Add a safe API for creating ASCII-only strings

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index dac28f34b22636ca359851615926a9e111bf258d..6dd83d422587ace5824f45db0fb96eab0e44909d 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -4534,6 +4534,28 @@ MaybeObject* Heap::AllocateStringFromOneByte(Vector<const char> string,
 }
 
 
+MaybeObject* Heap::AllocateStringFromAsciiSafe(Vector<const char> string,
+                                               PretenureFlag pretenure) {
+  if (string.length() == 1) {
+    return Heap::LookupSingleCharacterStringFromCode(string
+        [0] & String::kMaxAsciiCharCodeU);
+  }
+  Object* result;
+  { MaybeObject* maybe_result =
+        AllocateRawAsciiString(string.length(), pretenure);
+    if (!maybe_result->ToObject(&result)) return maybe_result;
+  }
+
+  // Copy the characters into the new object.
+  SeqAsciiString* string_result = SeqAsciiString::cast(result);
+  for (int i = 0; i < string.length(); i++) {
+    string_result->SeqAsciiStringSet(i,

[bnoordhuis1, 2012/12/07 04:54:47]

AllocateRawAsciiString and SeqAsciiString don't exist in HEAD.

+                                     string[i] & String::kMaxAsciiCharCodeU);
+  }
+  return result;
+}
+
+
 MaybeObject* Heap::AllocateStringFromUtf8Slow(Vector<const char> string,
                                               int non_ascii_start,
                                               PretenureFlag pretenure) {