[PATCH] D100004: [SCEV] Correct handling of recurrences matched in partially unreachable code (try 2)

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:5675
   auto *L = LI.getLoopFor(P->getParent());
-  assert(L && L->getHeader() == P->getParent());
-  if (!L->contains(BO->getParent()))
+  if (!L || L->getHeader() != P->getParent())
+    // If we have unreachable blocks involved, then dominance collapses and
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reames wrote:
> mkazantsev wrote:
> > Do we have a guarantee of having no loops in unreachable code?
> See LoopInfoBase<>::analyze specififically the line:
> DomTree.isReachableFromEntry(Backedge))
> 
> Note that the verify routine also checks against a newly constructed LI, so any failure to update should be caught in a expensive asserts run.
But expensive verification runs between the passes. It is still possible that some pass makes a loop unreachable in the middle of the transform and does not immediately destroy the loop while continuing to use SCEV.

I am still strongly leaning towards not relying on such things, even if they might be correct. It's far from obvious and far from simple.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D100004/new/

https://reviews.llvm.org/D100004