[LLVMdev] r156323 - Reassociate FP operands.

[Chad Rosier]

Thanks, Owen.  I'll make sure the canonicalization persists after my change.

-----Original Message-----
From: Owen Anderson [mailto:resistor at mac.com] 
Sent: Monday, June 30, 2014 4:20 PM
To: mcrosier at codeaurora.org
Cc: grosbach at apple.com; llvmdev at cs.uiuc.edu
Subject: Re: r156323 - Reassociate FP operands.

Hi Chad,

As far as I'm aware, CSE is still sensitive to operand sorting to operate
effectively.  If you have a replacement for this functionality, we could
probably remove it, but I don't think we can simply live without it.

-Owen

On Jun 30, 2014, at 12:25 PM, Chad Rosier <mcrosier at codeaurora.org> wrote:

> Owen/All,
> I've been working on adding support for reassociation with unsafe math
> (see: http://reviews.llvm.org/D4129).
> 
> Do you know if this change, r156323, is still necessary?  
> Specifically, do we need the reassociation pass to canonicalize FP 
> operands for CSE to work effectively?  This kinda scares me if it 
> does! :(
> 
> Side note:
> Without this canonicalization, I did see a 3% regression in Mesa 
> because the slp-vectorizer's cost model is sensitive to the ordering of
operands.
> I'm working on reducing a test case now.
> 
> Chad
> 
>