[PATCH] reenable gep merging in some constrainted cases

[Quentin Colombet]

Hi David,

> On May 19, 2015, at 3:26 PM, Xinliang David Li <xinliangli at gmail.com> wrote:
> 
> I agree. I remembered the plan was to disable the blind GEP merging which have shown big damages to performance, reported independently by different users, and tune the  heuristic to enable beneficial merging selectively. 

My concern is that we will end up tuning a heuristic before having really think about our alternative. Since we are still in the early stage of this, I was wondering if it wouldn’t be best to step back and have a better understanding of our options.

My initial approval for the plan was based on the fact that we did not see any actual regressions, but it seems it was not the case.

Thoughts?

Cheers,
-Quentin

> 
> David
> 
> 
> On Tue, May 19, 2015 at 3:10 PM, Wei Mi <wmi at google.com <mailto:wmi at google.com>> wrote:
> Hi Quentin,
> 
> Yes, it is a tuning of the heuristic from http://reviews.llvm.org/D8911 <http://reviews.llvm.org/D8911>.
> 
> Because the regression I saw here has much smaller negative impact
> compared with the original negative impact of gep merging, is it
> possible that we leave r235455 there while we discuss a better fix?
> Because in this way we can check is there any other analysis affected
> by disabling gep merging.
> 
> Thanks,
> Wei.
> 
> On Tue, May 19, 2015 at 3:00 PM, Quentin Colombet <qcolombet at apple.com <mailto:qcolombet at apple.com>> wrote:
> > Hi Wei,
> >
> > Correct me if I am wrong, but this is a tuning of the heuristic from http://reviews.llvm.org/D8911 <http://reviews.llvm.org/D8911>, right?
> >
> > Given that you actually see a regression now (and the fact that after discussing with Chandler, I am not convinced the initial change makes sense), I would suggest that you revert r235455 and that we start again the discussion on how to properly fix that.
> >
> > Thanks,
> > -Quentin
> >
> >
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> > http://reviews.llvm.org/D9865 <http://reviews.llvm.org/D9865>
> >
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