[Webkit-unassigned] [Bug 159859] DFG CSE should know how to decay a MultiGetByOffset

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=159859

--- Comment #2 from Filip Pizlo <fpizlo at apple.com> ---
(In reply to comment #1)
> Is MultiGetByOffset not dominated by a StructureCheck the way GetByOffset is?

It's not dominated by a CheckStructure.  The MultiGetByOffset does its own structure check.

We want one switch statement that both checks that we have the structure we want and loads the value.  CheckStructure with multiple structures in its set will be a switch and MultiGetByOffset is always a switch (unless we failed to strength-reduce a one-case MultiGetByOffset), so that would be two switches.  That's not cool, because we can't guarantee that B3 will jump-thread or tail-dup two switches in a row.  So, MultiGetByOffset is its own check.

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