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authorH.J. Lu <hjl.tools@gmail.com>2017-03-21 10:59:31 -0700
committerH.J. Lu <hjl.tools@gmail.com>2017-04-20 07:55:44 -0700
commit883cadc5543ffd3a4537498b44c782ded8a4a4e8 (patch)
tree7f8420bd13c9e7660a4e097c9f62b01a2695a2d2 /scripts/abilist.awk
parent83037ea1d9e84b1b44ed307f01cbb5eeac24e22d (diff)
downloadglibc-hjl/pr21258/2.23.tar.gz
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x86-64: Improve branch predication in _dl_runtime_resolve_avx512_opt [BZ #21258] hjl/pr21258/2.23
On Skylake server, _dl_runtime_resolve_avx512_opt is used to preserve
the first 8 vector registers.  The code layout is

  if only %xmm0 - %xmm7 registers are used
     preserve %xmm0 - %xmm7 registers
  if only %ymm0 - %ymm7 registers are used
     preserve %ymm0 - %ymm7 registers
  preserve %zmm0 - %zmm7 registers

Branch predication always executes the fallthrough code path to preserve
%zmm0 - %zmm7 registers speculatively, even though only %xmm0 - %xmm7
registers are used.  This leads to lower CPU frequency on Skylake
server.  This patch changes the fallthrough code path to preserve
%xmm0 - %xmm7 registers instead:

  if whole %zmm0 - %zmm7 registers are used
    preserve %zmm0 - %zmm7 registers
  if only %ymm0 - %ymm7 registers are used
     preserve %ymm0 - %ymm7 registers
  preserve %xmm0 - %xmm7 registers

Tested on Skylake server.

	[BZ #21258]
	* sysdeps/x86_64/dl-trampoline.S (_dl_runtime_resolve_opt):
	Define only if _dl_runtime_resolve is defined to
	_dl_runtime_resolve_sse_vex.
	* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve_opt):
	Fallthrough to _dl_runtime_resolve_sse_vex.

(cherry picked from commit c15f8eb50cea7ad1a4ccece6e0982bf426d52c00)
Diffstat (limited to 'scripts/abilist.awk')
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