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[libc] Skip x87 floating point register and only update mxcsr for x86_64 targets when raising exceptions inside math functions. (#144951)

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Updating x87 floating point register significantly affect the
performance of the functions.
All the floating point exception reads will merge the results from both
mxcsr and x87 registers anyway.
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lntue 2025-06-19 17:06:52 -04:00 committed by GitHub
parent 53336ad488
commit 2f3a8fd0b3
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GPG Key ID: B5690EEEBB952194
2 changed files with 13 additions and 5 deletions
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5
libc/src/__support/FPUtil/FEnvImpl.h
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@ -91,7 +91,12 @@ LIBC_INLINE static int set_except_if_required([[maybe_unused]] int excepts) {
LIBC_INLINE static int raise_except_if_required([[maybe_unused]] int excepts) {
#ifndef LIBC_MATH_HAS_NO_EXCEPT
if (math_errhandling & MATH_ERREXCEPT)
#ifdef LIBC_TARGET_ARCH_IS_X86_64
return raise_except</*SKIP_X87_FPU*/ true>(excepts);
#else // !LIBC_TARGET_ARCH_IS_X86
return raise_except(excepts);
#endif // LIBC_TARGET_ARCH_IS_X86
#endif // LIBC_MATH_HAS_NO_EXCEPT
return 0;
}

13
libc/src/__support/FPUtil/x86_64/FEnvImpl.h
View File

@ -239,7 +239,7 @@ LIBC_INLINE int set_except(int excepts) {
return 0;
}
LIBC_INLINE int raise_except(int excepts) {
template <bool SKIP_X87_FPU = false> LIBC_INLINE int raise_except(int excepts) {
uint16_t status_value = internal::get_status_value_for_except(excepts);
// We set the status flag for exception one at a time and call the
@ -256,13 +256,16 @@ LIBC_INLINE int raise_except(int excepts) {
// when raising the next exception.
auto raise_helper = [](uint16_t singleExceptFlag) {
internal::X87StateDescriptor state;
if constexpr (!SKIP_X87_FPU) {
internal::X87StateDescriptor state;
internal::get_x87_state_descriptor(state);
state.status_word |= singleExceptFlag;
internal::write_x87_state_descriptor(state);
}
uint32_t mxcsr = 0;
internal::get_x87_state_descriptor(state);
mxcsr = internal::get_mxcsr();
state.status_word |= singleExceptFlag;
mxcsr |= singleExceptFlag;
internal::write_x87_state_descriptor(state);
internal::write_mxcsr(mxcsr);
internal::fwait();
};