1 files changed, 9 insertions, 14 deletions
diff --git a/absl/hash/internal/low_level_hash.cc b/absl/hash/internal/low_level_hash.cc
index 6f9cb9c7..b5db0b89 100644
--- a/absl/hash/internal/low_level_hash.cc
+++ b/absl/hash/internal/low_level_hash.cc
@@ -15,7 +15,7 @@
 #include "absl/hash/internal/low_level_hash.h"
 
 #include "absl/base/internal/unaligned_access.h"
-#include "absl/numeric/bits.h"
+#include "absl/base/prefetch.h"
 #include "absl/numeric/int128.h"
 
 namespace absl {
@@ -23,24 +23,15 @@ ABSL_NAMESPACE_BEGIN
 namespace hash_internal {
 
 static uint64_t Mix(uint64_t v0, uint64_t v1) {
-#if !defined(__aarch64__)
-  // The default bit-mixer uses 64x64->128-bit multiplication.
   absl::uint128 p = v0;
   p *= v1;
   return absl::Uint128Low64(p) ^ absl::Uint128High64(p);
-#else
-  // The default bit-mixer above would perform poorly on some ARM microarchs,
-  // where calculating a 128-bit product requires a sequence of two
-  // instructions with a high combined latency and poor throughput.
-  // Instead, we mix bits using only 64-bit arithmetic, which is faster.
-  uint64_t p = v0 ^ absl::rotl(v1, 40);
-  p *= v1 ^ absl::rotl(v0, 39);
-  return p ^ (p >> 11);
-#endif
 }
 
 uint64_t LowLevelHash(const void* data, size_t len, uint64_t seed,
-                      const uint64_t salt[]) {
+                      const uint64_t salt[5]) {
+  // Prefetch the cacheline that data resides in.
+  PrefetchToLocalCache(data);
   const uint8_t* ptr = static_cast<const uint8_t*>(data);
   uint64_t starting_length = static_cast<uint64_t>(len);
   uint64_t current_state = seed ^ salt[0];
@@ -52,6 +43,9 @@ uint64_t LowLevelHash(const void* data, size_t len, uint64_t seed,
     uint64_t duplicated_state = current_state;
 
     do {
+      // Always prefetch the next cacheline.
+      PrefetchToLocalCache(ptr + ABSL_CACHELINE_SIZE);
+
       uint64_t a = absl::base_internal::UnalignedLoad64(ptr);
       uint64_t b = absl::base_internal::UnalignedLoad64(ptr + 8);
       uint64_t c = absl::base_internal::UnalignedLoad64(ptr + 16);
@@ -106,7 +100,8 @@ uint64_t LowLevelHash(const void* data, size_t len, uint64_t seed,
   } else if (len > 0) {
     // If we have at least 1 and at most 3 bytes, read all of the provided
     // bits into A, with some adjustments.
-    a = ((ptr[0] << 16) | (ptr[len >> 1] << 8) | ptr[len - 1]);
+    a = static_cast<uint64_t>((ptr[0] << 16) | (ptr[len >> 1] << 8) |
+                              ptr[len - 1]);
     b = 0;
   } else {
     a = 0;