1377489 - Eliminate a useless copy under FunctionToString

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

Noticed this while looking at bug 1377343. Right now we get the function's source code as JSString (including malloc + copying/Latin1-izing chars) then we append this string to a StringBuffer. That's just silly since we can pass a StringBuffer and append directly to that.

The attached patch does this. For the micro-benchmark below I get:

before: 592 ms
after:  435 ms

Still a lot of slowness here but it's a decent win.

function test() {
    var s = "";
    for (var i = 0; i < 1000; i++)
        s += "var x = 10;";
    var f = Function(s);
    var t = new Date;
    for (var i = 0; i < 50000; i++)
        s = f.toString();
    alert(new Date - t);
}

test();

Comment 1

[Luke Wagner [:luke]]

Comment on attachment 8882603 [details] [diff] [review]
Patch

Review of attachment 8882603 [details] [diff] [review]:
-----------------------------------------------------------------

Good observation.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/f48357605b40
Eliminate unnecessary string allocation + copy under FunctionToString. r=luke

Comment 3

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/f48357605b40