Fwd: [PATCH] Select elimination pass

Gerolf Hoflehner ghoflehner at apple.com
Thu Sep 4 11:20:01 PDT 2014

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Begin forwarded message:

> From: Gerolf Hoflehner <ghoflehner at apple.com>
> Subject: Re: [PATCH] Select elimination pass
> Date: September 2, 2014 at 1:43:14 PM PDT
> To: reviews+D5156+public+93dd31b537f620bf at reviews.llvm.org
> This is a good question. InstCombine is a local pattern matcher at the instruction level. I did not want adding a global flavor by introducing the dominator tree in that pass. Also I would have to mess around with the combiner logic when inserting an instruction like an “or” which is not the immediate replacement instruction of the select. I also looked at the SimplifyCFG and if-conversion code, but none seem a natural fit for this optimization. I’m not super happy about a new pass but it looked like the kleinstes Uebel among the choices.
> Cheers
> Gerolf
> On Sep 2, 2014, at 12:59 PM, Chandler Carruth <chandlerc at gmail.com> wrote:
>> Why isn't this an instcombine on select instructions?
>> http://reviews.llvm.org/D5156

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