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[libc] Make LIBC_MATH_NO_ERRNO imply -fno-math-errno #125794

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Merged
merged 4 commits into from
Oct 16, 2025
Merged

[libc] Make LIBC_MATH_NO_ERRNO imply -fno-math-errno #125794

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6d9dac2
[libc] Make LIBC_MATH_NO_ERRNO imply `-fno-math-errno`
petrhosek Feb 5, 2025
92a0fd5
Move the check
petrhosek Feb 5, 2025
5688536
Merge remote-tracking branch 'origin/main' into libc-config-no-math-e…
petrhosek Oct 15, 2025
18520d4
Readd the null check
petrhosek Oct 15, 2025
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10 changes: 3 additions & 7 deletions libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -28,13 +28,6 @@ function(_get_compile_options_from_flags output_var)
elseif(LIBC_TARGET_ARCHITECTURE_IS_RISCV64)
list(APPEND compile_options "-D__LIBC_RISCV_USE_FMA")
endif()
# For clang, we will build the math functions with `-fno-math-errno` so that
# __builtin_fma* will generate the fused-mutliply-add instructions. We
# don't put the control flag to the public config yet, and see if it makes
# sense to just enable this flag by default.
if(LIBC_ADD_FNO_MATH_ERRNO)
list(APPEND compile_options "-fno-math-errno")
endif()
endif()
if(ADD_ROUND_OPT_FLAG)
if(LIBC_TARGET_ARCHITECTURE_IS_X86_64)
Expand Down Expand Up @@ -71,6 +64,9 @@ function(_get_compile_options_from_flags output_var)
"SHELL:-Xclang -target-feature -Xclang +fullfp16")
endif()
endif()
if(LIBC_CONF_MATH_OPTIMIZATIONS MATCHES "LIBC_MATH_NO_ERRNO")
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@lntue lntue Feb 5, 2025

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Can you move this to L101-ish, where LIBC_CONF_MATH_OPTIMIZATIONS is checked?

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@petrhosek petrhosek Feb 5, 2025

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Done.

list(APPEND compile_options "-fno-math-errno")
endif()
elseif(MSVC)
if(ADD_FMA_FLAG)
list(APPEND compile_options "/arch:AVX2")
Expand Down
5 changes: 0 additions & 5 deletions libc/cmake/modules/LLVMLibCTestRules.cmake
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@@ -1,11 +1,6 @@
function(_get_common_test_compile_options output_var c_test flags)
_get_compile_options_from_flags(compile_flags ${flags})

# Remove -fno-math-errno if it was added.
if(LIBC_ADD_FNO_MATH_ERRNO)
list(REMOVE_ITEM compile_options "-fno-math-errno")
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@lntue lntue Feb 5, 2025

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Are there tests failed because of this part? Last time I tried, there are failed math tests that check errno when the tests are built with -fno-math-errno.

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@petrhosek petrhosek Feb 5, 2025

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I don't see any test failures on the presubmit bots, should those exercise all tests?

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@lntue lntue Feb 5, 2025

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I mean the tests failed when the flag is set. I don't think any of our bots running baremetal config, so they don't cover this option.

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@petrhosek petrhosek Feb 6, 2025

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We don't currently run tests on baremetal so I don't know if we have any way to find out.

endif()

set(compile_options
${LIBC_COMPILE_OPTIONS_DEFAULT}
${LIBC_TEST_COMPILE_OPTIONS_DEFAULT}
Expand Down
2 changes: 1 addition & 1 deletion libc/config/baremetal/config.json
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@
},
"math": {
"LIBC_CONF_MATH_OPTIMIZATIONS": {
"value": "(LIBC_MATH_SKIP_ACCURATE_PASS | LIBC_MATH_SMALL_TABLES)"
"value": "(LIBC_MATH_SKIP_ACCURATE_PASS | LIBC_MATH_SMALL_TABLES | LIBC_MATH_NO_ERRNO)"
}
}
}