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Fix sysdeps/x86/fpu/s_ffma.c for 32-bit FMA processor case

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It turns out the __SSE2_MATH__ conditional in sysdeps/x86/fpu/s_ffma.c
does not cover all cases where the x86 fenv_private.h macros might
manipulate one of the SSE and 387 floating-point state, while the
actual fma implementation uses the other.  Specifically, in the 32-bit
case, with a compiler not defaulting to -mfpmath=sse, but testing on a
processor with hardware FMA support, the multiarch fma function
implementations will end up using SSE, while the fenv_private.h macros
will use the 387 state for double.  Change the conditional to use the
default macros rather than the optimized ones in all cases except when
the compiler inlines an fma instruction (in which case, since all
those instructions are SSE instructions and -mfpmath=sse must be in
effect for them to be inlined, the optimized macros will only use the
SSE state and it's OK for them to only use the SSE state).

Tested for x86_64 and x86.  H.J. reports in
<https://sourceware.org/pipermail/libc-alpha/2021-September/131367.html>
that it fixes the problems he observed.
This commit is contained in:
Joseph Myers 2021-09-24 17:59:22 +00:00
parent 5ad9d62c3b
commit b26901b26e
1 changed files with 6 additions and 2 deletions
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8
sysdeps/x86/fpu/s_ffma.c
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@ -27,10 +27,14 @@
#include <math-narrow.h>
#if defined __SSE2_MATH__ && !defined __FP_FAST_FMA
#ifndef __FP_FAST_FMA
/* Depending on the details of the glibc configuration, fma might use
either SSE or 387 arithmetic; ensure that both parts of the
floating-point state are handled in the round-to-odd code. */
floating-point state are handled in the round-to-odd code. If
__FP_FAST_FMA is defined, that implies that the compiler is using
SSE floating point and that the fma call will be inlined, so the
x86 macros will work with only the SSE state and that is
sufficient. */
# undef libc_feholdexcept_setround
# define libc_feholdexcept_setround default_libc_feholdexcept_setround
# undef libc_feupdateenv_test