Closed Bug 689779 Opened 10 years ago Closed 10 years ago

IonMonkey: Eliminate negative zero checks for a*a

Categories

(Core :: JavaScript Engine, defect)

defect
Not set
normal

Tracking

()

RESOLVED FIXED

People

(Reporter: dvander, Assigned: terrence)

Details

Attachments

(2 files, 2 obsolete files)

Attached file benchmark
In the attached benchmark, we could get a significant speedup from removing the negative zero check on the multiplication. We should be able to do this in MIR by seeing that (a * a) will never be negative.
Attached patch First attempt. (obsolete) — Splinter Review
Speedup is 1.12x, but I need some feedback on the patch's specifics:

1) I think isCongruent is a more specific (and costly) test that we want for this, but I could be quite wrong.

2) Is there a way to implement this check without having to copy the body of MBinaryArithInstruction::foldsTo?

3) Should I add a setter for canBeNegativeZero_?
Assignee: general → tcole
Status: NEW → ASSIGNED
Attachment #563502 - Flags: feedback?(dvander)
Attached patch v2 (obsolete) — Splinter Review
Shorter patch using congruentTo and calling out to super (requires us to re-acquire lhs/rhs).  It seems to be epsilon slower than v1 in the benchmark, but it's well within the error bars.
Attachment #563524 - Flags: feedback?(dvander)
Comment on attachment 563524 [details] [diff] [review]
v2

Nice.
Attachment #563524 - Flags: feedback?(dvander) → review+
Attachment #563502 - Attachment is obsolete: true
Attachment #563502 - Flags: feedback?(dvander)
Attached patch rebasedSplinter Review
I still don't have commit access, but that's no reason to let this bitrot.
Attachment #563524 - Attachment is obsolete: true
Attachment #567918 - Flags: checkin?(dvander)
https://hg.mozilla.org/projects/ionmonkey/rev/80f0dce7aa2e
Status: ASSIGNED → RESOLVED
Closed: 10 years ago
Resolution: --- → FIXED
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