diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -661,15 +661,12 @@
 
 // Check V's users to see if it is involved in a reduction in L.
 static PHINode *findInnerReductionPhi(Loop *L, Value *V) {
-  for (Value *User : V->users()) {
-    if (PHINode *PHI = dyn_cast<PHINode>(User)) {
-      if (PHI->getNumIncomingValues() == 1)
-        continue;
-      RecurrenceDescriptor RD;
-      if (RecurrenceDescriptor::isReductionPHI(PHI, L, RD))
-        return PHI;
-      return nullptr;
-    }
+  for (PHINode &PHI : L->getHeader()->phis()) {
+    if (PHI.getNumIncomingValues() == 1 ||
+        !llvm::is_contained(PHI.incoming_values(), V))
+      continue;
+    RecurrenceDescriptor RD;
+    return RecurrenceDescriptor::isReductionPHI(&PHI, L, RD) ? &PHI : nullptr;
   }
 
   return nullptr;