Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1234,6 +1234,7 @@
         WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
         IRBuilder<> Builder(&*WidePhi->getParent()->getFirstInsertionPt());
         Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType());
+        SE->forgetValue(UsePhi);
         UsePhi->replaceAllUsesWith(Trunc);
         DeadInsts.emplace_back(UsePhi);
         LLVM_DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi << " to "
Index: llvm/lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1314,13 +1314,6 @@
       if (!SE->isSCEVable(PN->getType()))
         continue;
 
-      // It's necessary to tell ScalarEvolution about this explicitly so that
-      // it can walk the def-use list and forget all SCEVs, as it may not be
-      // watching the PHI itself. Once the new exit value is in place, there
-      // may not be a def-use connection between the loop and every instruction
-      // which got a SCEVAddRecExpr for that loop.
-      SE->forgetValue(PN);
-
       // Iterate over all of the values in all the PHI nodes.
       for (unsigned i = 0; i != NumPreds; ++i) {
         // If the value being merged in is not integer or is not defined
@@ -1441,6 +1434,13 @@
       continue;
     }
 
+    // It's necessary to tell ScalarEvolution about this explicitly so that
+    // it can walk the def-use list and forget all SCEVs, as it may not be
+    // watching the PHI itself. Once the new exit value is in place, there
+    // may not be a def-use connection between the loop and every instruction
+    // which got a SCEVAddRecExpr for that loop.
+    SE->forgetValue(Phi.PN);
+
     NumReplaced++;
     Instruction *Inst = cast<Instruction>(PN->getIncomingValue(Phi.Ith));
     PN->setIncomingValue(Phi.Ith, ExitVal);