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x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP
1. Set Prefer_No_VZEROUPPER if RTM is usable to avoid RTM abort triggered by VZEROUPPER inside a transactionally executing RTM region. 2. Since to compare 2 32-byte strings, 256-bit EVEX strcmp requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB, AVX2 strcmp is faster than EVEX strcmp. Add Prefer_AVX2_STRCMP to prefer AVX2 strcmp family functions.
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@ -531,8 +531,24 @@ init_cpu_features (struct cpu_features *cpu_features)
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cpu_features->preferred[index_arch_Prefer_No_VZEROUPPER]
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|= bit_arch_Prefer_No_VZEROUPPER;
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else
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cpu_features->preferred[index_arch_Prefer_No_AVX512]
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|= bit_arch_Prefer_No_AVX512;
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{
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cpu_features->preferred[index_arch_Prefer_No_AVX512]
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|= bit_arch_Prefer_No_AVX512;
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/* Avoid RTM abort triggered by VZEROUPPER inside a
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transactionally executing RTM region. */
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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cpu_features->preferred[index_arch_Prefer_No_VZEROUPPER]
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|= bit_arch_Prefer_No_VZEROUPPER;
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/* Since to compare 2 32-byte strings, 256-bit EVEX strcmp
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requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp
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requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB,
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AVX2 strcmp is faster than EVEX strcmp. */
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if (CPU_FEATURE_USABLE_P (cpu_features, AVX2))
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cpu_features->preferred[index_arch_Prefer_AVX2_STRCMP]
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|= bit_arch_Prefer_AVX2_STRCMP;
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}
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}
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/* This spells out "AuthenticAMD" or "HygonGenuine". */
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else if ((ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65)
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@ -239,6 +239,8 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
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CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
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Fast_Copy_Backward,
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disable, 18);
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CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
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(n, cpu_features, Prefer_AVX2_STRCMP, AVX2, disable, 18);
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}
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break;
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case 19:
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@ -32,3 +32,4 @@ BIT (Prefer_ERMS)
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BIT (Prefer_No_AVX512)
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BIT (MathVec_Prefer_No_AVX512)
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BIT (Prefer_FSRM)
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BIT (Prefer_AVX2_STRCMP)
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