[CMake] Check for problematic MSVC + /arch:AVX configuration

[thieta]

Summary

Add a new CMake file to expand on for more problematic configurations
in the future.

Related to #54645

[thieta]

Ping on this one - any thoughts?

[RKSimon]

I'd like this to go in as we have so little control over the MSVC crash (and have struggled to even reduce the repro), but I'm not an expert on cmake or llvm's cmake style

[beanz]

This looks good to me and seems like a good added check.

@compnerd, @phosek or @smeenai may have thoughts too.

[smeenai]

LGTM!

llvm/cmake/modules/CheckProblematicConfigurations.cmake

3

Maybe "allow" would be better than "force"? "force" kinda sounds like the build system will purposely use a problematic toolchain configuration if you turn the flag on.

18

Might be nice to reference the bug URL in the message as well.

[phosek]

LGTM

llvm/cmake/modules/CheckProblematicConfigurations.cmake

5

We usually use lower_case for the names of functions and macros.

[thieta]

Review fixes

[thakis]

In case it helps anyone in the future:

I ran

% /Applications/CMake.app/Contents/bin/cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ENABLE_PROJECTS='clang;lld' -DLLVM_ENABLE_RUNTIMES='compiler-rt' -DLLVM_APPEND_VC_REV=NO -DLLVM_TARGETS_TO_BUILD='X86' ../llvm-project/llvm

followed by

% ninja runtimes

<y build eventually failed with:

...
[2736/2740] Performing configure step for 'runtimes'
-- Linker detection: ld64
CMake Error at /Users/thakis/src/llvm-project/llvm/cmake/modules/CheckProblematicConfigurations.cmake:14 (if):
  if given arguments:

    "STREQUAL" "MSVC"

  Unknown arguments specified
Call Stack (most recent call first):
  /Users/thakis/src/llvm-project/llvm/cmake/modules/HandleLLVMOptions.cmake:10 (include)
  CMakeLists.txt:149 (include)

That error went away with the obvious patch [1], but then things failed later like so:

CMake Error at /Users/thakis/src/llvm-project/compiler-rt/CMakeLists.txt:450 (message):
  -g is not supported by host compiler

The problem was that I'm on an arm64 system but didn't include AArch64 in LLVM_TARGETS_TO_BUILD, so runtimes/runtimes-bins/CMakeFiles/CMakeError.log ended up with lots of error: unable to create target: 'No available targets are compatible with triple "arm64-apple-macosx12.0.0"'.

The fix, of course, was to add both ARM and AArch64 to LLVM_TARGETS_TO_BUILD in addition to X86 (-DLLVM_TARGETS_TO_BUILD='X86;ARM;AArch64'), and clobbering the "runtimes" dir in the build dir so that cmake picks it up.

(Adding just AArch64 lead to error: unable to create target: 'No available targets are compatible with triple "thumbv7em-apple-unknown-macho"').

1:

% git diff
diff --git a/llvm/cmake/modules/CheckProblematicConfigurations.cmake b/llvm/cmake/modules/CheckProblematicConfigurations.cmake
index e133873d756c..71484172cfb6 100644
--- a/llvm/cmake/modules/CheckProblematicConfigurations.cmake
+++ b/llvm/cmake/modules/CheckProblematicConfigurations.cmake
@@ -11,7 +11,7 @@ endmacro()
 
 # MSVC and /arch:AVX is untested and have created problems before. See:
 # https://github.com/llvm/llvm-project/issues/54645
-if(${CMAKE_CXX_COMPILER_ID} STREQUAL MSVC)
+if("${CMAKE_CXX_COMPILER_ID}" STREQUAL MSVC)
   string(TOLOWER "${CMAKE_CXX_FLAGS} ${CMAKE_C_FLAGS}" _FLAGS)
   if(_FLAGS MATCHES "/arch:avx[0-9]*")
     log_problematic("Compiling LLVM with MSVC and the /arch:AVX flag is known to cause issues with parts of LLVM.\nSee https://github.com/llvm/llvm-project/issues/54645 for details.\nUse clang-cl if you want to enable AVX instructions.")

(Posting this here since the first symptom of my mistake led me to this patch. It's innocent, but it's where I looked first, so maybe this helps someone else.)

llvm/cmake/config-ix.cmake

 if( WIN32 AND NOT CYGWIN )
   # We consider Cygwin as another Unix
   set(PURE_WINDOWS 1)
 endif()
 
 include(CheckIncludeFile)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckFunctionExists)
 include(CheckStructHasMember)
 include(CheckCCompilerFlag)
 include(CMakePushCheckState)
 
 include(CheckCompilerVersion)
+include(CheckProblematicConfigurations)
 include(HandleLLVMStdlib)
 
 if( UNIX AND NOT (APPLE OR BEOS OR HAIKU) )
   # Used by check_symbol_exists:
   list(APPEND CMAKE_REQUIRED_LIBRARIES "m")
 endif()
 # x86_64 FreeBSD 9.2 requires libcxxrt to be specified explicitly.
 if( CMAKE_SYSTEM MATCHES "FreeBSD-9.2-RELEASE" AND

llvm/cmake/modules/CheckProblematicConfigurations.cmake

+
+option(LLVM_ALLOW_PROBLEMATIC_CONFIGURATIONS OFF "Set this option to ON to allow problematic toolchain configurations. Use on your own risk.")
+
+macro(log_problematic MESSAGE)
+  if(LLVM_ALLOW_PROBLEMATIC_CONFIGURATIONS)
+    message(WARNING "${MESSAGE}")
+  else()
+    message(FATAL_ERROR "${MESSAGE}\nYou can force usage of this configuration by passing -DLLVM_ALLOW_PROBLEMATIC_CONFIGURATIONS=ON")
+  endif()
+endmacro()
+
+# MSVC and /arch:AVX is untested and have created problems before. See:
+# https://github.com/llvm/llvm-project/issues/54645
+if(${CMAKE_CXX_COMPILER_ID} STREQUAL MSVC)
+  string(TOLOWER "${CMAKE_CXX_FLAGS} ${CMAKE_C_FLAGS}" _FLAGS)
+  if(_FLAGS MATCHES "/arch:avx[0-9]*")
+    log_problematic("Compiling LLVM with MSVC and the /arch:AVX flag is known to cause issues with parts of LLVM.\nSee https://github.com/llvm/llvm-project/issues/54645 for details.\nUse clang-cl if you want to enable AVX instructions.")
+  endif()
+endif()

llvm/cmake/modules/HandleLLVMOptions.cmake

 # This CMake module is responsible for interpreting the user defined LLVM_
 # options and executing the appropriate CMake commands to realize the users'
 # selections.
 
 # This is commonly needed so make sure it's defined before we include anything
 # else.
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 
 include(CheckCompilerVersion)
+include(CheckProblematicConfigurations)
 include(HandleLLVMStdlib)
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckSymbolExists)
 include(CMakeDependentOption)
 include(LLVMProcessSources)
 
 if(CMAKE_LINKER MATCHES ".*lld" OR (LLVM_USE_LINKER STREQUAL "lld" OR LLVM_ENABLE_LLD))