Reland "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

src/runtime.cc

 // 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.
 
 #include <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 6534 matching lines @@
   DisallowHeapAllocation no_gc;
   // We rely on the distance between upper and lower case letters
   // being a known power of 2.
   DCHECK('a' - 'A' == (1 << 5));
   // Boundaries for the range of input characters than require conversion.
   static const char lo = Converter::kIsToLower ? 'A' - 1 : 'a' - 1;
   static const char hi = Converter::kIsToLower ? 'Z' + 1 : 'z' + 1;
   bool changed = false;
   uintptr_t or_acc = 0;
   const char* const limit = src + length;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-  // Process the prefix of the input that requires no conversion one
-  // (machine) word at a time.
-  while (src <= limit - sizeof(uintptr_t)) {
-    const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
-    or_acc |= w;
-    if (AsciiRangeMask(w, lo, hi) != 0) {
-      changed = true;
-      break;
+
+  // dst is newly allocated and always aligned.
+  DCHECK(IsAligned(reinterpret_cast<intptr_t>(dst), sizeof(uintptr_t)));
+  // Only attempt processing one word at a time if src is also aligned.
+  if (IsAligned(reinterpret_cast<intptr_t>(src), sizeof(uintptr_t))) {
+    // Process the prefix of the input that requires no conversion one aligned
+    // (machine) word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      if (AsciiRangeMask(w, lo, hi) != 0) {
+        changed = true;
+        break;
+      }
+      *reinterpret_cast<uintptr_t*>(dst) = w;
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
     }
-    *reinterpret_cast<uintptr_t*>(dst) = w;
-    src += sizeof(uintptr_t);
-    dst += sizeof(uintptr_t);
+    // Process the remainder of the input performing conversion when
+    // required one word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      uintptr_t m = AsciiRangeMask(w, lo, hi);
+      // The mask has high (7th) bit set in every byte that needs
+      // conversion and we know that the distance between cases is
+      // 1 << 5.
+      *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
+    }
   }
-  // Process the remainder of the input performing conversion when
-  // required one word at a time.
-  while (src <= limit - sizeof(uintptr_t)) {
-    const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
-    or_acc |= w;
-    uintptr_t m = AsciiRangeMask(w, lo, hi);
-    // The mask has high (7th) bit set in every byte that needs
-    // conversion and we know that the distance between cases is
-    // 1 << 5.
-    *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
-    src += sizeof(uintptr_t);
-    dst += sizeof(uintptr_t);
-  }
-#endif
   // Process the last few bytes of the input (or the whole input if
   // unaligned access is not supported).
   while (src < limit) {
     char c = *src;
     or_acc |= c;
     if (lo < c && c < hi) {
       c ^= (1 << 5);
       changed = true;
     }
     *dst = c;
     ++src;
     ++dst;
   }
-  if ((or_acc & kAsciiMask) != 0) {
-    return false;
-  }
+
+  if ((or_acc & kAsciiMask) != 0) return false;
 
   DCHECK(CheckFastAsciiConvert(
              saved_dst, saved_src, length, changed, Converter::kIsToLower));
 
   *changed_out = changed;
   return true;
 }
 
 }  // namespace
 
@@ skipping 9069 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal