x86-64: Require BMI2 for AVX2 strcmp implementation
The AVX2 strcmp implementation 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>
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@ -591,10 +591,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
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&& CPU_FEATURE_USABLE (BMI2)),
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__strcmp_evex)
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X86_IFUNC_IMPL_ADD_V3 (array, i, strcmp,
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CPU_FEATURE_USABLE (AVX2),
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(CPU_FEATURE_USABLE (AVX2)
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&& CPU_FEATURE_USABLE (BMI2)),
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__strcmp_avx2)
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X86_IFUNC_IMPL_ADD_V3 (array, i, strcmp,
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(CPU_FEATURE_USABLE (AVX2)
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&& CPU_FEATURE_USABLE (BMI2)
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&& CPU_FEATURE_USABLE (RTM)),
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__strcmp_avx2_rtm)
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X86_IFUNC_IMPL_ADD_V2 (array, i, strcmp,
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@ -45,12 +45,12 @@ IFUNC_SELECTOR (void)
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const struct cpu_features *cpu_features = __get_cpu_features ();
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if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
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&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2)
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&& X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
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AVX_Fast_Unaligned_Load, ))
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{
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if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
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&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
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&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
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&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
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return OPTIMIZE (evex);
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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