Simplify regexp test call when the regexp starts and ends with '.*'.

src/regexp.js

Index: src/regexp.js
===================================================================
--- src/regexp.js	(revision 4793)
+++ src/regexp.js	(working copy)
@@ -257,6 +257,10 @@
 }
 
 
+// One-element cache for the simplified test regexp.
+var regexp_key;
+var regexp_val;

[Lasse Reichstein, 2010/06/04 11:30:33]

How often do you hit this? (And how often will you hit it if you cache negative
results in the global regexp cache)?

[sandholm, 2010/06/04 11:57:23]

Caching negative results in the global regexp cache won't change the hit rate
for this cache as test is often called with a new string.

+
 // Section 15.10.6.3 doesn't actually make sense, but the intention seems to be
 // that test is defined in terms of String.prototype.exec. However, it probably
 // means the original value of String.prototype.exec, which is what everybody
@@ -281,9 +285,7 @@
   }
 
   var lastIndex = this.lastIndex;
-
   var cache = regExpCache;
-
   if (%_ObjectEquals(cache.type, 'test') &&
       %_ObjectEquals(cache.regExp, this) &&
       %_ObjectEquals(cache.subject, string) &&
@@ -291,6 +293,26 @@
     return cache.answer;
   }
 
+  // Remove irrelevant '.*' around a test regexp. The expression  
+  // checks whether this.source starts and ends with '.*' and that the third 
+  // char is not a '?' and that the third to last char is not a '\'. 
+  if (%_StringCharCodeAt(this.source,0) == 46 && // '.'

[Lasse Reichstein, 2010/06/04 11:30:33]

You may want to try moving this.source to a local variable. It is used a lot.
Ditto for this.source.length.

[sandholm, 2010/06/04 11:57:23]

Tried this. Causes regressions on some benchmarks

+      %_StringCharCodeAt(this.source,1) == 42 && // '*' 
+      %_StringCharCodeAt(this.source,2) != 63 && // '?'
+      %_StringCharCodeAt(this.source,this.source.length - 3) != 28 && // '\'
+      %_StringCharCodeAt(this.source,this.source.length - 2) == 46 && // '.'   
+      %_StringCharCodeAt(this.source,this.source.length - 1) == 42) { // '*'
+    if (!%_ObjectEquals(regexp_key, this)) {
+      regexp_key = this; 
+      regexp_val = new $RegExp(this.source.substring(2,
+                                                     this.source.length - 2),
+                               (this.global ? 'g' : '')
+                               + (this.ignoreCase ? 'i' : '')
+                               + (this.multiline ? 'm' : ''));
+    }
+    if (!regexp_val.test(s)) return false;

[Lasse Reichstein, 2010/06/04 11:30:33]

You can cache the negative result in the regexp cache here (using the original
regexp as key). That means that next time you call test, the global regexp cache
will match and you don't even get here.

[sandholm, 2010/06/04 11:57:23]

Often test is called with a new string so that won't really pay off in the end.

+  }
+  
   var length = s.length;
   var i = this.global ? TO_INTEGER(lastIndex) : 0;
 
@@ -299,7 +321,7 @@
   cache.subject = s;
   cache.lastIndex = i;
 
-  if (i < 0 || i > s.length) {
+  if (i < 0 || i > length) {
     this.lastIndex = 0;
     cache.answer = false;
     return false;