[compiler-rt][builtins] Fix FLOAT16 feature detection

[littlewu2508]

I'm submitting this patch authored by @tstellar:

CMAKE_TRY_COMPILE_TARGET_TYPE defaults to EXECUTABLE, which causes any feature detection code snippet without a main function to fail, so we need to make sure it gets explicitly set to STATIC_LIBRARY.

I think maybe it should be up-streamed, since it causes some issues [1,2] in some distros. Please have a review to see whether this patch should be applied in upstream, or just in distro.

[1] ROCm/rocFFT#439
[2] ROCm/rocBLAS#1350

[tstellar]

This fixed a bug in the compiler-rt build configuration that we use in Fedora. I have no idea if this is correct for all build configurations.

[littlewu2508]

This fixed a bug in the compiler-rt build configuration that we use in Fedora. I have no idea if this is correct for all build configurations.

I think, unless there's a reason that when CMAKE_SOURCE_DIR != CMAKE_CURRENT_SOURCE_DIR, which is the case for Fedora and Gentoo, it (in general) has to be non-static, then there's no reason we should put STATIC_LIBRARY inside that if branch.

And if there are scenarios STATIC_LIBRARY should not be set, then maybe the if branch excludes too much cases (Fedora and Gentoo's build configuration), unless our build configuration turned out to be somewhat "incompatible" or "wrong"

[mgorny]

LGTM.

[littlewu2508]

Hi, @tstellar should we proceed merging this PR?

[tstellar]

@littlewu2508 What build configurations have you tested this with?

[littlewu2508]

@littlewu2508 What build configurations have you tested this with?

Gentoo is building compiler-rt as a standalone project. The invoked cmake command on my machine is:

cmake -C /run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_common_config.cmake -G Ninja -DCMAKE_INSTALL_PREFIX=/opt/gentoo/usr -DCOMPILER_RT_INSTALL_PATH=/opt/gentoo/usr/lib/clang/17 -DCOMPILER_RT_INCLUDE_TESTS=no -DCOMPILER_RT_BUILD_LIBFUZZER=OFF -DCOMPILER_RT_BUILD_MEMPROF=OFF -DCOMPILER_RT_BUILD_ORC=OFF -DCOMPILER_RT_BUILD_PROFILE=OFF -DCOMPILER_RT_BUILD_SANITIZERS=OFF -DCOMPILER_RT_BUILD_XRAY=OFF -DPython3_EXECUTABLE=/opt/gentoo/usr/bin/python3.12 -DCAN_TARGET_i386=no -DCAN_TARGET_x86_64=yes -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_TOOLCHAIN_FILE=/run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_toolchain.cmake /run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt

And

gentoo_common_config.cmake is

set(CMAKE_GENTOO_BUILD ON CACHE BOOL "Indicate Gentoo package build")
set(LIB_SUFFIX 64 CACHE STRING "library path suffix" FORCE)
set(CMAKE_INSTALL_LIBDIR lib64 CACHE PATH "Output directory for libraries")
set(CMAKE_INSTALL_INFODIR "/opt/gentoo/usr/share/info" CACHE PATH "")
set(CMAKE_INSTALL_MANDIR "/opt/gentoo/usr/share/man" CACHE PATH "")
set(CMAKE_USER_MAKE_RULES_OVERRIDE "/run/user/18014/portage/sys-libs/compiler-rt-17.0.4/work/compiler-rt-17.0.4_build/gentoo_rules.cmake" CACHE FILEPATH "Gentoo override rules")
set(CMAKE_INSTALL_DOCDIR "/opt/gentoo/usr/share/doc/compiler-rt-17.0.4" CACHE PATH "")
set(BUILD_SHARED_LIBS ON CACHE BOOL "")
set(Python3_FIND_UNVERSIONED_NAMES FIRST CACHE STRING "")
set(CMAKE_INSTALL_ALWAYS 1)
set(CMAKE_ASM_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_ASM-ATT_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_C_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_MODULE_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")
set(CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO "" CACHE STRING "")

while gentoo_toolchain.cmake is

set(CMAKE_ASM_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_ASM-ATT_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_C_COMPILER "x86_64-pc-linux-gnu-clang")
set(CMAKE_CXX_COMPILER "x86_64-pc-linux-gnu-clang++")
set(CMAKE_Fortran_COMPILER "x86_64-pc-linux-gnu-gfortran")
set(CMAKE_AR /opt/gentoo/usr/bin/x86_64-pc-linux-gnu-ar CACHE FILEPATH "Archive manager" FORCE)
set(CMAKE_RANLIB /opt/gentoo/usr/bin/x86_64-pc-linux-gnu-ranlib CACHE FILEPATH "Archive index generator" FORCE)
set(CMAKE_SYSTEM_PROCESSOR "x86_64")

[thesamesam]

Now that 18 is branched, I think we should just try this.

[gulfemsavrun]

We started seeing SanitizerCommon-tsan test failures after this patch in our Clang Linux builders.

FAIL: SanitizerCommon-tsan-x86_64-Linux :: Linux/abort_on_error.cpp (3645 of 15728)
******************** TEST 'SanitizerCommon-tsan-x86_64-Linux :: Linux/abort_on_error.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 4: /b/s/w/ir/x/w/llvm_build/./bin/clang  --driver-mode=g++ -gline-tables-only -fsanitize=thread  -funwind-tables --sysroot=/b/s/w/ir/x/w/cipd/linux  -I/b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test -ldl /b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test/sanitizer_common/TestCases/Linux/abort_on_error.cpp -o /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/test/sanitizer_common/tsan-x86_64-Linux/Linux/Output/abort_on_error.cpp.tmp
+ /b/s/w/ir/x/w/llvm_build/./bin/clang --driver-mode=g++ -gline-tables-only -fsanitize=thread -funwind-tables --sysroot=/b/s/w/ir/x/w/cipd/linux -I/b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test -ldl /b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test/sanitizer_common/TestCases/Linux/abort_on_error.cpp -o /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/test/sanitizer_common/tsan-x86_64-Linux/Linux/Output/abort_on_error.cpp.tmp
ld.lld: error: undefined symbol: __gcc_personality_v0
>>> referenced by abort_on_error.cpp
>>>               /b/s/w/ir/x/t/lit-tmp-ltnvtf5j/abort_on_error-0ca4b8.o:(DW.ref.__gcc_personality_v0)
clang: error: linker command failed with exit code 1 (use -v to see invocation)

--

********************

https://logs.chromium.org/logs/fuchsia/led/gulfem_google.com/141f7eb5f57d1686c0532c0155e6deca355b20629e48dedea6078c47d6e7a825/+/u/clang/test/stdout

[tstellar]

Can you revert this. I don't think this was sufficiently reivewed.

[tstellar]

Reverted in f6ca6ed.

[thesamesam]

Thanks.

[tstellar]

This needs to be reviewed by someone familiar with the compiler-rt build system.

[kwk]

This needs to be reviewed by someone familiar with the compiler-rt build system.

@tstellar is there any progress on this? Without this PR this test fails for us: https://src.fedoraproject.org/tests/compiler-rt/blob/main/f/fp16-abi

To reproduce it locally with a recent clang you can do this:

$ cat <<EOF > /tmp/test.cpp                                           
#include <iostream>
#include <algorithm>
#include <vector>

int main()
{
    _Float16 one_f16 = 0.123;
    float one_f32 = one_f16;
    std::cout <<  one_f32 << std::endl;
    return 0;
}
EOF
$ clang++ --rtlib=compiler-rt -O0 /tmp/test.cpp -o /tmp/test
$ /tmp/test

The expected output is 0.122986 but the actual output is 5.96046e-08. This only happens for -O0 by the way.

For the moment I'm going to cherry-pick this PR and have it applied to our snapshot builds.