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Bug 1792158 - Restrict SIMD_avx2 to AMD64 r=stransky

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Differential Revision: https://phabricator.services.mozilla.com/D158785
This commit is contained in:
Doug Thayer 2022-10-10 16:15:48 +00:00
parent 9b68d17dda
commit c73a559a01
2 changed files with 26 additions and 4 deletions
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25
mozglue/misc/SIMD.cpp
View File

@ -439,8 +439,27 @@ const char* SIMD::memchr8SSE2(const char* ptr, char value, size_t length) {
return reinterpret_cast<const char*>(uresult);
}
// So, this is a bit awkward. It generally simplifies things if we can just
// assume all the AVX2 code is 64-bit, so we have this preprocessor guard
// in SIMD_avx2 over all of its actual code, and it also defines versions
// of its endpoints that just assert false if the guard is not satisfied.
// A 32 bit processor could implement the AVX2 instruction set though, which
// would result in it passing the supports_avx2() check and landing in an
// assertion failure. Accordingly, we just don't allow that to happen. We
// are not particularly concerned about ensuring that newer 32 bit processors
// get access to the AVX2 functions exposed here.
# if defined(MOZILLA_MAY_SUPPORT_AVX2) && defined(__x86_64__)
bool SupportsAVX2() { return supports_avx2(); }
# else
bool SupportsAVX2() { return false; }
# endif
const char* SIMD::memchr8(const char* ptr, char value, size_t length) {
if (supports_avx2()) {
if (SupportsAVX2()) {
return memchr8AVX2(ptr, value, length);
}
return memchr8SSE2(ptr, value, length);
@ -453,7 +472,7 @@ const char16_t* SIMD::memchr16SSE2(const char16_t* ptr, char16_t value,
const char16_t* SIMD::memchr16(const char16_t* ptr, char16_t value,
size_t length) {
if (supports_avx2()) {
if (SupportsAVX2()) {
return memchr16AVX2(ptr, value, length);
}
return memchr16SSE2(ptr, value, length);
@ -461,7 +480,7 @@ const char16_t* SIMD::memchr16(const char16_t* ptr, char16_t value,
const uint64_t* SIMD::memchr64(const uint64_t* ptr, uint64_t value,
size_t length) {
if (supports_avx2()) {
if (SupportsAVX2()) {
return memchr64AVX2(ptr, value, length);
}
return FindInBufferNaive<uint64_t>(ptr, value, length);

5
mozglue/misc/SIMD_avx2.cpp
View File

@ -8,7 +8,10 @@
#include "mozilla/SSE.h"
#include "mozilla/Assertions.h"
#ifdef MOZILLA_MAY_SUPPORT_AVX2
// Restricting to x86_64 simplifies things, and we're not particularly
// worried about slightly degraded performance on 32 bit processors which
// support AVX2, as this should be quite a minority.
#if defined(MOZILLA_MAY_SUPPORT_AVX2) && defined(__x86_64__)
# include <cstring>
# include <immintrin.h>