578917 - inline js_UnboxDouble

Status: RESOLVED DUPLICATE of bug 580534

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

With fatvals, phi nodes, and uint64-to-double conversion, we can inline js_UnboxDouble on both 32 and 64 bit.

Comment 1

[Luke Wagner [:luke]]

I was investigating fatval slowdowns on individual SS benchmarks math-cordic was one (2ms slowdown).  Shark seems to indicate that this is entirely due to js_UnboxDouble.  This bug should improve things.

Comment 2

[Nicholas Nethercote [inactive]]

Note that accesses to type-specific arrays, ie. arrays-of-doubles (bug 566767) don't have the js_UnboxDouble call.  So this bug and that bug are both eating into the same inefficiency, but not in a complementary way.

Comment 3

[Andreas Gal :gal]

There are two ways to fix this. Not doing d2i would allow us to not emit a call for UnboxDouble (which we currently need to detect it and turn it into UnboxInt32 where needed). Nick owns a bug on that, but it seems hard.

Another approach would be to finish the call inlining patch and inline with that:

https://bugzilla.mozilla.org/show_bug.cgi?id=522593

Comment 4

[Luke Wagner [:luke]]

(In reply to comment #3)
> There are two ways to fix this. Not doing d2i would allow us to not emit a call
> for UnboxDouble (which we currently need to detect it and turn it into
> UnboxInt32 where needed). Nick owns a bug on that, but it seems hard.

I'm not sure which approach you are referring to, but all I want to do is:
1. generate the little diamond graph to unbox the double, using a phi node
2. replace the places where we ask "is it a js_UnboxDouble" with a structural match on the diamond generated in (1)