[Webkit-unassigned] [Bug 152162] B3 should have general sinking and this should even work with Check

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Dec 10 18:56:11 PST 2015


https://bugs.webkit.org/show_bug.cgi?id=152162

--- Comment #1 from Filip Pizlo <fpizlo at apple.com> ---
(In reply to comment #0)
> B3 should sink sinkable operations to the lowest dominating point in the
> CFG. In case an operation's output is only used for the stackmap of Check,
> we should turn this:
> 
>     @a = Foo(...)
>     Check(@p, @a)
> 
> into this:
> 
>     Branch(@p, #exit, #continuation)
> 
>   exit:
>     @a = Foo(...)
>     Check(false, @a)
> 
>   contination:
>     ...
> 
> This will help with the useless Shr that we will see on some array bounds
> checks from asm.js code.

It's worth saying that usually, https://bugs.webkit.org/show_bug.cgi?id=152160 will obviate the need for this. But things may leak past that optimization. This optimization is more general, but it has a compile time cost due to the introduction of control flow.

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