[llvm] r222142 - [Reassociate] As the expression tree is rewritten make sure the operands are

[Kevin Qin]

Hi Chad,

We found this commit introduced a correctness problem on AArch64. Coremark
is failed on performance test due to result miscompare, and 403.gcc in
SPEC2006 got problem in run time.

I think it should be easy to reproduce those problems. Please have a look
at this.

Thanks,
Kevin

2014-11-18 19:12 GMT+00:00 Chad Rosier <mcrosier at codeaurora.org>:

> Thanks for the info, Suyong.  I'm pretty sure the change is trivially
> correct.  It's very likely this commit perturbed a lot of IR.  Prior to my
> recent commits the IR that was coming out of the pass was largely
> unordered.
>
>  Chad
>
> > Hi Chad, Timur
> >
> > Just wanted to make a point here.
> >
> > This patch actually eased further transformations like SLP Vectoization.
> >
> > Test case :
> >
> > sum = a[0] + a[1] + a[2] + a[3]
> >
> > Earlier, without this patch, re-associate pass would re-organize this
> > expression into
> >
> > sum = (((a[1] + a[0]) + a[2]) + a[3])
> >
> > which made SLP vectorizer difficult to identify this type of horizontal
> > reduction.
> > With this patch, the expression would remain
> >
> > sum = (((a[0] + a[1]) + a[2]) + a[3])
> >
> > which made SLP vectorizer task simpler.
> >
> > Patch holds good value for further optimization passes,
> > though as Timur reports that its breaking some test cases.
> >
> > --
> > With regards,
> > Suyog Sarda
> >
>
>
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-- 
Best Regards,

Kevin Qin
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