[PATCH] D155940: [SimplifyCFG] Transform for redirecting phis between unmergeable BB and SuccBB

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Transforms/Utils/Local.cpp:1179
     // To avoid processing the same predecessor more than once.
-    SmallPtrSet<BasicBlock *, 8> SeenPreds;
-    // All predecessors of BB will be moved to Succ.
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XChy wrote:
> nikic wrote:
> > Why is this set no longer needed? Can no predecessors appear multiple times in this code?
> BBPreds is a SmallPtrSet, on which we would not iterate the same predecessor multiple times.
Oh, I missed that this does the updates based on SmallPtrSet now. This is not allowed, because it makes the updates non-deterministic (order matters here). You should replace SmallPtrSet with SmallSetVector to keep order deterministic.


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  https://reviews.llvm.org/D155940/new/

https://reviews.llvm.org/D155940