From abbc6b9147e1e56ec182420ff18da02371fb7177 Mon Sep 17 00:00:00 2001
From: "sgjesse@chromium.org"
 <sgjesse@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 28 Oct 2009 09:11:45 +0000
Subject: [PATCH] Don't use string slices when processing RexExp replace.

String slices from RegExp replace results is now encoded in either one or two smis. Substrings are not used any more.

If the existing one smi encoding cannot hold the start/length information two smis are used the first having the negative length and the second having the start.

This is in preparation for removing string slices.
Review URL: http://codereview.chromium.org/342015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3153 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/runtime.cc | 51 +++++++++++++++++++++++++++++++++++++++++---------
 src/string.js  |  9 ++++++---
 2 files changed, 48 insertions(+), 12 deletions(-)

diff --git a/src/runtime.cc b/src/runtime.cc
index 8ed13f2398..76520e3aad 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1357,8 +1357,9 @@ class ReplacementStringBuilder {
           StringBuilderSubstringPosition::encode(from);
       AddElement(Smi::FromInt(encoded_slice));
     } else {
-      Handle<String> slice = Factory::NewStringSlice(subject_, from, to);
-      AddElement(*slice);
+      // Otherwise encode as two smis.
+      AddElement(Smi::FromInt(-length));
+      AddElement(Smi::FromInt(from));
     }
     IncrementCharacterCount(length);
   }
@@ -3766,9 +3767,21 @@ static inline void StringBuilderConcatHelper(String* special,
   for (int i = 0; i < array_length; i++) {
     Object* element = fixed_array->get(i);
     if (element->IsSmi()) {
+      // Smi encoding of position and length.
       int encoded_slice = Smi::cast(element)->value();
-      int pos = StringBuilderSubstringPosition::decode(encoded_slice);
-      int len = StringBuilderSubstringLength::decode(encoded_slice);
+      int pos;
+      int len;
+      if (encoded_slice > 0) {
+        // Position and length encoded in one smi.
+        pos = StringBuilderSubstringPosition::decode(encoded_slice);
+        len = StringBuilderSubstringLength::decode(encoded_slice);
+      } else {
+        // Position and length encoded in two smis.
+        Object* obj = fixed_array->get(++i);
+        ASSERT(obj->IsSmi());
+        pos = Smi::cast(obj)->value();
+        len = -encoded_slice;
+      }
       String::WriteToFlat(special,
                           sink + position,
                           pos,
@@ -3789,6 +3802,10 @@ static Object* Runtime_StringBuilderConcat(Arguments args) {
   ASSERT(args.length() == 2);
   CONVERT_CHECKED(JSArray, array, args[0]);
   CONVERT_CHECKED(String, special, args[1]);
+
+  // This assumption is used by the slice encoding in one or two smis.
+  ASSERT(Smi::kMaxValue >= String::kMaxLength);
+
   int special_length = special->length();
   Object* smi_array_length = array->length();
   if (!smi_array_length->IsSmi()) {
@@ -3816,13 +3833,29 @@ static Object* Runtime_StringBuilderConcat(Arguments args) {
   for (int i = 0; i < array_length; i++) {
     Object* elt = fixed_array->get(i);
     if (elt->IsSmi()) {
+      // Smi encoding of position and length.
       int len = Smi::cast(elt)->value();
-      int pos = len >> 11;
-      len &= 0x7ff;
-      if (pos + len > special_length) {
-        return Top::Throw(Heap::illegal_argument_symbol());
+      if (len > 0) {
+        // Position and length encoded in one smi.
+        int pos = len >> 11;
+        len &= 0x7ff;
+        if (pos + len > special_length) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
+        position += len;
+      } else {
+        // Position and length encoded in two smis.
+        position += (-len);
+        // Get the position and check that it is also a smi.
+        i++;
+        if (i >= array_length) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
+        Object* pos = fixed_array->get(i);
+        if (!pos->IsSmi()) {
+          return Top::Throw(Heap::illegal_argument_symbol());
+        }
       }
-      position += len;
     } else if (elt->IsString()) {
       String* element = String::cast(elt);
       int element_length = element->length();
diff --git a/src/string.js b/src/string.js
index d2d6e969df..bb2ad4f2a0 100644
--- a/src/string.js
+++ b/src/string.js
@@ -1,4 +1,4 @@
-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Copyright 2006-2009 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:
@@ -810,10 +810,13 @@ ReplaceResultBuilder.prototype.addSpecialSlice = function(start, end) {
   var len = end - start;
   if (len == 0) return;
   var elements = this.elements;
-  if (start >= 0 && len >= 0 && start < 0x80000 && len < 0x800) {
+  if (start < 0x80000 && len < 0x800) {
     elements[elements.length] = (start << 11) + len;
   } else {
-    elements[elements.length] = SubString(this.special_string, start, end);
+    // 0 < len <= String::kMaxLength and Smi::kMaxValue >= String::kMaxLength,
+    // so -len is a smi.
+    elements[elements.length] = -len;
+    elements[elements.length] = start;
   }
 }