[PATCH] Unrolling improvements (target indep. and for x86)

[Hal Finkel]

----- Original Message -----
> From: "Chandler Carruth" <chandlerc at google.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Diego Novillo" <dnovillo at google.com>, "llvm-commits" <llvm-commits at cs.uiuc.edu>, "Nadav Rotem"
> <nrotem at apple.com>
> Sent: Thursday, March 6, 2014 1:42:38 PM
> Subject: Re: [PATCH] Unrolling improvements (target indep. and for x86)
> 
> 
> 
> 
> 
> On Mon, Mar 3, 2014 at 2:54 PM, Hal Finkel < hfinkel at anl.gov > wrote:
> 
> 
> However, Chandler had made a similar change to the loop vectorizer
> (to prefer power-of-2 unrolling factors), because it helps with X86
> addressing modes, and as a result, I wonder whether it is worth
> keeping this part regardless. Chandler?
> To try and answer this specifc question first:
> 
> 
> The power-of-two thing is an interesting and pesky issue. I suspect
> that it matters more for "widening" style unrolls than for this
> version. Consider that in the widening version, we need to have all
> N unroll-step pointers live at the same time (potentially), whereas
> here we can just lea them however we like on each unrolled
> iteration.
> 
> 
> So I wouldn't include it until we have benchmarks showing it matters.
> 
> 
> 
> 
> Regarding the entire patch series, please at least commit everything
> but the gep-cost-metric change at least. I'm more hesitant there and
> would like to stare at the patch a bit.

I committed the optimization pipeline change in r205264. Next I'll commit the change to set the x86 unrolling preferences, but not until later tonight or tomorrow.

 -Hal

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory