592631 - JM: fast path for x | 0

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch v1

Consider this micro-benchmark:
-----
function g(a) {
    var res;
    var t0 = new Date;
    
    for(var i=0; i<10000000; i++) {
        var x = i + 0.2;
        res = x | 0;
    }
    print(new Date - t0);
    print(res);
    return res;
}
-----
Performance drops from 785 ms. to 195 ms., about as fast as V8. Which means it's actually faster, because V8 has less loop overhead.

It's quite some code though.. Is there a more efficient way to do this?

Comment 1

[Jan de Mooij [:jandem]]

Btw, this patch also optimizes x << 0.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Patch v2

Woops, use copyDataIntoReg instead of ownRegForData.

Comment 3

[David Anderson [:dvander] - inactive, e-mail if emergency]

Comment on attachment 471086 [details] [diff] [review]
Patch v2


>+    bool lhsIntOrDouble = !(lhs->isNotType(JSVAL_TYPE_DOUBLE) && 
>+        lhs->isNotType(JSVAL_TYPE_INT32));

Nit: second line should indent to the !

>+        rhs->isType(JSVAL_TYPE_INT32) && rhs->getValue().toInt32() == 0 &&
>+        (op == JSOP_BITOR || op == JSOP_LSH)) {
>+        

Nit: No newline here, if it looks too crowded you can put the { on the next line.

Nice work, r=me

Comment 4

[David Mandelin [:dmandelin]]

http://hg.mozilla.org/tracemonkey/rev/ae6ca63c34c3