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

[Aurelien Jarno <aurelien@aurel32.net>]

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
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