Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5359,6 +5359,13 @@
 }
 
 const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
+  // If the PHI is in the midst of being constructed, it does not make sense to
+  // compute a SCEV for it. Here we assume that for every predecessor block
+  // there is a corresponding incoming value in the PHI.
+  unsigned NumIncoming = PN->getNumIncomingValues();
+  if (!PN->getParent()->hasNPredecessors(NumIncoming))
+    return getUnknown(PN);
+
   if (const SCEV *S = createAddRecFromPHI(PN))
     return S;