[PATCH] D44001: [SCEV] Prove implications for SCEVUnknown Phis

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


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Comment at: llvm/trunk/lib/Analysis/ScalarEvolution.cpp:9604
+    auto *Preheader = RLoop->getLoopPreheader();
+    assert(Preheader && "Loop with AddRec with no preheader?");
+    const SCEV *L1 = getSCEV(LPhi->getIncomingValueForBlock(Preheader));
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mkazantsev wrote:
> efriedma wrote:
> > This assertion is triggering on the polly-AOSP buildbot: http://lab.llvm.org:8011/builders/aosp-O3-polly-before-vectorizer-unprofitable/builds/477 .
> > 
> > I can try to reduce a testcase if you need it, but the assertion is pretty obviously just wrong: in general, SCEV doesn't care care whether a loop has a preheader.
> Thanks Eli, you're right, we don't actually need preheader here. I think this one should fix that: https://reviews.llvm.org/rL329379
Hmm...

That's an improvement, but ScalarEvolution::createAddRecFromPHI is still much more generous than your assertions: it handles loops with multiple predecessors and multiple latches, at least in some cases.


Repository:
  rL LLVM

https://reviews.llvm.org/D44001