[Webkit-unassigned] [Bug 235581] Add support for WASM branch hinting proposal

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Tue Jan 25 09:48:49 PST 2022


Yusuke Suzuki <ysuzuki at apple.com> changed:

           What    |Removed                     |Added
                 CC|                            |ysuzuki at apple.com

--- Comment #3 from Yusuke Suzuki <ysuzuki at apple.com> ---
Comment on attachment 449921
  --> https://bugs.webkit.org/attachment.cgi?id=449921

View in context: https://bugs.webkit.org/attachment.cgi?id=449921&action=review


> Source/JavaScriptCore/b3/B3EstimateStaticExecutionCounts.cpp:45
>          constexpr double base = 10.0;
> +        if (block->isHinted())
> +            continue;
>          block->setFrequency(pow(base, naturalLoops.loopDepth(block)));

Should we treat the hint as a coefficient to this calculated count?
Let's consider that here is a block in the deep loop (4-depth). Then, the frequency becomes 10e4.
It is much higher than the hint's value (0 or 1.0). So, currently, if we use hint, it lowers the value compared to the value offered by static-execution-counts.

Background: In Wasm B3 IR generator, except for FrequencyClass::Rare, we are not attaching frequency and calculating it in this pass.
In JS, we are using execution counter to profile block's frequency and reflect it at runtime.

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