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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Unite op_get_by_id_with_this with op_get_by_id"
href="https://bugs.webkit.org/show_bug.cgi?id=162124#c28">Comment # 28</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Unite op_get_by_id_with_this with op_get_by_id"
href="https://bugs.webkit.org/show_bug.cgi?id=162124">bug 162124</a>
from <span class="vcard"><a class="email" href="mailto:fpizlo@apple.com" title="Filip Pizlo <fpizlo@apple.com>"> <span class="fn">Filip Pizlo</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=162124#c20">comment #20</a>)
<span class="quote">> (In reply to <a href="show_bug.cgi?id=162124#c19">comment #19</a>)
> > Why would we do this?
>
> If I didn't miss any context *_with_this were created to solve the bug on
> (<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Getter and setter on super are called with wrong "this" object"
href="show_bug.cgi?id=147064">https://bugs.webkit.org/show_bug.cgi?id=147064</a>). The current
> implementationis just a call to slow paths "operation*WithThis", meaning
> that we don't use IC or PIC on "super.foo" for example.
> Merging get_by_id_with_this with op_get_by_id we enable its optimization
> including IC and PIC. In terms of performance, now it means 20% faster over
> op_get_by_id_with_this version.</span >
Then you should make get_by_id_with_this use inline caches.
You shouldn't change get_by_id.
<span class="quote">>
> > It's definitely good for lower tiers that get_by_id does not take an extra
> > this operand. It's also easier to parse. I don't understand why we would
> > remove this optimization.
>
> I didn't understand why it is easier to parse.
> Also, About good parts of get_by_id does not take an extra this operand, do
> you mind explain me why? I can think that we use extra memory to store the
> this operand, which has a big impact because get_by_id is one of the most
> used op_codes.</span >
Compiler analyses always have an O(E) component, where E is the number of data flow edges. One such analysis is the OSR likeness analysis in the DFG and FTL. It's a very expensive analysis and we don't want to make it worse. You're adding a useless "this" data flow edge to every property access. I don't think we want that.
I just want to be very clear: I'm strongly against uniting get_by_id with get_by_id_with_this. Please change your approach to making the unification happen at the PolymorphicAxcess/StructureStubInfo level and please keep these opcodes sepaate.</pre>
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