diff options
| author | H.J. Lu <hjl.tools@gmail.com> | 2019-07-24 14:48:33 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2019-07-24 14:48:43 -0700 |
| commit | 7e681561a3aea7aa8f21fb031a7c778147dfdf5b (patch) | |
| tree | 9d70b934aeae381ec82fa7b21481728bbf0ad59a /sysdeps/x86_64/fpu | |
| parent | 82c664ed751f52a3074a9d6d366e87086f10b2f4 (diff) | |
| download | glibc-7e681561a3aea7aa8f21fb031a7c778147dfdf5b.zip glibc-7e681561a3aea7aa8f21fb031a7c778147dfdf5b.tar.gz glibc-7e681561a3aea7aa8f21fb031a7c778147dfdf5b.tar.bz2 | |
x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]
When compiled with -O3 and AVX, GCC 8 and 9 optimize some loops in
sysdeps/ieee754/dbl-64/branred.c with 256-bit vector instructions,
which leads to store forward stall:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90579
There is no easy fix in compiler. This patch limits vector width to
128 bits to work around this issue. It improves performance of sin
and cos by more than 40% on Skylake compiled with -O3 -march=skylake.
Tested with GCC 7/8/9 on x86-64.
[BZ #24603]
* sysdeps/x86_64/configure.ac: Check if -mprefer-vector-width=128
works.
* sysdeps/x86_64/configure: Regenerated.
* sysdeps/x86_64/fpu/Makefile (CFLAGS-branred.c): New. Set
to -mprefer-vector-width=128 if supported.
Diffstat (limited to 'sysdeps/x86_64/fpu')
| -rw-r--r-- | sysdeps/x86_64/fpu/Makefile | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/sysdeps/x86_64/fpu/Makefile b/sysdeps/x86_64/fpu/Makefile index 2b7d69b..74b14ba 100644 --- a/sysdeps/x86_64/fpu/Makefile +++ b/sysdeps/x86_64/fpu/Makefile @@ -237,3 +237,15 @@ CFLAGS-test-float-libmvec-sincosf-avx512.c = -DREQUIRE_AVX512F CFLAGS-test-float-libmvec-sincosf-avx512-main.c = $(libmvec-sincos-cflags) $(float-vlen16-arch-ext-cflags) endif endif + +ifeq ($(subdir)$(config-cflags-mprefer-vector-width),mathyes) +# When compiled with -O3 -march=skylake, GCC 8 and 9 optimize some loops +# in branred.c with 256-bit vector instructions, which leads to store +# forward stall: +# +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90579 +# +# Limit vector width to 128 bits to work around this issue. It improves +# performance of sin and cos by more than 40% on Skylake. +CFLAGS-branred.c = -mprefer-vector-width=128 +endif |