[PATCH] D90456: [IndVars] Use more precise context when eliminating narrowing

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyIndVar.cpp:1564
+       Context = User;
+     else if (DT->dominates(User, Context))
+       Context = User;
----------------
anna wrote:
> skatkov wrote:
> > anna wrote:
> > > dominates is a more expensive check than `comesBefore`. We can special case for uses in the same basic block, i.e. :
> > > ```
> > > if (User->getParent() == Context->getParent() && User->comesBefore(Context))
> > >     Context = User
> > > ```
> > comesBefore is used in DT->dominates...
> yes I know :), but there are a bunch of other checks in DT-dominates() which are first checked that are not needed for the same basic block case. Maybe it doesn't make a difference...
But why do you think that the users will be in the same block? In either case, DT checks cost is nothing compared to SCEV creation cost.


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