Restructure RegExp exec cache code.

src/regexp.js

Index: src/regexp.js
diff --git a/src/regexp.js b/src/regexp.js
index 59c40407fbc20ddc4406d0ef2661d7d9bcf39099..f87a5ee18ff8c9000dc4bed15e6d1db4bded574a 100644
--- a/src/regexp.js
+++ b/src/regexp.js
@@ -126,11 +126,11 @@ function RegExpCache() {
   this.regExp = 0;
   this.subject = 0;
   this.replaceString = 0;
-  this.lastIndex = 0;  // Also used for splitLimit when type is "split"
   this.answer = 0;
   // answerSaved marks whether the contents of answer is valid for a cache
   // hit in RegExpExec, StringMatch and StringSplit.
   this.answerSaved = false;
+  this.splitLimit = 0;  // Used only when type is "split".
 }
 
 
@@ -181,22 +181,30 @@ function RegExpExec(string) {
   var cache = regExpCache;
   var saveAnswer = false;
 
+  var lastIndex = this.lastIndex;
+
+  // Since cache.subject is always a string, a matching input can not
+  // cause visible side-effects when converted to a string, so we can omit
+  // the conversion required by the specification.
+  // Likewise, the regexp.lastIndex and regexp.global properties are value
+  // properties that are not configurable, so reading them can also not cause
+  // any side effects (converting lastIndex to a number can, though).
   if (%_ObjectEquals(cache.type, 'exec') &&
-      %_ObjectEquals(cache.lastIndex, this.lastIndex) &&
+      %_ObjectEquals(0, lastIndex) &&
       %_IsRegExpEquivalent(cache.regExp, this) &&
       %_ObjectEquals(cache.subject, string)) {
     if (cache.answerSaved) {
-      // If this regexp is global, cache.lastIndex is zero, so we only get
-      // here if this.lastIndex is zero, and resulting this.lastIndex
-      // must be zero too, so no change is necessary.
-      if (!this.global) this.lastIndex = lastMatchInfo[CAPTURE1];
+      // The regexp.lastIndex value must be 0 for non-global RegExps, and for
+      // global RegExps we only cache negative results, which gives a lastIndex
+      // of zero as well.
+      this.lastIndex = 0;
       return %_RegExpCloneResult(cache.answer);
     } else {
       saveAnswer = true;
     }
   }
 
-  if (%_ArgumentsLength() == 0) {
+  if (%_ArgumentsLength() === 0) {
     var regExpInput = LAST_INPUT(lastMatchInfo);
     if (IS_UNDEFINED(regExpInput)) {
       throw MakeError('no_input_to_regexp', [this]);
@@ -209,41 +217,48 @@ function RegExpExec(string) {
   } else {
     s = ToString(string);
   }
-  var lastIndex = this.lastIndex;
-
-  var i = this.global ? TO_INTEGER(lastIndex) : 0;
+  var global = this.global;
 
-  if (i < 0 || i > s.length) {
-    this.lastIndex = 0;
-    return null;
+  // Conversion is required by the ES5 specification (RegExp.prototype.exec
+  // algorithm, step 5) even if the value is discarded for non-global RegExps.
+  var i = TO_INTEGER(lastIndex);
+  if (global) {
+    if (i < 0 || i > s.length) {
+      this.lastIndex = 0;
+      return null;
+    }
+  } else {
+    i = 0;
   }
 
   %_Log('regexp', 'regexp-exec,%0r,%1S,%2i', [this, s, lastIndex]);
   // matchIndices is either null or the lastMatchInfo array.
   var matchIndices = %_RegExpExec(this, s, i, lastMatchInfo);
 
-  if (matchIndices == null) {
-    if (this.global) {
+  if (matchIndices === null) {
+    if (global) {
+      // Cache negative result only if initial lastIndex was zero.
       this.lastIndex = 0;
-      if (lastIndex != 0) return matchIndices;
+      if (lastIndex !== 0) return matchIndices;
     }
-    cache.lastIndex = lastIndex;
     cache.regExp = this;
-    cache.subject = s;
-    cache.answer = matchIndices;  // Null.
+    cache.subject = s;            // Always a string.
+    cache.answer = null;
     cache.answerSaved = true;     // Safe since no cloning is needed.
     cache.type = 'exec';
     return matchIndices;        // No match.
   }
+
+  // Successful match.
   lastMatchInfoOverride = null;
   var result = BuildResultFromMatchInfo(matchIndices, s);
 
-  if (this.global) {
+  if (global) {
+    // Don't cache positive results for global regexps.
     this.lastIndex = lastMatchInfo[CAPTURE1];
   } else {
     cache.regExp = this;
     cache.subject = s;
-    cache.lastIndex = lastIndex;
     if (saveAnswer) cache.answer = %_RegExpCloneResult(result);
     cache.answerSaved = saveAnswer;
     cache.type = 'exec';
@@ -273,32 +288,49 @@ function RegExpTest(string) {
     }
     string = regExpInput;
   }
-  var s;
-  if (IS_STRING(string)) {
-    s = string;
-  } else {
-    s = ToString(string);
-  }
 
   var lastIndex = this.lastIndex;
+
   var cache = regExpCache;
   if (%_ObjectEquals(cache.type, 'test') &&
       %_IsRegExpEquivalent(cache.regExp, this) &&
       %_ObjectEquals(cache.subject, string) &&
-      %_ObjectEquals(cache.lastIndex, lastIndex)) {
-    // If this regexp is not global, cache.lastIndex is zero, so we only get 
-    // here if this.lastIndex is zero, and resulting this.lastIndex
-    // must be zero too, so no change is necessary.
-    if (this.global) this.lastIndex = lastMatchInfo[CAPTURE1];
+      %_ObjectEquals(0, lastIndex)) {
+    // The regexp.lastIndex value must be 0 for non-global RegExps, and for
+    // global RegExps we only cache negative results, which gives a resulting 
+    // lastIndex of zero as well.
+    if (global) this.lastIndex = 0;
     return cache.answer;
   }
 
+  var s;
+  if (IS_STRING(string)) {
+    s = string;
+  } else {
+    s = ToString(string);
+  }
+  var length = s.length;
+
+  // Conversion is required by the ES5 specification (RegExp.prototype.exec
+  // algorithm, step 5) even if the value is discarded for non-global RegExps.
+  var i = TO_INTEGER(lastIndex);
+  if (global) {
+    if (i < 0 || i > length) {
+      this.lastIndex = 0;
+      return false;
+    }
+  } else {
+    i = 0;
+  }
+
+  var global = this.global;
+
   // Remove irrelevant preceeding '.*' in a test regexp. The expression
   // checks whether this.source starts with '.*' and that the third
   // char is not a '?'
-  if (%_StringCharCodeAt(this.source,0) == 46 && // '.'
-      %_StringCharCodeAt(this.source,1) == 42 && // '*'
-      %_StringCharCodeAt(this.source,2) != 63) { // '?'
+  if (%_StringCharCodeAt(this.source, 0) == 46 &&  // '.'
+      %_StringCharCodeAt(this.source, 1) == 42 &&  // '*'
+      %_StringCharCodeAt(this.source, 2) != 63) {  // '?'
     if (!%_ObjectEquals(regexp_key, this)) {
       regexp_key = this;
       regexp_val = new $RegExp(this.source.substring(2, this.source.length),
@@ -309,33 +341,28 @@ function RegExpTest(string) {
     if (!regexp_val.test(s)) return false;
   }
 
-  var length = s.length;
-  var i = this.global ? TO_INTEGER(lastIndex) : 0;
-
-  cache.type = 'test';
-  cache.regExp = this;
-  cache.subject = s;
-  cache.lastIndex = i;
-
-  if (i < 0 || i > length) {
-    this.lastIndex = 0;
-    cache.answer = false;
-    return false;
-  }
-
   %_Log('regexp', 'regexp-exec,%0r,%1S,%2i', [this, s, lastIndex]);
   // matchIndices is either null or the lastMatchInfo array.
   var matchIndices = %_RegExpExec(this, s, i, lastMatchInfo);
 
-  if (matchIndices == null) {
-    if (this.global) this.lastIndex = 0;
-    cache.answer = false;
-    return false;
+  var result = (matchIndices !== null);
+  if (result) {
+    lastMatchInfoOverride = null;
   }
-  lastMatchInfoOverride = null;
-  if (this.global) this.lastIndex = lastMatchInfo[CAPTURE1];
-  cache.answer = true;
-  return true;
+  if (global) {
+    if (result) {
+      this.lastIndex = lastMatchInfo[CAPTURE1];
+      return true;
+    } else {
+      this.lastIndex = 0;
+      if (lastIndex !== 0) return false;
+    }
+  }
+  cache.type = 'test';
+  cache.regExp = this;
+  cache.subject = s;
+  cache.answer = result;
+  return result;
 }
 
 
@@ -345,12 +372,9 @@ function RegExpToString() {
   // ecma_2/RegExp/properties-001.js.
   var src = this.source ? this.source : '(?:)';
   var result = '/' + src + '/';
-  if (this.global)
-    result += 'g';
-  if (this.ignoreCase)
-    result += 'i';
-  if (this.multiline)
-    result += 'm';
+  if (this.global) result += 'g';
+  if (this.ignoreCase) result += 'i';
+  if (this.multiline) result += 'm';
   return result;
 }