[libc-commits] [libc] [llvm] [libc][math] Refactor fmul-fsub-frexp family to header-only (PR #195431)

Sat May 2 02:54:40 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `libc-aarch64-ubuntu-dbg` running on `libc-aarch64-ubuntu` while building `libc,utils` at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/104/builds/47327

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (annotate) failure: 'python ../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py ...' (failure)
...
@@@BUILD_STEP build libc@@@
Running: ninja libc
[1/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.atan2f.dir/atan2f.cpp.o
[2/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.pow.dir/pow.cpp.o
[3/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.fsubl.dir/fsubl.cpp.o
[4/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.cbrt.dir/cbrt.cpp.o
[5/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.exp.dir/exp.cpp.o
[6/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpbf16.dir/frexpbf16.cpp.o
[7/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.exp10.dir/exp10.cpp.o
[8/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmul.dir/fmul.cpp.o
FAILED: libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmul.dir/fmul.cpp.o 
/usr/bin/clang++ -DLIBC_NAMESPACE=__llvm_libc_20_0_0_git -D_DEBUG -I/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc -isystem libc/include -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wstring-conversion -Wno-pass-failed -fdiagnostics-color -g -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_COPT_STRING_LENGTH_IMPL=clang_vector -DLIBC_COPT_FIND_FIRST_CHARACTER_IMPL=word -DLIBC_ADD_NULL_CHECKS -DLIBC_ERRNO_MODE=LIBC_ERRNO_MODE_DEFAULT -DLIBC_THREAD_MODE=LIBC_THREAD_MODE_PLATFORM -DLIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY -DLIBC_CONF_WCTYPE_MODE=LIBC_WCTYPE_MODE_ASCII -DLIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT=100 -fpie -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -fstack-protector-strong -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_COPT_PUBLIC_PACKAGING -std=gnu++17 -MD -MT libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmul.dir/fmul.cpp.o -MF libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmul.dir/fmul.cpp.o.d -o libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmul.dir/fmul.cpp.o -c /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/math/generic/fmul.cpp
In file included from /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/math/generic/fmul.cpp:10:
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/math/fmul.h:21:29: error: constexpr function never produces a constant expression [-Winvalid-constexpr]
LIBC_INLINE constexpr float fmul(double x, double y) {
                            ^
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/math/fmul.h:30:31: note: non-constexpr function 'exact_mult<double, 27>' cannot be used in a constant expression
  fputil::DoubleDouble prod = fputil::exact_mult(x, y);
                              ^
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu/llvm-project/libc/src/__support/FPUtil/double_double.h:132:42: note: declared here
LIBC_INLINE LIBC_CONSTEXPR NumberPair<T> exact_mult(T a, T b) {
                                         ^
1 error generated.
[9/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.hypotf.dir/hypotf.cpp.o
[10/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.exp2.dir/exp2.cpp.o
[11/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.atan2.dir/atan2.cpp.o
[12/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.asinpi.dir/asinpi.cpp.o
[13/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.atan.dir/atan.cpp.o
[14/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.asin.dir/asin.cpp.o
[15/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.sin.dir/sin.cpp.o
[16/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.powf.dir/powf.cpp.o
[17/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.log1p.dir/log1p.cpp.o
[18/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.frexpl.dir/frexpl.cpp.o
[19/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.cos.dir/cos.cpp.o
[20/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.acos.dir/acos.cpp.o
[21/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.fmull.dir/fmull.cpp.o
[22/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.expm1.dir/expm1.cpp.o
[23/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.tan.dir/tan.cpp.o
[24/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.sincos.dir/sincos.cpp.o
[25/33] Building CXX object libc/src/math/generic/CMakeFiles/libc.src.math.generic.atan2f128.dir/atan2f128.cpp.o
ninja: build stopped: subcommand failed.
['ninja', 'libc'] exited with return code 1.
The build step threw an exception...
Traceback (most recent call last):
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 181, in step
    yield
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 143, in main
    run_command(['ninja', 'libc'])
  File "../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py", line 196, in run_command

```

</details>

https://github.com/llvm/llvm-project/pull/195431