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x86-64: Require BMI2 for AVX2 strncmp implementation

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The AVX2 strncmp implementations uses the 'bzhi' instruction, which
belongs to the BMI2 CPU feature.

NB: It also uses the 'tzcnt' BMI1 instruction, but it is executed as BSF
as BSF if the CPU doesn't support TZCNT, and produces the same result
for non-zero input.

Partially fixes: b77b06e0e2 ("x86: Optimize strcmp-avx2.S")
Partially resolves: BZ #29611

Reviewed-by: Noah Goldstein  <goldstein.w.n@gmail.com>
This commit is contained in:
Aurelien Jarno 2022-10-03 23:46:11 +02:00
parent 4d64c64457
commit fc7de1d9b9
2 changed files with 7 additions and 4 deletions
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7
sysdeps/x86_64/multiarch/ifunc-impl-list.c
View File

@ -1176,13 +1176,16 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
IFUNC_IMPL (i, name, strncmp,
X86_IFUNC_IMPL_ADD_V4 (array, i, strncmp,
(CPU_FEATURE_USABLE (AVX512VL)
&& CPU_FEATURE_USABLE (AVX512BW)),
&& CPU_FEATURE_USABLE (AVX512BW)
&& CPU_FEATURE_USABLE (BMI2)),
__strncmp_evex)
X86_IFUNC_IMPL_ADD_V3 (array, i, strncmp,
CPU_FEATURE_USABLE (AVX2),
(CPU_FEATURE_USABLE (AVX2)
&& CPU_FEATURE_USABLE (BMI2)),
__strncmp_avx2)
X86_IFUNC_IMPL_ADD_V3 (array, i, strncmp,
(CPU_FEATURE_USABLE (AVX2)
&& CPU_FEATURE_USABLE (BMI2)
&& CPU_FEATURE_USABLE (RTM)),
__strncmp_avx2_rtm)
X86_IFUNC_IMPL_ADD_V2 (array, i, strncmp,

4
sysdeps/x86_64/multiarch/strncmp.c
View File

@ -41,12 +41,12 @@ IFUNC_SELECTOR (void)
const struct cpu_features *cpu_features = __get_cpu_features ();
if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2)
&& X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
AVX_Fast_Unaligned_Load, ))
{
if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
return OPTIMIZE (evex);
if (CPU_FEATURE_USABLE_P (cpu_features, RTM))