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x86: improve SIMD detection #257

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x86: improve SIMD detection #257

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15 changes: 10 additions & 5 deletions sljit_src/sljitNativeX86_common.c
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Original file line number Diff line number Diff line change
Expand Up @@ -572,12 +572,13 @@ static void get_cpu_features(void)
feature_list |= CPU_FEATURE_OSXSAVE;
if (info[2] & 0x10000000)
feature_list |= CPU_FEATURE_AVX;
#if (defined SLJIT_DETECT_SSE2 && SLJIT_DETECT_SSE2)
if (info[3] & 0x4000000)
feature_list |= CPU_FEATURE_SSE2;
#endif
if (info[3] & 0x8000)
feature_list |= CPU_FEATURE_CMOV;
#if (defined(SLJIT_DETECT_SSE2) && SLJIT_DETECT_SSE2) \
&& (defined(__SSE2__) || (defined(_WIN64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2)))
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This will disable SSE2 with SUNPRO, TINYC or other compilers than won't provide the defines.

if ((info[3] & 0x5000000) == 0x5000000)
feature_list |= CPU_FEATURE_SSE2;
#endif
}

info[0] = 0x80000000;
Expand All @@ -592,7 +593,11 @@ static void get_cpu_features(void)
feature_list |= CPU_FEATURE_LZCNT;
}

if ((feature_list & CPU_FEATURE_OSXSAVE) && (execute_get_xcr0_low() & 0x4) == 0)
#if defined(SLJIT_CONFIG_X86_32) && SLJIT_CONFIG_X86_32
if (!(feature_list & CPU_FEATURE_SSE2))
feature_list &= ~(sljit_u32)CPU_FEATURE_SSE41;
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Who sets this? Does the compiler runs on that old hardware?

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@carenas carenas Jul 5, 2024 •
edited
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Just like AVX2; SSE2 also needs OS support, which could be missing (ex: Debian 3).

When gcc targets a CPU with SSE2 it defines __SSE2__ just like MSVC does with _M_IX86_FP

Note that in this case, if saving of the XMM registers is not supported, any operation that uses them will SIGILL, hence why this code disables SSE41 (hence SIMD) in that case.

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The question was how is it possible to set SSE4.1 without setting SSE2. I always worry that we accidentally disables features for newer systems.

#endif
if (!(feature_list & CPU_FEATURE_OSXSAVE) || (execute_get_xcr0_low() & 0x4) == 0)
feature_list &= ~(sljit_u32)(CPU_FEATURE_AVX | CPU_FEATURE_AVX2);

cpu_feature_list = feature_list;
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