[LLVMdev] [X86] DAG Combine - VSELECT

[Eli Friedman]

On Mon, Aug 19, 2013 at 3:34 PM, Juergen Ributzka <juergen at apple.com> wrote:

> Hi @ll,
>
> I am wondering about the use of !isBeforeLegalize in PerformSELECTCombine
> in the X86 backend. This defers all VSELECT related DAG combines until
> after the Legalizer has run. If the IR has already only legal types the
> second round of DAG combines is skipped and no VSELECT specified
> optimizations are performed at all.
>
> Is there a reason we don’t run the X86 DAG combiner before Type
> Legalization?


 I think the code in question is using isBeforeLegalize as a shortcut for
"are all the operand and result types legal".

-Eli
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