[PATCH] D13064: Add CFG Simplification pass after Loop Unswitching.

hfinkel@anl.gov via llvm-commits llvm-commits at lists.llvm.org
Wed Sep 23 19:09:33 PDT 2015

hfinkel accepted this revision.
hfinkel added a comment.
This revision is now accepted and ready to land.

In http://reviews.llvm.org/D13064#252353, @mzolotukhin wrote:

> Hi Hal,
> > What's the overall change to the pass/analysis schedule? I'd tend to think that putting it after InstCombine would be better so it would not need to recompute DT again for InstCombine.
> That shouldn't matter because `InstCombine` preserves DominatorTree - so we'll rebuild it after `SimplifyCFG` only once. If we run `SimplifyCFG` after `InstCombine`, we invoke `Basic Alias Analysis (stateless AA impl)` twice (, but as far as I understand it's almost free.


Okay, thanks. Indeed, in this case, constructing the DT after SimplifyCFG is probably going to be cheaper (or the same cost) as constructing it before hand, so keeping it before InstCombine is probably better. LGTM.


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