Bug 22303 – Optimize /^x/ regexps to fail fast

• Component: JavaScriptCore
• Status: RESOLVED WORKSFORME

[Geoffrey Garen]

See bug 18086 -- let's do that optimization in WREC.

Here's what I think can be a layout test:

// Check that an initial ^ will result in a faster match fail.
var s = "a";
var i;

for (i = 0; i < 20; i++)
  s = s + s;

function test(string, regexp)
{
    var start = new Date;
    for (i = 0; i < 100; i++)
        regexp.test(s);
    return new Date - start;
}

var result1 = test(s, /b/);
var result2 = test(s, /^b/);

alert(result1);
alert(result2);

if ((result1 - result2) / result1 > .75)
    testPassed("Congrats, your browser didn't hang!");

testFailed("/^b/ did not discover a match failure faster than /b/");

var successfullyParsed = true;

[Gavin Barraclough]

This optimization now exists in YARR.