[llvm] r204699 - SLP vectorizer: Don't hoist vector extracts of phis.

[Tobias Grosser]

On 03/25/2014 03:18 AM, Andrew Trick wrote:
> Author: atrick
> Date: Mon Mar 24 21:18:47 2014
> New Revision: 204699
>
> URL: http://llvm.org/viewvc/llvm-project?rev=204699&view=rev
> Log:
> SLP vectorizer: Don't hoist vector extracts of phis.
>
> Extracts coming from phis were being hoisted, while all others were
> sunk to their uses. This was inconsistent and didn't seem to serve a
> purpose. Changing all extracts to be sunk to uses is a prerequisite
> for adding block frequency to the SLP vectorizer's cost model.
>
> I benchmarked the change in isolation (without block frequency). I
> only saw noise on x86 and some potentially significant improvements on
> ARM. No major regressions is good enough for me.

Hi Andrew,

my performance testers spotted a 37% performance regression for 
fp-convert. In the set of five relevant commits there are only debug 
info changes, lldb changes and your commit:

http://llvm.org/perf/db_default/v4/nts/graph?plot.0=34.161.2&highlight_run=23986

I am not insisting to investigate this, but wanted to give you at least 
this information.

Cheers,
Tobias