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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#include "mozilla/SIMD.h"
#include "mozilla/SSE.h"
#include "mozilla/Assertions.h"
// 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>
# include <stdint.h>
# include <type_traits>
# include "mozilla/EndianUtils.h"
namespace mozilla {
const __m256i* Cast256(uintptr_t ptr) {
return reinterpret_cast<const __m256i*>(ptr);
}
template <typename T>
T GetAs(uintptr_t ptr) {
return *reinterpret_cast<const T*>(ptr);
}
uintptr_t AlignDown32(uintptr_t ptr) { return ptr & ~0x1f; }
uintptr_t AlignUp32(uintptr_t ptr) { return AlignDown32(ptr + 0x1f); }
template <typename TValue>
__m128i CmpEq128(__m128i a, __m128i b) {
static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2);
if (sizeof(TValue) == 1) {
return _mm_cmpeq_epi8(a, b);
}
return _mm_cmpeq_epi16(a, b);
}
template <typename TValue>
__m256i CmpEq256(__m256i a, __m256i b) {
static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2 ||
sizeof(TValue) == 8);
if (sizeof(TValue) == 1) {
return _mm256_cmpeq_epi8(a, b);
}
if (sizeof(TValue) == 2) {
return _mm256_cmpeq_epi16(a, b);
}
return _mm256_cmpeq_epi64(a, b);
}
# if defined(__GNUC__) && !defined(__clang__)
// See the comment in SIMD.cpp over Load32BitsIntoXMM. This is just adapted
// from that workaround. Testing this, it also yields the correct instructions
// across all tested compilers.
__m128i Load64BitsIntoXMM(uintptr_t ptr) {
int64_t tmp;
memcpy(&tmp, reinterpret_cast<const void*>(ptr), sizeof(tmp));
return _mm_cvtsi64_si128(tmp);
}
# else
__m128i Load64BitsIntoXMM(uintptr_t ptr) {
return _mm_loadu_si64(reinterpret_cast<const __m128i*>(ptr));
}
# endif
template <typename TValue>
const TValue* Check4x8Bytes(__m128i needle, uintptr_t a, uintptr_t b,
uintptr_t c, uintptr_t d) {
__m128i haystackA = Load64BitsIntoXMM(a);
__m128i cmpA = CmpEq128<TValue>(needle, haystackA);
__m128i haystackB = Load64BitsIntoXMM(b);
__m128i cmpB = CmpEq128<TValue>(needle, haystackB);
__m128i haystackC = Load64BitsIntoXMM(c);
__m128i cmpC = CmpEq128<TValue>(needle, haystackC);
__m128i haystackD = Load64BitsIntoXMM(d);
__m128i cmpD = CmpEq128<TValue>(needle, haystackD);
__m128i or_ab = _mm_or_si128(cmpA, cmpB);
__m128i or_cd = _mm_or_si128(cmpC, cmpD);
__m128i or_abcd = _mm_or_si128(or_ab, or_cd);
int orMask = _mm_movemask_epi8(or_abcd);
if (orMask & 0xff) {
int cmpMask;
cmpMask = _mm_movemask_epi8(cmpA);
if (cmpMask & 0xff) {
return reinterpret_cast<const TValue*>(a + __builtin_ctz(cmpMask));
}
cmpMask = _mm_movemask_epi8(cmpB);
if (cmpMask & 0xff) {
return reinterpret_cast<const TValue*>(b + __builtin_ctz(cmpMask));
}
cmpMask = _mm_movemask_epi8(cmpC);
if (cmpMask & 0xff) {
return reinterpret_cast<const TValue*>(c + __builtin_ctz(cmpMask));
}
cmpMask = _mm_movemask_epi8(cmpD);
if (cmpMask & 0xff) {
return reinterpret_cast<const TValue*>(d + __builtin_ctz(cmpMask));
}
}
return nullptr;
}
template <typename TValue>
const TValue* Check4x32Bytes(__m256i needle, uintptr_t a, uintptr_t b,
uintptr_t c, uintptr_t d) {
__m256i haystackA = _mm256_loadu_si256(Cast256(a));
__m256i cmpA = CmpEq256<TValue>(needle, haystackA);
__m256i haystackB = _mm256_loadu_si256(Cast256(b));
__m256i cmpB = CmpEq256<TValue>(needle, haystackB);
__m256i haystackC = _mm256_loadu_si256(Cast256(c));
__m256i cmpC = CmpEq256<TValue>(needle, haystackC);
__m256i haystackD = _mm256_loadu_si256(Cast256(d));
__m256i cmpD = CmpEq256<TValue>(needle, haystackD);
__m256i or_ab = _mm256_or_si256(cmpA, cmpB);
__m256i or_cd = _mm256_or_si256(cmpC, cmpD);
__m256i or_abcd = _mm256_or_si256(or_ab, or_cd);
int orMask = _mm256_movemask_epi8(or_abcd);
if (orMask) {
int cmpMask;
cmpMask = _mm256_movemask_epi8(cmpA);
if (cmpMask) {
return reinterpret_cast<const TValue*>(a + __builtin_ctz(cmpMask));
}
cmpMask = _mm256_movemask_epi8(cmpB);
if (cmpMask) {
return reinterpret_cast<const TValue*>(b + __builtin_ctz(cmpMask));
}
cmpMask = _mm256_movemask_epi8(cmpC);
if (cmpMask) {
return reinterpret_cast<const TValue*>(c + __builtin_ctz(cmpMask));
}
cmpMask = _mm256_movemask_epi8(cmpD);
if (cmpMask) {
return reinterpret_cast<const TValue*>(d + __builtin_ctz(cmpMask));
}
}
return nullptr;
}
template <typename TValue>
const TValue* FindInBufferAVX2(const TValue* ptr, TValue value, size_t length) {
static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2 ||
sizeof(TValue) == 8);
static_assert(std::is_unsigned<TValue>::value);
// Load our needle into a 32-byte register
__m256i needle;
if (sizeof(TValue) == 1) {
needle = _mm256_set1_epi8(value);
} else if (sizeof(TValue) == 2) {
needle = _mm256_set1_epi16(value);
} else {
needle = _mm256_set1_epi64x(value);
}
size_t numBytes = length * sizeof(TValue);
uintptr_t cur = reinterpret_cast<uintptr_t>(ptr);
uintptr_t end = cur + numBytes;
if (numBytes < 8 || (sizeof(TValue) == 8 && numBytes < 32)) {
while (cur < end) {
if (GetAs<TValue>(cur) == value) {
return reinterpret_cast<const TValue*>(cur);
}
cur += sizeof(TValue);
}
return nullptr;
}
if constexpr (sizeof(TValue) != 8) {
if (numBytes < 32) {
__m128i needle_narrow;
if (sizeof(TValue) == 1) {
needle_narrow = _mm_set1_epi8(value);
} else {
needle_narrow = _mm_set1_epi16(value);
}
uintptr_t a = cur;
uintptr_t b = cur + ((numBytes & 16) >> 1);
uintptr_t c = end - 8 - ((numBytes & 16) >> 1);
uintptr_t d = end - 8;
return Check4x8Bytes<TValue>(needle_narrow, a, b, c, d);
}
}
if (numBytes < 128) {
// NOTE: here and below, we have some bit fiddling which could look a
// little weird. The important thing to note though is it's just a trick
// for getting the number 32 if numBytes is greater than or equal to 64,
// and 0 otherwise. This lets us fully cover the range without any
// branching for the case where numBytes is in [32,64), and [64,128). We get
// four ranges from this - if numbytes > 64, we get:
// [0,32), [32,64], [end - 64), [end - 32)
// and if numbytes < 64, we get
// [0,32), [0,32), [end - 32), [end - 32)
uintptr_t a = cur;
uintptr_t b = cur + ((numBytes & 64) >> 1);
uintptr_t c = end - 32 - ((numBytes & 64) >> 1);
uintptr_t d = end - 32;
return Check4x32Bytes<TValue>(needle, a, b, c, d);
}
// Get the initial unaligned load out of the way. This will overlap with the
// aligned stuff below, but the overlapped part should effectively be free
// (relative to a mispredict from doing a byte-by-byte loop).
__m256i haystack = _mm256_loadu_si256(Cast256(cur));
__m256i cmp = CmpEq256<TValue>(needle, haystack);
int cmpMask = _mm256_movemask_epi8(cmp);
if (cmpMask) {
return reinterpret_cast<const TValue*>(cur + __builtin_ctz(cmpMask));
}
// Now we're working with aligned memory. Hooray! \o/
cur = AlignUp32(cur);
uintptr_t tailStartPtr = AlignDown32(end - 96);
uintptr_t tailEndPtr = end - 32;
while (cur < tailStartPtr) {
uintptr_t a = cur;
uintptr_t b = cur + 32;
uintptr_t c = cur + 64;
uintptr_t d = cur + 96;
const TValue* result = Check4x32Bytes<TValue>(needle, a, b, c, d);
if (result) {
return result;
}
cur += 128;
}
uintptr_t a = tailStartPtr;
uintptr_t b = tailStartPtr + 32;
uintptr_t c = tailStartPtr + 64;
uintptr_t d = tailEndPtr;
return Check4x32Bytes<TValue>(needle, a, b, c, d);
}
const char* SIMD::memchr8AVX2(const char* ptr, char value, size_t length) {
const unsigned char* uptr = reinterpret_cast<const unsigned char*>(ptr);
unsigned char uvalue = static_cast<unsigned char>(value);
const unsigned char* uresult =
FindInBufferAVX2<unsigned char>(uptr, uvalue, length);
return reinterpret_cast<const char*>(uresult);
}
const char16_t* SIMD::memchr16AVX2(const char16_t* ptr, char16_t value,
size_t length) {
return FindInBufferAVX2<char16_t>(ptr, value, length);
}
const uint64_t* SIMD::memchr64AVX2(const uint64_t* ptr, uint64_t value,
size_t length) {
return FindInBufferAVX2<uint64_t>(ptr, value, length);
}
} // namespace mozilla
#else
namespace mozilla {
const char* SIMD::memchr8AVX2(const char* ptr, char value, size_t length) {
MOZ_RELEASE_ASSERT(false, "AVX2 not supported in this binary.");
}
const char16_t* SIMD::memchr16AVX2(const char16_t* ptr, char16_t value,
size_t length) {
MOZ_RELEASE_ASSERT(false, "AVX2 not supported in this binary.");
}
const uint64_t* SIMD::memchr64AVX2(const uint64_t* ptr, uint64_t value,
size_t length) {
MOZ_RELEASE_ASSERT(false, "AVX2 not supported in this binary.");
}
} // namespace mozilla
#endif