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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [JSC] implement async functions proposal"
href="https://bugs.webkit.org/show_bug.cgi?id=156147#c112">Comment # 112</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [JSC] implement async functions proposal"
href="https://bugs.webkit.org/show_bug.cgi?id=156147">bug 156147</a>
from <span class="vcard"><a class="email" href="mailto:utatane.tea@gmail.com" title="Yusuke Suzuki <utatane.tea@gmail.com>"> <span class="fn">Yusuke Suzuki</span></a>
</span></b>
<pre>Comment on <span class=""><a href="attachment.cgi?id=280020&action=diff" name="attach_280020" title="Patch">attachment 280020</a> <a href="attachment.cgi?id=280020&action=edit" title="Patch">[details]</a></span>
Patch
View in context: <a href="https://bugs.webkit.org/attachment.cgi?id=280020&action=review">https://bugs.webkit.org/attachment.cgi?id=280020&action=review</a>
<span class="quote">>>>>> Source/JavaScriptCore/parser/Parser.cpp:624
>>>>> + if (UNLIKELY(m_runtimeFlags.isAsyncAwaitEnabled() && matchContextualKeyword(m_vm->propertyNames->async))) {
>>>>
>>>> There is a chance that this may be faster if the LHS and RHS were swapped because it might aid the register allocator.
>>>> Same with the similar compare elsewhere.
>>>> Is this what's slowing down the parser?
>>>> Have you tried making ASYNC a key word? That may be faster than checking the IDENT's StringImpl
>>>
>>> When executing `matchContextualKeyword(m_vm->propertyNames->async)`, it becomes `Identifier == Identifier` check and it should be pointer comparison because Identifier is already interned.
>>
>> I was just thinking that we may get almost identical codegen (or we would get slightly worse codegen but the machine's branch/indirect jump prediction would make up for it) for the 'switch' statement if we made ASYNC a keyword, and we wouldn't have this branch at each IDENT. But maybe this would cause slow downs elsewhere. I'm not sure. It's hard to predict without implementing it and measuring perf.
>
> Actually, a good starting point is to see if these branches are actually what the remaining slow down is. Because octane/code-load doesn't use async/await, we can probably get away with removing the branch and seeing if the entire regression goes away. If it doesn't, we know there is slow down elsewhere.</span >
Sounds reasonable.</pre>
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