Re: [PATCH v2 0/6] x86: Fix AVX2 string functions requiring BMI1, BMI2 or LZCNT (BZ #29611)

[Aurelien Jarno <aurelien@aurel32.net>]

On 2022-10-02 09:21, Noah Goldstein wrote:
> On Sun, Oct 2, 2022 at 5:34 AM Aurelien Jarno <aurelien@aurel32.net> wrote:
> >
> > Some early Intel Haswell CPU have AVX2 instructions, but do not have
> > BMI1 and BMI2 instructions. Some AVX2 string functions only check for
> > AVX2, but use BMI1, BMI2 or LZCNT instructions. This patchset tries to
> > fix that.
> >
> > While most fixes only change ifunc-impl-list.c, and thus only concerns
> > the testsuite, the strn(case)cmp is a real issue affecting early Intel
> 
> str(case)cmp as well, correct?

Oops, yes forgot to update the cover letter on that aspect.

> > Haswell CPU, reported to affect Debian Sid and Fedora Rawhide.
> >
> > On the other hand, the check for LZCNT in memrchr is purely for
> > correctness, I am not aware of a CPU implementing AVX2 without LZCNT.
> >
> > This has been tested by remplacing all BMI1 and BMI2 instructions in the
> > source code by the "ud2" instruction and disabling the BMI1, BMI2
> > feature detection, and running the testsuite.
> >
> > Resolves: BZ #29611
> >
> > Change v1 -> v2:
> > - Better scan for BMI2 instructions (shlx and shrx) and BMI1
> >   instructions (blsmsk) instructions following the feedback from Noah
> >   Goldstein
> >
> > Aurelien Jarno (6):
> >   x86: include BMI1 and BMI2 in x86-64-v3 level
> >   x86-64: Require BMI2 for AVX2 str*cmp and wcs(n)cmp implementations
> >   x86-64: Require BMI2 for AVX2 (raw|w)memchr implementations
> >   x86-64: Require LZCNT for AVX2 memrchr implementation
> >   x86-64: Require BMI1/BMI2 for AVX2 strrchr and wcsrchr implementations
> >   x86-64: Require BMI2 for AVX2 memrchr implementation
> >
> >  sysdeps/x86/get-isa-level.h                 |  2 +
> >  sysdeps/x86/isa-level.h                     |  2 +
> >  sysdeps/x86_64/multiarch/ifunc-avx2.h       |  2 +
> >  sysdeps/x86_64/multiarch/ifunc-impl-list.c  | 86 ++++++++++++++++-----
> >  sysdeps/x86_64/multiarch/ifunc-strcasecmp.h |  1 +
> >  sysdeps/x86_64/multiarch/strcmp.c           |  4 +-
> >  sysdeps/x86_64/multiarch/strncmp.c          |  4 +-
> >  7 files changed, 76 insertions(+), 25 deletions(-)
> >
> > --
> > 2.35.1
> >
> 

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net