Reland "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

src/objects.h

 // Copyright 2012 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/base/bits.h"
@@ skipping 9154 matching lines @@
                           int from,
                           int to);
 
   // The return value may point to the first aligned word containing the first
   // non-one-byte character, rather than directly to the non-one-byte character.
   // If the return value is >= the passed length, the entire string was
   // one-byte.
   static inline int NonAsciiStart(const char* chars, int length) {
     const char* start = chars;
     const char* limit = chars + length;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-    DCHECK(unibrow::Utf8::kMaxOneByteChar == 0x7F);
-    const uintptr_t non_one_byte_mask = kUintptrAllBitsSet / 0xFF * 0x80;
-    while (chars + sizeof(uintptr_t) <= limit) {
-      if (*reinterpret_cast<const uintptr_t*>(chars) & non_one_byte_mask) {
-        return static_cast<int>(chars - start);
+
+    if (length >= kIntptrSize) {
+      // Check unaligned bytes.
+      while (!IsAligned(reinterpret_cast<intptr_t>(chars), sizeof(uintptr_t))) {
+        if (static_cast<uint8_t>(*chars) > unibrow::Utf8::kMaxOneByteChar) {
+          return static_cast<int>(chars - start);
+        }
+        ++chars;
       }
-      chars += sizeof(uintptr_t);
+      // Check aligned words.
+      DCHECK(unibrow::Utf8::kMaxOneByteChar == 0x7F);
+      const uintptr_t non_one_byte_mask = kUintptrAllBitsSet / 0xFF * 0x80;
+      while (chars + sizeof(uintptr_t) <= limit) {
+        if (*reinterpret_cast<const uintptr_t*>(chars) & non_one_byte_mask) {
+          return static_cast<int>(chars - start);
+        }
+        chars += sizeof(uintptr_t);
+      }
     }
-#endif
+    // Check remaining unaligned bytes.
     while (chars < limit) {
       if (static_cast<uint8_t>(*chars) > unibrow::Utf8::kMaxOneByteChar) {
         return static_cast<int>(chars - start);
       }
       ++chars;
     }
+
     return static_cast<int>(chars - start);
   }
 
   static inline bool IsAscii(const char* chars, int length) {
     return NonAsciiStart(chars, length) >= length;
   }
 
   static inline bool IsAscii(const uint8_t* chars, int length) {
     return
         NonAsciiStart(reinterpret_cast<const char*>(chars), length) >= length;
@@ skipping 1923 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_