Fix ScalarEvolutionExpander when creating a PHI in a block with duplicate predecessors

It seems that when I fixed this, almost exactly a year ago, I did not quite do
it correctly. When we have duplicate block predecessors, we can indeed not have
different incoming values for the same block, but we *must* have duplicate
entries. So, instead of skipping the duplicates, we explicitly add the
duplicate incoming values.

Fixes PR20442.

llvm-svn: 214423

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index 8c75b0db70f..968c619a48d 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1443,8 +1443,12 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
     Constant *One = ConstantInt::get(Ty, 1);
     for (pred_iterator HPI = HPB; HPI != HPE; ++HPI) {
       BasicBlock *HP = *HPI;
-      if (!PredSeen.insert(HP))
+      if (!PredSeen.insert(HP)) {
+        // There must be an incoming value for each predecessor, even the
+        // duplicates!
+        CanonicalIV->addIncoming(CanonicalIV->getIncomingValueForBlock(HP), HP);
         continue;
+      }
 
       if (L->contains(HP)) {
         // Insert a unit add instruction right before the terminator