Status: New
Owner: ----
New issue 2648 by yukoba: Using i = (i + 1) | 0 on loop variable is slow on
ARM
http://code.google.com/p/v8/issues/detail?id=2648
Following benchmark 1 and benchmark 2 should run by the same speed,
but benchmark 2 is very slow on Chrome 27 on ARM. V8 is 3.17.6.8.
I changed it from "i++" to "i = (i + 1) | 0".
This does not happen on Chrome 27 (x86), Firefox 21 (x86 or ARM) or Safari
(iOS).
Benchmark 1 (Snapdragon S3)
Chrome 27: 1200ms
Firefox 21: 1600ms
Benchmark 2 (Snapdragon S3)
Chrome 27: 9950ms
Firefox 21: 1600ms
I checked this also happens on Tegra 3 and Exynos 4.
function benchmark1() {
var sum = 0;
for (var i = 0; i < 200; i++) {
for (var j = 0; j < 1000000; j++) {
sum = (sum + j) | 0;
}
}
return sum;
}
function benchmark2() {
var sum = 0;
for (var i = 0; i < 200; i = (i + 1) | 0) {
for (var j = 0; j < 1000000; j++) {
sum = (sum + j) | 0;
}
}
return sum;
}
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