Warn about unsupported ibmlongdouble

[tuliom]

Summary

When -mabi=ieeelongdouble is enabled by default, libc++ does not support
-mabi=ibmlongdouble.

[nikic]

Can you please upload the patch with full context (-U99999)?

The assumption here is that libc++ is being compiled with a compiler that has the same ieeelongdouble default as the clang that is being built, right? I guess that's the most reasonable assumption one can make.

[MaskRay]

clang/lib/Driver/ToolChains/PPCLinux.h

30

New functions should use camelCase

[tuliom]

I'm attaching a new version of the patch.

Can you please upload the patch with full context (-U99999)?

@nikic Done!

The assumption here is that libc++ is being compiled with a compiler that has the same ieeelongdouble default as the clang that is being built, right?

@nikic Right.

New functions should use camelCase

@MaskRay Fixed.

[nikic]

clang/lib/Driver/ToolChains/PPCLinux.cpp

75

I don't think this formatting is right. You may find clang/tools/clang-format/clang-format-diff.py helpful.

I use this script locally:

#!/bin/sh
git diff -U ${1:-HEAD} | clang/tools/clang-format/clang-format-diff.py -p1

And then do something like ./clang_format_diff.sh | patch -p0 after checking that it did not reformat too much.

clang/test/Driver/lit.local.cfg

25

I believe this isn't robust, because ON is not the only possible value. Instead, you'll want to canonicalize the variable: https://github.com/llvm/llvm-project/blob/03e6d9d9d1d48e43f3efc35eb75369b90d4510d5/clang/test/CMakeLists.txt#L4

[qiucf]

Thanks for the patch! But does libc++ support to be built with -mabi=ieeelongdouble now? (like libstdc++, if it works correctly, it should co-exist and be linked with different long double ABIs)

clang/lib/Driver/ToolChains/PPCLinux.cpp

96

SupportIEEEFloat128 checks the library version:

• If using libstdc++, then libstdc++ (GCC) >= 12.1.0 is okay.
• If using libc++, then sorry, no libc++ supports -mabi=ieeelongdouble now.
• Glibc should >= 2.32

If the assumptions are still right, this changes its meaning (and supportIBMLongDouble has different meaning from it).

clang/test/Driver/lit.local.cfg

26

Can we assume if we are compiling with -mabi=ieeelongdouble, then libc++ 'must' be built with the same long double ABI? If I understand correctly, they're unrelated.

[tuliom]

In D139450#3981486, @qiucf wrote:

Thanks for the patch! But does libc++ support to be built with -mabi=ieeelongdouble now?

@qiucf libc++ can be built with -mabi=ieeelongdouble, but it supports only a single long double format, i.e. if it's built with -mabi=ieeelongdouble, it won't support IBM double-double and vice versa.
This is already being used in Fedora Rawhide at the moment.

[tuliom]

Fix the issues pointed by @nikic.

[tuliom]

clang/lib/Driver/ToolChains/PPCLinux.cpp

75

Thanks, this pointed out 2 errors.

96

@qiucf In operating systems that switched to IEEE long double by default, all libraries (and programs) are built with IEEE long double, including libc++.

clang/test/Driver/lit.local.cfg

25

Changed. This caused a few other modifications in the latest revision.

26

@qiucf I didn't understand this part. Are you suggesting to remove the long double warnings because the way the compiler was built is unrelated to the way libc++ was built?

[qiucf]

clang/test/Driver/lit.local.cfg

26

Ah, I misunderstood meaning of 'defaults to IEEE long double' in last review. We can assume 'how the compiler was built' is the same as 'how the libc++ was built'.

But when 'how the libc++ was built' conflicts with 'how the compiler compiles current program', we expect a warning, right? If so, this looks reasonable.

[tuliom]

clang/test/Driver/lit.local.cfg

26

Yes, exactly.
Thanks!

[tuliom]

Thanks @qiucf ! I don't have commit access yet. Could you land this patch for me, please?
Please use “Tulio Magno Quites Machado Filho [e-mail]” to commit the change.

[qiucf]

Committed as https://github.com/llvm/llvm-project/commit/5f68c4111ab9c79b902723df3986dd1033813c01

ppc-float-abi-warning.cpp would fail when testing on machine with glibc older than 2.32 but PPC_LINUX_DEFAULT_IEEELONGDOUBLE enabled, which is known failure even before this patch.

clang/lib/Driver/ToolChains/PPCLinux.h

public:
 
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
 private:
   bool SupportIEEEFloat128(const Driver &D, const llvm::Triple &Triple,
                            const llvm::opt::ArgList &Args) const;
+  bool supportIBMLongDouble(const Driver &D,
+                            const llvm::opt::ArgList &Args) const;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_PPC_LINUX_H

clang/lib/Driver/ToolChains/PPCLinux.cpp

 }
 
 PPCLinuxToolChain::PPCLinuxToolChain(const Driver &D,
                                      const llvm::Triple &Triple,
                                      const llvm::opt::ArgList &Args)
     : Linux(D, Triple, Args) {
   if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
     StringRef ABIName = A->getValue();
-    if (ABIName == "ieeelongdouble" && !SupportIEEEFloat128(D, Triple, Args))
+
+    if ((ABIName == "ieeelongdouble" &&
+         !SupportIEEEFloat128(D, Triple, Args)) ||
+        (ABIName == "ibmlongdouble" && !supportIBMLongDouble(D, Args)))
       D.Diag(diag::warn_drv_unsupported_float_abi_by_lib) << ABIName;
   }
 }
 
 void PPCLinuxToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                                   ArgStringList &CC1Args) const {
   if (!DriverArgs.hasArg(clang::driver::options::OPT_nostdinc) &&
       !DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     const Driver &D = getDriver();
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include", "ppc_wrappers");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   Linux::AddClangSystemIncludeArgs(DriverArgs, CC1Args);
 }
 
+bool PPCLinuxToolChain::supportIBMLongDouble(
+    const Driver &D, const llvm::opt::ArgList &Args) const {
+  if (Args.hasArg(options::OPT_nostdlib, options::OPT_nostdlibxx))
+    return true;
+
+  CXXStdlibType StdLib = ToolChain::GetCXXStdlibType(Args);
+  if (StdLib == CST_Libstdcxx)
+    return true;
+
+  return StdLib == CST_Libcxx && !defaultToIEEELongDouble();
+}
+
 bool PPCLinuxToolChain::SupportIEEEFloat128(
     const Driver &D, const llvm::Triple &Triple,
     const llvm::opt::ArgList &Args) const {
   if (!Triple.isLittleEndian() || !Triple.isPPC64())
     return false;
 
   if (Args.hasArg(options::OPT_nostdlib, options::OPT_nostdlibxx))
     return true;
 
   CXXStdlibType StdLib = ToolChain::GetCXXStdlibType(Args);
   bool HasUnsupportedCXXLib =
-      StdLib == CST_Libcxx ||
+      (StdLib == CST_Libcxx && !defaultToIEEELongDouble()) ||
       (StdLib == CST_Libstdcxx &&
        GCCInstallation.getVersion().isOlderThan(12, 1, 0));
 
   std::string Linker = Linux::getDynamicLinker(Args);
   return GlibcSupportsFloat128((Twine(D.DyldPrefix) + Linker).str()) &&
          !(D.CCCIsCXX() && HasUnsupportedCXXLib);
 }

clang/test/CMakeLists.txt

llvm_canonicalize_cmake_booleans(
   CLANG_PLUGIN_SUPPORT
   CLANG_SPAWN_CC1
   ENABLE_BACKTRACES
   LLVM_ENABLE_ZLIB
   LLVM_ENABLE_ZSTD
   LLVM_ENABLE_PER_TARGET_RUNTIME_DIR
   LLVM_ENABLE_THREADS
   LLVM_WITH_Z3
+  PPC_LINUX_DEFAULT_IEEELONGDOUBLE
   )
 
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
   MAIN_CONFIG
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
   PATHS

clang/test/Driver/lit.local.cfg

driver_overwrite_env_vars = ['MACOSX_DEPLOYMENT_TARGET',
                              'CC_LOG_DIAGNOSTICS', 'CC_PRINT_PROC_STAT']
 
 for name in driver_overwrite_env_vars:
   if name in config.environment:
     del config.environment[name]
 
 if llvm_config.use_lld(required=False):
     config.available_features.add('lld')
+
+if config.ppc_linux_default_ieeelongdouble:
+  config.available_features.add('ppc_linux_default_ieeelongdouble')

clang/test/Driver/ppc-float-abi-warning.cpp

 // REQUIRES: powerpc-registered-target
 // RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s \
 // RUN:  --gcc-toolchain=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-11.2.0 \
 // RUN:  -mabi=ieeelongdouble -stdlib=libstdc++ 2>&1 | FileCheck %s
 // RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s \
 // RUN:  --gcc-toolchain=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-12 \
 // RUN:  --dyld-prefix=%S/Inputs/powerpc64le-linux-gnu-tree/gcc-12 \
 // RUN:  -mabi=ieeelongdouble -stdlib=libstdc++ 2>&1 | \
 // RUN:  FileCheck %s --check-prefix=NOWARN
-// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s \
-// RUN:  -mabi=ieeelongdouble -stdlib=libc++ 2>&1 | FileCheck %s
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
+// RUN:  -stdlib=libc++ 2>&1 | \
+// RUN:  FileCheck %s --check-prefix=NOWARN
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
+// RUN:  -mabi=ibmlongdouble -stdlib=libc++ -Wno-unsupported-abi 2>&1 | \
+// RUN:  FileCheck %s --check-prefix=NOWARN
 // RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
 // RUN:  -mabi=ieeelongdouble -stdlib=libc++ -Wno-unsupported-abi 2>&1 | \
 // RUN:  FileCheck %s --check-prefix=NOWARN
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
+// RUN:  -mabi=%if ppc_linux_default_ieeelongdouble %{ieeelongdouble%} \
+// RUN:  %else %{ibmlongdouble%} -stdlib=libc++ 2>&1 | \
+// RUN:  FileCheck %s --check-prefix=NOWARN
+// RUN: %clang -### --driver-mode=g++ -target powerpc64le-linux-gnu %s\
+// RUN:  -mabi=%if ppc_linux_default_ieeelongdouble %{ibmlongdouble%} \
+// RUN:  %else %{ieeelongdouble%} -stdlib=libc++ 2>&1 | FileCheck %s
 
-// CHECK: warning: float ABI 'ieeelongdouble' is not supported by current library
-// NOWARN-NOT: warning: float ABI 'ieeelongdouble' is not supported by current library
+// CHECK: warning: float ABI '{{.*}}' is not supported by current library
+// NOWARN-NOT: warning: float ABI '{{.*}}' is not supported by current library
 long double foo(long double x) { return x; }

clang/test/lit.site.cfg.py.in

 config.enable_threads = @LLVM_ENABLE_THREADS@
 config.host_arch = "@HOST_ARCH@"
 config.python_executable = "@Python3_EXECUTABLE@"
 config.use_z3_solver = lit_config.params.get('USE_Z3_SOLVER', "@USE_Z3_SOLVER@")
 config.has_plugins = @CLANG_PLUGIN_SUPPORT@
 config.clang_vendor_uti = "@CLANG_VENDOR_UTI@"
 config.llvm_external_lit = path(r"@LLVM_EXTERNAL_LIT@")
 config.standalone_build = @CLANG_BUILT_STANDALONE@
+config.ppc_linux_default_ieeelongdouble = @PPC_LINUX_DEFAULT_IEEELONGDOUBLE@
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
 
 # Let the main config do the real work.
 lit_config.load_config(
     config, os.path.join(config.clang_src_dir, "test/lit.cfg.py"))