1136799 - SIMD (interpreter): wrong order of operations on ReciprocalSqrt

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[:ProgramFOX]

Currently, RecSqrt uses `1 / sqrt(x)`, but this is different from the polyfill, which uses `sqrt(1 / x)` [0], which makes a difference [1].
 
  [0]: https://github.com/johnmccutchan/ecmascript_simd/blob/master/src/ecmascript_simd.js#L1248-L1249
  [1]: http://logs.glob.uno/?c=mozilla%23jsapi&s=19+Dec+2014&e=19+Dec+2014&h=order+of+operations#c522774

Comment 1

[:ProgramFOX]

Attachment: Fixed order of operations of RecSqrt

Proposed patch.

Comment 2

[Benjamin Bouvier [:bbouvier] (inactive)]

Comment on attachment 8569314 [details] [diff] [review]
Fixed order of operations of RecSqrt

Review of attachment 8569314 [details] [diff] [review]:
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Yep, nice find! Can you include the fullname in the patch changeset, please? (RecSqrt => ReciprocalSqrt)

Comment 3

[:ProgramFOX]

Attachment: Fixed order of operations of ReciprocalSqrt

New patch, with the commit message updated.

Try push:
https://treeherder.mozilla.org/#/jobs?repo=try&revision=d559e365ed99

Comment 4

[:ProgramFOX]

Try push succeeded (the canceled/failed/busted builds succeeded after retriggering), adding checkin-needed.

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/3bb518882815

Comment 6

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/3bb518882815