1073587 - Eliminate redundant MaybeCopyElementsForWrite instructions

Status: RESOLVED INVALID

(Core :: JavaScript Engine: JIT, defect, P5)

Description

[Jan de Mooij [:jandem]]

See the script below. For each of the 3 SETELEM's we add MMaybeCopyElementsForWrite, MElements, MInitializedLength, MBoundsCheck.

function f() {
    var x = [1, 2, 3];
    var t = new Date;
    for (var i=0; i<10000000; i++) {
	x[0] = i;
	x[1] = i;
	x[2] = i;
    }
    print(new Date - t);
}
f();

I noticed this on the "Test 0" test in bug 679710 where this is measurably slowing us down.

Comment 1

[Guilherme Lima]

I get 40 for Nightly and 60 for Chrome 43. Is this still a problem?

Comment 2

[Jan de Mooij [:jandem]]

Yeah we still have multiple MaybeCopyElementsForWrite instructions.

Comment 3

[André Bargull [:anba]]

No longer valid, MaybeCopyElementsForWrite was removed in Warp.