Regexp: Remove nodes from the regexp that cannot match because

test/mjsunit/regexp-capture-3.js

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
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 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 136 matching lines @@
 // failure that came after.
 "bar.foo baz......".replace(/(ba.).*?f/g, function() { return "x";});
 assertEquals("bar", RegExp.$1);
 
 
 var a = "foo bar baz".replace(/^|bar/g, "");
 assertEquals("foo  baz", a);
 
 a = "foo bar baz".replace(/^|bar/g, "*");
 assertEquals("*foo * baz", a);
+
+// A regexp that will backtrack forever.  However it can never match
+// on an ASCII regexp because it has a forced non-ASCII character.
+// Test that we detect regexps that can never match on ASCII strings.
+var re = /(((.*)*)*)å/;
+"This is an ASCII string that could take forever".match(re);

[ulan, 2012/04/25 12:55:28]

Could you please add more tests?
At least one for each of the node types that have FilterAscii.