Revert "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/allocation-site-scopes.h"
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 8489 matching lines @@
   return array;
 }
 
 
 // Compares the contents of two strings by reading and comparing
 // int-sized blocks of characters.
 template <typename Char>
 static inline bool CompareRawStringContents(const Char* const a,
                                             const Char* const b,
                                             int length) {
-  return CompareChars(a, b, length) == 0;
+  int i = 0;
+#ifndef V8_HOST_CAN_READ_UNALIGNED
+  // If this architecture isn't comfortable reading unaligned ints
+  // then we have to check that the strings are aligned before
+  // comparing them blockwise.
+  const int kAlignmentMask = sizeof(uint32_t) - 1;  // NOLINT
+  uintptr_t pa_addr = reinterpret_cast<uintptr_t>(a);
+  uintptr_t pb_addr = reinterpret_cast<uintptr_t>(b);
+  if (((pa_addr & kAlignmentMask) | (pb_addr & kAlignmentMask)) == 0) {
+#endif
+    const int kStepSize = sizeof(int) / sizeof(Char);  // NOLINT
+    int endpoint = length - kStepSize;
+    // Compare blocks until we reach near the end of the string.
+    for (; i <= endpoint; i += kStepSize) {
+      uint32_t wa = *reinterpret_cast<const uint32_t*>(a + i);
+      uint32_t wb = *reinterpret_cast<const uint32_t*>(b + i);
+      if (wa != wb) {
+        return false;
+      }
+    }
+#ifndef V8_HOST_CAN_READ_UNALIGNED
+  }
+#endif
+  // Compare the remaining characters that didn't fit into a block.
+  for (; i < length; i++) {
+    if (a[i] != b[i]) {
+      return false;
+    }
+  }
+  return true;
 }
 
 
 template<typename Chars1, typename Chars2>
 class RawStringComparator : public AllStatic {
  public:
   static inline bool compare(const Chars1* a, const Chars2* b, int len) {
     DCHECK(sizeof(Chars1) != sizeof(Chars2));
     for (int i = 0; i < len; i++) {
       if (a[i] != b[i]) {
@@ skipping 7851 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal