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[Support/BLAKE3] Make g_cpu_features thread safe #147948

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[Support/BLAKE3] Make g_cpu_features thread safe #147948

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ba1c486
[Support/BLAKE3] Make g_cpu_features thread safe
slydiman Jun 27, 2025
454f20d
[Support/BLAKE3] Make g_cpu_features thread safe
slydiman Jul 10, 2025
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48 changes: 40 additions & 8 deletions llvm/lib/Support/BLAKE3/blake3_dispatch.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,16 +4,46 @@

#include "blake3_impl.h"

#if defined(_MSC_VER)
#include <Windows.h>
#endif

#if defined(IS_X86)
#if defined(_MSC_VER)
#include <intrin.h>
#elif defined(__GNUC__)
#include <immintrin.h>
#else
#error "Unimplemented!"
#undef IS_X86 /* Unimplemented! */
#endif
#endif

#if !defined(BLAKE3_ATOMICS)
#if defined(__has_include)
#if __has_include(<stdatomic.h>) && !defined(_MSC_VER)
#define BLAKE3_ATOMICS 1
#else
#define BLAKE3_ATOMICS 0
#endif /* __has_include(<stdatomic.h>) && !defined(_MSC_VER) */
#else
#define BLAKE3_ATOMICS 0
#endif /* defined(__has_include) */
#endif /* BLAKE3_ATOMICS */

#if BLAKE3_ATOMICS
#define ATOMIC_INT _Atomic int
#define ATOMIC_LOAD(x) x
#define ATOMIC_STORE(x, y) x = y
#elif defined(_MSC_VER)
#define ATOMIC_INT LONG
#define ATOMIC_LOAD(x) InterlockedOr(&x, 0)
#define ATOMIC_STORE(x, y) InterlockedExchange(&x, y)
#else
#define ATOMIC_INT int
#define ATOMIC_LOAD(x) x
#define ATOMIC_STORE(x, y) x = y
#endif

#define MAYBE_UNUSED(x) (void)((x))

#if defined(IS_X86)
Expand Down Expand Up @@ -59,7 +89,6 @@ static void cpuidex(uint32_t out[4], uint32_t id, uint32_t sid) {
#endif
}

#endif

enum cpu_feature {
SSE2 = 1 << 0,
Expand All @@ -76,7 +105,7 @@ enum cpu_feature {
#if !defined(BLAKE3_TESTING)
static /* Allow the variable to be controlled manually for testing */
#endif
enum cpu_feature g_cpu_features = UNDEFINED;
ATOMIC_INT g_cpu_features = UNDEFINED;

LLVM_ATTRIBUTE_USED
#if !defined(BLAKE3_TESTING)
Expand All @@ -85,14 +114,16 @@ static
enum cpu_feature
get_cpu_features(void) {

if (g_cpu_features != UNDEFINED) {
return g_cpu_features;
/* If TSAN detects a data race here, try compiling with -DBLAKE3_ATOMICS=1 */
enum cpu_feature features = ATOMIC_LOAD(g_cpu_features);
if (features != UNDEFINED) {
return features;
} else {
#if defined(IS_X86)
uint32_t regs[4] = {0};
uint32_t *eax = &regs[0], *ebx = &regs[1], *ecx = &regs[2], *edx = &regs[3];
(void)edx;
enum cpu_feature features = 0;
features = 0;
cpuid(regs, 0);
const int max_id = *eax;
cpuid(regs, 1);
Expand All @@ -102,7 +133,7 @@ static
if (*edx & (1UL << 26))
features |= SSE2;
#endif
if (*ecx & (1UL << 0))
if (*ecx & (1UL << 9))
features |= SSSE3;
if (*ecx & (1UL << 19))
features |= SSE41;
Expand All @@ -125,14 +156,15 @@ static
}
}
}
g_cpu_features = features;
ATOMIC_STORE(g_cpu_features, features);
return features;
#else
/* How to detect NEON? */
return 0;
#endif
}
}
#endif

void blake3_compress_in_place(uint32_t cv[8],
const uint8_t block[BLAKE3_BLOCK_LEN],
Expand Down