451788 - TM: Multiplying, dividing, modulo two integers promotes to double

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P5)

Description

[Boris Zbarsky [:bzbarsky]]

The minimal shell testcase in bug 451673 has this line:

  limit = i * 1;

Here 'i' is an integer counter.  As far as I can tell, the tracer treats 'i' as an integer, and of course 1 is an integer, but the product is promoted to double. It might be worth it to bounds-check and not promote if we won't overflow.

Comment 1

[Andreas Gal :gal]

I intentionally didn't demote this since multiplications often overflow (they do in one of the sunspider benchmarks). But yes, we should give this another try.

Comment 2

[Andreas Gal :gal]

Changed title to include division as well (which implies modulo too).

Comment 3

[Andreas Gal :gal]

Modulo by a non-zero constant is easy and helps 3d-raytrace:

http://hg.mozilla.org/tracemonkey/rev/87fe68f51647

Comment 4

[Andreas Gal :gal]

Backed out the previous patch again until its fixed. 

http://hg.mozilla.org/tracemonkey/rev/61b9209c186f

Comment 5

[Andreas Gal :gal]

Attachment: Patch, this time hopefully working.

Comment 6

[Brendan Eich [:brendan]]

Comment on attachment 338850 [details] [diff] [review]
Patch, this time hopefully working.

>+/*
>+ * Note: Caller is responsible for ensuring that b is not 0, or really bad things are going to
>+ *       happen.

This would look nicer if wrapped before column 80 -- most comments do.

>+          case F_dmod: 
>+            JS_ASSERT(s0->isQuad() && args[1]->isQuad());
>+            if (args[1]->isconstq() && args[1]->constvalq() && isPromote(s0)) {
>+                LIns* args2[] = { demote(out, s0), demote(out, args[1]) };
>+                return out->ins1(LIR_i2f, out->insCall(F_imod, args2));

Could you comment with a FIXME: bug NNNNNN where the bug number is the one about adding LIR_imod?

/be

Comment 7

[Andreas Gal :gal]

http://hg.mozilla.org/tracemonkey/rev/b8f1727c3c5b

Comment 8

[Damon Sicore (:damons)]

Not a blocker as it's an enhancement.