Fast path for string.replace that replaces a single character by a string.

BUG=
TEST=

Review URL: http://codereview.chromium.org/9213002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -3011,7 +3011,7 @@ MaybeObject* Heap::AllocateSubString(String* buffer,
                                      int end,
                                      PretenureFlag pretenure) {
   int length = end - start;
-  if (length == 0) {
+  if (length <= 0) {
     return empty_string();
   } else if (length == 1) {
     return LookupSingleCharacterStringFromCode(buffer->Get(start));

src/runtime.cc

@@ -3233,6 +3233,59 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_StringReplaceRegExpWithString) {
 }
 
 
+Handle<String> Runtime::StringReplaceOneCharWithString(Isolate* isolate,
+                                                       Handle<String> subject,
+                                                       Handle<String> search,
+                                                       Handle<String> replace,
+                                                       bool* found) {
+  if (subject->IsConsString()) {
+    ConsString* cons = ConsString::cast(*subject);
+    Handle<String> first = Handle<String>(cons->first());
+    Handle<String> second = Handle<String>(cons->second());
+    Handle<String> new_first = StringReplaceOneCharWithString(isolate,
+                                                              first,
+                                                              search,
+                                                              replace,
+                                                              found);
+    if (*found) {
+      return isolate->factory()->NewConsString(new_first, second);
+    } else {
+      Handle<String> new_second = StringReplaceOneCharWithString(isolate,
+                                                                 second,
+                                                                 search,
+                                                                 replace,
+                                                                 found);
+      return isolate->factory()->NewConsString(first, new_second);
+    }
+  } else {
+    int index = StringMatch(isolate, subject, search, 0);
+    if (index == -1) return subject;
+    *found = true;
+    Handle<String> first = isolate->factory()->NewSubString(subject, 0, index);
+    Handle<String> cons1 = isolate->factory()->NewConsString(first, replace);
+    Handle<String> second =
+        isolate->factory()->NewSubString(subject, index + 1, subject->length());
+    return isolate->factory()->NewConsString(cons1, second);
+  }
+}
+
+
+RUNTIME_FUNCTION(MaybeObject*, Runtime_StringReplaceOneCharWithString) {
+  ASSERT(args.length() == 3);
+  HandleScope scope(isolate);
+  CONVERT_ARG_CHECKED(String, subject, 0);
+  CONVERT_ARG_CHECKED(String, search, 1);
+  CONVERT_ARG_CHECKED(String, replace, 2);
+  bool found = false;
+
+  return *(Runtime::StringReplaceOneCharWithString(isolate,
+                                                   subject,
+                                                   search,
+                                                   replace,
+                                                   &found));
+}
+
+
 // Perform string match of pattern on subject, starting at start index.
 // Caller must ensure that 0 <= start_index <= sub->length(),
 // and should check that pat->length() + start_index <= sub->length().

src/runtime.h

@@ -197,6 +197,7 @@ namespace internal {
   F(StringLocaleCompare, 2, 1) \
   F(SubString, 3, 1) \
   F(StringReplaceRegExpWithString, 4, 1) \
+  F(StringReplaceOneCharWithString, 3, 1) \
   F(StringMatch, 3, 1) \
   F(StringTrim, 3, 1) \
   F(StringToArray, 2, 1) \
@@ -629,6 +630,12 @@ class Runtime : public AllStatic {
   // Get the intrinsic function with the given FunctionId.
   static const Function* FunctionForId(FunctionId id);
 
+  static Handle<String> StringReplaceOneCharWithString(Isolate* isolate,
+                                                       Handle<String> subject,
+                                                       Handle<String> search,
+                                                       Handle<String> replace,
+                                                       bool* found);
+
   // General-purpose helper functions for runtime system.
   static int StringMatch(Isolate* isolate,
                          Handle<String> sub,

src/string.js

@@ -244,6 +244,11 @@ function StringReplace(search, replace) {
 
   // Convert the search argument to a string and search for it.
   search = TO_STRING_INLINE(search);
+  if (search.length == 1 &&
+      IS_STRING(replace) &&
+      %StringIndexOf(replace, '$', 0) < 0) {
+    return %StringReplaceOneCharWithString(subject, search, replace);
+  }
   var start = %StringIndexOf(subject, search, 0);
   if (start < 0) return subject;
   var end = start + search.length;