Avoid decoding overhead when allocating ascii strings....

src/heap-inl.h

Index: src/heap-inl.h
===================================================================
--- src/heap-inl.h	(revision 6096)
+++ src/heap-inl.h	(working copy)
@@ -40,6 +40,21 @@
 }
 
 
+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) {