Avoid decoding overhead when allocating ascii strings....

src/heap-inl.h

 // Copyright 2006-2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 22 matching lines @@
 #include "v8-counters.h"
 
 namespace v8 {
 namespace internal {
 
 int Heap::MaxObjectSizeInPagedSpace() {
   return Page::kMaxHeapObjectSize;
 }
 
 
+MaybeObject* Heap::AllocateStringFromUtf8(Vector<const char> str,
+                                          PretenureFlag pretenure) {
+  // Check for ascii first since this is the common case.

[Lasse Reichstein, 2010/12/21 12:48:12]

ASCII is an acronym, even though we might not respect that in function names.
More instances below.

[Mads Ager (chromium), 2010/12/21 12:55:52]

Done.

+  for (int i = 0; i < str.length(); ++i) {
+    if (static_cast<uc16>(str[i]) > String::kMaxAsciiCharCode) {

[Lasse Reichstein, 2010/12/21 12:48:12]

Just cast to uint8_t, and compare to String:kMaxAsciiCharCodeU. It will allow
the compiler to just check the sign bit.

[Mads Ager (chromium), 2010/12/21 12:55:52]

Done.

+      // Non-ascii and we need to decode.
+      return AllocateStringFromUtf8Slow(str, pretenure);
+    }
+  }
+  // If the string is ascii, we do not need to convert the characters
+  // since UTF8 is backwards compatible with ascii.
+  return AllocateStringFromAscii(str, pretenure);
+}
+
+
 MaybeObject* Heap::AllocateSymbol(Vector<const char> str,
                                   int chars,
                                   uint32_t hash_field) {
   unibrow::Utf8InputBuffer<> buffer(str.start(),
                                     static_cast<unsigned>(str.length()));
   return AllocateInternalSymbol(&buffer, chars, hash_field);
 }
 
 
 MaybeObject* Heap::CopyFixedArray(FixedArray* src) {
@@ skipping 447 matching lines @@
 
 
 void ExternalStringTable::ShrinkNewStrings(int position) {
   new_space_strings_.Rewind(position);
   Verify();
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_INL_H_