[LLVMdev] r156323 - Reassociate FP operands.

[Owen Anderson]

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
> 
>