730786 - IonMonkey: specialize more phis

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

In some cases, type analysis was unable to specialize phis so we could end up with some unnecessary LValueToInt32 instructions. This patch is a small win on some benchmarks like gaussian-blur and access-nsieve.

Comment 1

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

Comment on attachment 600869 [details] [diff] [review]
Patch

Review of attachment 600869 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/ion/IonAnalysis.cpp
@@ +249,5 @@
>              continue;
>          MPhi *use = iter.def()->toPhi();
>          if (!use->triedToSpecialize())
>              continue;
> +        if (use->type() == MIRType_None) {

When do MPhis have MIRType_None?

Comment 2

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

Out of curiosity, is the problem that a phi has an int32 on one edge and a double on another?

Comment 3

[Jan de Mooij [:jandem]]

(In reply to David Anderson [:dvander] from comment #1)
> 
> When do MPhis have MIRType_None?

The algorithm in specializePhis starts like this:

for phi in phis:
   phi.specialize(GuessPhiType(phi))
   ...

GuessPhiType returns MIRType_None if all operands are phis for which triedToSpecialize() returns false. So if the loop visits a phi before visiting its operands (other phis), the phi will have MIRType_None. The patch propagates the operand type when we visit one of the operands (instead of comparing it with MIRType_None and always forcing a Value).

(In reply to David Anderson [:dvander] from comment #2)
> Out of curiosity, is the problem that a phi has an int32 on one edge and a
> double on another?

No but I think that's also worth investigating. I'm pretty sure we will box the value atm but we should be able to specialize such phis as MIRType_Double.

Comment 4

[Jan de Mooij [:jandem]]

https://hg.mozilla.org/projects/ionmonkey/rev/8746ee55dcf9