Revert "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index ffe724f76376a911eaadda0064139f8381019667..f73d33f2a8edffb2e338bd956df8507e8dde9b34 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -8507,7 +8507,36 @@ 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;
 }