[PATCH PR78114]Refine gfortran.dg/vect/fast-math-mgrid-resid.f
Michael Matz
matz@suse.de
Fri Nov 18 16:52:00 GMT 2016
Hi,
On Thu, 17 Nov 2016, Bin.Cheng wrote:
> B) Depending on ilp, I think below test strings fail for long time with haswell:
> ! { dg-final { scan-tree-dump-times "Executing predictive commoning
> without unrolling" 1 "pcom" { target lp64 } } }
> ! { dg-final { scan-tree-dump-times "Executing predictive commoning
> without unrolling" 2 "pcom" { target ia32 } } }
> Because vectorizer choose vf==4 in this case, and there is no
> predictive commoning opportunities at all.
> Also the newly added test string fails in this case too because the
> prolog peeled iterates more than 1 times.
Btw, this probably means that on haswell (or other archs with vf==4) mgrid
is slower than necessary. On mgrid you really really want predictive
commoning to happen. Vectorization isn't that interesting there.
Ciao,
Michael.
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