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Don't try to use AVX512 without OS support #566

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Don't try to use AVX512 without OS support #566

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6 changes: 5 additions & 1 deletion cbits/measure_off.c
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Original file line number Diff line number Diff line change
Expand Up @@ -44,12 +44,16 @@
bool has_avx512_vl_bw() {
#if (__GNUC__ >= 7 || __GNUC__ == 6 && __GNUC_MINOR__ >= 3) || defined(__clang_major__)
uint32_t eax = 0, ebx = 0, ecx = 0, edx = 0;
uint64_t xcr0;
__get_cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
// https://en.wikipedia.org/wiki/CPUID#EAX=7,_ECX=0:_Extended_Features
__asm__("xgetbv\n\t" : "=a" (xcr0) : "c" (0));
const bool has_avx512_bw = ebx & (1 << 30);
const bool has_avx512_vl = ebx & (1 << 31);
// XCR0 bits 5, 6, and 7
const bool avx512_os_enabled = (xcr0 & 0xE0) == 0xE0;
// printf("cpuid=%d=cpuid\n", has_avx512_bw && has_avx512_vl);
return has_avx512_bw && has_avx512_vl;
return has_avx512_bw && has_avx512_vl && avx512_os_enabled;
#else
return false;
#endif
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