[PATCH] D105921: [SCEV] Handle zero stride correctly in howManyLessThans

[Eli Friedman via Phabricator via llvm-commits]

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

LGTM



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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:11675
+      auto *StartIfZero = getMinusSCEV(IV->getStart(), Stride);
+      return isLoopEntryGuardedByCond(L, Cond, StartIfZero, RHS);
+    };
----------------
reames wrote:
> efriedma wrote:
> > We make exactly the same isLoopEntryGuardedByCond() call later; can we avoid calling it twice?
> I assume you're concerned about compile time?  If so, I'd prefer to land the simple change (this one), and then revisit if needed.  I would not be surprised if the later one changed form anyways.  
As a practical matter, I'm not really concerned about compile-time here, I guess; we should be hitting wouldZeroStrideBeUB() very rarely in real code.  Just feels a little weird.  I'm okay landing this as-is for now, and we can consider refactoring once we're confident we're actually performing all the checks we need.


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https://reviews.llvm.org/D105921