https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/106843
Backport 68d8b3846ab1e6550910f2a9a685690eee558af2 Requested by: @overmighty >From c58828b0d1ee256991f907bc25d827e4c8ab4ba9 Mon Sep 17 00:00:00 2001 From: OverMighty <its.overmig...@gmail.com> Date: Fri, 30 Aug 2024 12:59:05 +0200 Subject: [PATCH] [builtins] Fix missing main() function in float16/bfloat16 support checks (#104478) The CMake docs state that `check_c_source_compiles()` checks whether the supplied code "can be compiled as a C source file and linked as an executable (so it must contain at least a `main()` function)." https://cmake.org/cmake/help/v3.30/module/CheckCSourceCompiles.html In practice, this command is a wrapper around `try_compile()`: - https://gitlab.kitware.com/cmake/cmake/blob/2904ce00d2ed6ad5dac6d3459af62d8223e06ce0/Modules/CheckCSourceCompiles.cmake#L54 - https://gitlab.kitware.com/cmake/cmake/blob/2904ce00d2ed6ad5dac6d3459af62d8223e06ce0/Modules/Internal/CheckSourceCompiles.cmake#L101 When `CMAKE_SOURCE_DIR` is compiler-rt/lib/builtins/, `CMAKE_TRY_COMPILE_TARGET_TYPE` is set to `STATIC_LIBRARY`, so the checks for `float16` and `bfloat16` support work as intended in a Clang + compiler-rt runtime build for example, as it runs CMake recursively from that directory. However, when using llvm/ or compiler-rt/ as CMake source directory, as `CMAKE_TRY_COMPILE_TARGET_TYPE` defaults to `EXECUTABLE`, these checks will indeed fail if the code doesn't have a `main()` function. This results in LLVM using x86 SIMD registers when generating calls to builtins that, with Arch Linux's compiler-rt package for example, actually use a GPR for their argument or return value as they use `uint16_t` instead of `_Float16`. This had been caught in post-commit review: https://reviews.llvm.org/D145237#4521152. Use of the internal `CMAKE_C_COMPILER_WORKS` variable is not what hides the issue, however. PR #69842 tried to fix this by unconditionally setting `CMAKE_TRY_COMPILE_TARGET_TYPE` to `STATIC_LIBRARY`, but it apparently caused other issues, so it was reverted. This PR just adds a `main()` function in the checks, as per the CMake docs. (cherry picked from commit 68d8b3846ab1e6550910f2a9a685690eee558af2) --- compiler-rt/lib/builtins/CMakeLists.txt | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt index abea8c498f7bdc..e0b2d08c207754 100644 --- a/compiler-rt/lib/builtins/CMakeLists.txt +++ b/compiler-rt/lib/builtins/CMakeLists.txt @@ -867,10 +867,12 @@ else () endif() endif() endif() - check_c_source_compiles("_Float16 foo(_Float16 x) { return x; }" + check_c_source_compiles("_Float16 foo(_Float16 x) { return x; } + int main(void) { return 0; }" COMPILER_RT_HAS_${arch}_FLOAT16) append_list_if(COMPILER_RT_HAS_${arch}_FLOAT16 -DCOMPILER_RT_HAS_FLOAT16 BUILTIN_CFLAGS_${arch}) - check_c_source_compiles("__bf16 foo(__bf16 x) { return x; }" + check_c_source_compiles("__bf16 foo(__bf16 x) { return x; } + int main(void) { return 0; }" COMPILER_RT_HAS_${arch}_BFLOAT16) # Build BF16 files only when "__bf16" is available. if(COMPILER_RT_HAS_${arch}_BFLOAT16) _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
