[LLVMdev] RFC: Should we have (something like) -extra-vectorizer-passes in -O2? (original) (raw)

Hal Finkel hfinkel at anl.gov
Tue Oct 14 10:47:55 PDT 2014

----- Original Message -----

From: "Chandler Carruth" <chandlerc at google.com> To: "Hal Finkel" <hfinkel at anl.gov> Cc: "Andrew Trick" <atrick at apple.com>, "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>, "James Molloy" <james at jamesmolloy.co.uk> Sent: Tuesday, October 14, 2014 12:41:38 PM Subject: Re: [LLVMdev] RFC: Should we have (something like) -extra-vectorizer-passes in -O2?

On Tue, Oct 14, 2014 at 10:28 AM, Hal Finkel < hfinkel at anl.gov > wrote: > I think it’s generally useful to have an “extreme” level of > optimization without much regard for compile time, and in that > scenario this pipeline makes sense. But this is hardly something > that should happen at -O2/-Os, unless real data shows otherwise. Doing all this only at >= -O3 does not seem unreasonable to me. FWIW, I think we're being overly conservative if we're relegating these to -O3 when the total cost is 2%. That doesn't seem like the right tradeoff.

While I think it is not unreasonable not to do it, I also think it would be reasonable to do it. Late cleanup is currently a place where we could use some improvement.

I actually agree that the set I proposed is on the aggressive end --

I did say 'all' ;)

that was the point -- but we have more than 2% fluctuations in the optimizers' runtime from month to month. If we want to rip stuff out it should be because of a principled reason that it isn't going to help the code in that phase.

I completely agree.

-Hal

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

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