1077305 - Atomics: Generate better code for accesses to Uint32 arrays

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect, P5)

Description

[Lars T Hansen [:lth]]

This is followup work to bug 979594.

The operations on SharedUint32Array will only be inlined if the predicted result type of the operation is Uint32.  That is too pessimistic, because frequently a SharedUint32Array will only contain values that are in the Int32 range and so the predicted (observed) result type may be Int32.

We probably can't quite use the same technique as for LoadTypedArrayElement, which will predict the type to be Int32 and bail if the prediction fails, since some of the operations in question - compareExchange, add, sub, and, or, xor - are not idempotent.

It's possible that the best solution is to force the return type to Double, in order to get predictable performance and acceptable semantics.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1077305: Return Double for Atomics on Uint32 TypedArrays. r=jandem!

Change Atomics for Uint32 TypedArrays to use Double-typed numbers. That way we
get a stable return type (always Double typed instead of Int32 or Double typed),
which ensures we get a deterministic inlining behaviour in Ion and make it
possible to inline Atomics functions for Uint32 in Warp.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/701d9a09a5bf
Return Double for Atomics on Uint32 TypedArrays. r=jandem

Comment 3

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/701d9a09a5bf