1 files changed, 294 insertions, 0 deletions
diff --git a/mozglue/misc/SIMD_avx2.cpp b/mozglue/misc/SIMD_avx2.cpp
new file mode 100644
index 0000000000..a1467c7a55
--- /dev/null
+++ b/mozglue/misc/SIMD_avx2.cpp
@@ -0,0 +1,294 @@
+/* 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
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#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