *__builtin_coro_id(int align, void *promise, void *fnaddr, void *parts)
bool __builtin_coro_alloc()
void *__builtin_coro_begin(void *memory)
void __builtin_coro_end(void *coro_frame, bool unwind)
char __builtin_coro_suspend(bool final)
bool __builtin_coro_param(void *original, void *copy)
Note that there is no builtin matching the `llvm.coro.save` intrinsic. LLVM
automatically will insert one if the first argument to `llvm.coro.suspend` is
token `none`. If a user calls `__builin_suspend`, clang will insert `token none`
as the first argument to the intrinsic.
Source location builtins
------------------------
Clang provides experimental builtins to support C++ standard library implementation
of ``std::experimental::source_location`` as specified in http://wg21.link/N4600.
With the exception of ``__builtin_COLUMN``, these builtins are also implemented by
GCC.
**Syntax**:
.. code-block:: c
const char *__builtin_FILE();
const char *__builtin_FUNCTION();
unsigned __builtin_LINE();
unsigned __builtin_COLUMN(); // Clang only
**Example of use**:
.. code-block:: c++
void my_assert(bool pred, int line = __builtin_LINE(), // Captures line of caller
const char* file = __builtin_FILE(),
const char* function = __builtin_FUNCTION()) {
if (pred) return;
printf("%s:%d assertion failed in function %s\n", file, line, function);
std::abort();
}
struct MyAggregateType {
int x;
int line = __builtin_LINE(); // captures line where aggregate initialization occurs
};
static_assert(MyAggregateType{42}.line == __LINE__);
struct MyClassType {
int line = __builtin_LINE(); // captures line of the constructor used during initialization
constexpr MyClassType(int) { assert(line == __LINE__); }
};
**Description**:
The builtins ``__builtin_LINE``, ``__builtin_FUNCTION``, and ``__builtin_FILE`` return
the values, at the "invocation point", for ``__LINE__``, ``__FUNCTION__``, and
``__FILE__`` respectively. These builtins are constant expressions.
When the builtins appear as part of a default function argument the invocation
point is the location of the caller. When the builtins appear as part of a
default member initializer, the invocation point is the location of the
constructor or aggregate initialization used to create the object. Otherwise
the invocation point is the same as the location of the builtin.
When the invocation point of ``__builtin_FUNCTION`` is not a function scope the
empty string is returned.
Alignment builtins
------------------
Clang provides builtins to support checking and adjusting alignment of
pointers and integers.
These builtins can be used to avoid relying on implementation-defined behavior
of arithmetic on integers derived from pointers.
Additionally, these builtins retain type information and, unlike bitwise
arithmetic, they can perform semantic checking on the alignment value.
**Syntax**:
.. code-block:: c
Type __builtin_align_up(Type value, size_t alignment);
Type __builtin_align_down(Type value, size_t alignment);
bool __builtin_is_aligned(Type value, size_t alignment);
**Example of use**:
.. code-block:: c++
char* global_alloc_buffer;
void* my_aligned_allocator(size_t alloc_size, size_t alignment) {
char* result = __builtin_align_up(global_alloc_buffer, alignment);
// result now contains the value of global_alloc_buffer rounded up to the
// next multiple of alignment.
global_alloc_buffer = result + alloc_size;
return result;
}
void* get_start_of_page(void* ptr) {
return __builtin_align_down(ptr, PAGE_SIZE);
}
void example(char* buffer) {
if (__builtin_is_aligned(buffer, 64)) {
do_fast_aligned_copy(buffer);
} else {
do_unaligned_copy(buffer);
}
}
// In addition to pointers, the builtins can also be used on integer types
// and are evaluatable inside constant expressions.
static_assert(__builtin_align_up(123, 64) == 128, "");
static_assert(__builtin_align_down(123u, 64) == 64u, "");
static_assert(!__builtin_is_aligned(123, 64), "");
**Description**:
The builtins ``__builtin_align_up``, ``__builtin_align_down``, return their
first argument aligned up/down to the next multiple of the second argument.
If the value is already sufficiently aligned, it is returned unchanged.
The builtin ``__builtin_is_aligned`` returns whether the first argument is
aligned to a multiple of the second argument.
All of these builtins expect the alignment to be expressed as a number of bytes.
These builtins can be used for all integer types as well as (non-function)
pointer types. For pointer types, these builtins operate in terms of the integer
address of the pointer and return a new pointer of the same type (including
qualifiers such as ``const``) with an adjusted address.
When aligning pointers up or down, the resulting value must be within the same
underlying allocation or one past the end (see C17 6.5.6p8, C++ [expr.add]).
This means that arbitrary integer values stored in pointer-type variables must
not be passed to these builtins. For those use cases, the builtins can still be
used, but the operation must be performed on the pointer cast to ``uintptr_t``.
If Clang can determine that the alignment is not a power of two at compile time,
it will result in a compilation failure. If the alignment argument is not a
power of two at run time, the behavior of these builtins is undefined.
Non-standard C++11 Attributes
=============================
Clang's non-standard C++11 attributes live in the ``clang`` attribute
namespace.
Clang supports GCC's ``gnu`` attribute namespace. All GCC attributes which
are accepted with the ``__attribute__((foo))`` syntax are also accepted as
``[[gnu::foo]]``. This only extends to attributes which are specified by GCC
(see the list of `GCC function attributes
<https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html>`_, `GCC variable
attributes <https://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html>`_, and
`GCC type attributes
<https://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html>`_). As with the GCC
implementation, these attributes must appertain to the *declarator-id* in a
declaration, which means they must go either at the start of the declaration or
immediately after the name being declared.
For example, this applies the GNU ``unused`` attribute to ``a`` and ``f``, and
also applies the GNU ``noreturn`` attribute to ``f``.
.. code-block:: c++
[[gnu::unused]] int a, f [[gnu::noreturn]] ();
Target-Specific Extensions
==========================
Clang supports some language features conditionally on some targets.
ARM/AArch64 Language Extensions
-------------------------------
Memory Barrier Intrinsics
^^^^^^^^^^^^^^^^^^^^^^^^^
Clang implements the ``__dmb``, ``__dsb`` and ``__isb`` intrinsics as defined
in the `ARM C Language Extensions Release 2.0
<http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf>`_.
Note that these intrinsics are implemented as motion barriers that block
reordering of memory accesses and side effect instructions. Other instructions
like simple arithmetic may be reordered around the intrinsic. If you expect to
have no reordering at all, use inline assembly instead.
X86/X86-64 Language Extensions
------------------------------
The X86 backend has these language extensions:
Memory references to specified segments
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Annotating a pointer with address space #256 causes it to be code generated
relative to the X86 GS segment register, address space #257 causes it to be
relative to the X86 FS segment, and address space #258 causes it to be
relative to the X86 SS segment. Note that this is a very very low-level
feature that should only be used if you know what you're doing (for example in
an OS kernel).
Here is an example:
.. code-block:: c++
#define GS_RELATIVE __attribute__((address_space(256)))
int foo(int GS_RELATIVE *P) {
return *P;
}
Which compiles to (on X86-32):