[llvm] r339722 - NFC: Clarify comment in loop vectorization legality

[Anna Thomas via llvm-commits]

Author: annat
Date: Tue Aug 14 13:25:13 2018
New Revision: 339722

URL: http://llvm.org/viewvc/llvm-project?rev=339722&view=rev
Log:
NFC: Clarify comment in loop vectorization legality

Clarifying the comment about PSCEV and external IV users by referencing
the bug in question.

Modified:
    llvm/trunk/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp?rev=339722&r1=339721&r2=339722&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp Tue Aug 14 13:25:13 2018
@@ -563,7 +563,8 @@ void LoopVectorizationLegality::addInduc
   // back into the PHI node may have external users.
   // We can allow those uses, except if the SCEVs we have for them rely
   // on predicates that only hold within the loop, since allowing the exit
-  // currently means re-using this SCEV outside the loop.
+  // currently means re-using this SCEV outside the loop (see PR33706 for more
+  // details).
   if (PSE.getUnionPredicate().isAlwaysTrue()) {
     AllowedExit.insert(Phi);
     AllowedExit.insert(Phi->getIncomingValueForBlock(TheLoop->getLoopLatch()));