Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4424,6 +4424,7 @@
 void ScalarEvolution::forgetSymbolicName(Instruction *PN, const SCEV *SymName) {
   SmallVector<Instruction *, 16> Worklist;
   SmallPtrSet<Instruction *, 8> Visited;
+  SmallVector<const SCEV *, 8> ToForget;
   Visited.insert(PN);
   Worklist.push_back(PN);
   while (!Worklist.empty()) {
@@ -4449,12 +4450,13 @@
           !isa<SCEVUnknown>(Old) ||
           (I != PN && Old == SymName)) {
         eraseValueFromMap(It->first);
-        forgetMemoizedResults(Old);
+        ToForget.push_back(Old);
       }
     }
 
     PushDefUseChildren(I, Worklist, Visited);
   }
+  forgetMemoizedResults(ToForget);
 }
 
 namespace {
@@ -7440,6 +7442,7 @@
   if (Result.hasAnyInfo()) {
     SmallVector<Instruction *, 16> Worklist;
     SmallPtrSet<Instruction *, 8> Discovered;
+    SmallVector<const SCEV *, 8> ToForget;
     PushLoopPHIs(L, Worklist, Discovered);
     while (!Worklist.empty()) {
       Instruction *I = Worklist.pop_back_val();
@@ -7457,7 +7460,7 @@
         // own when it gets to that point.
         if (!isa<PHINode>(I) || !isa<SCEVUnknown>(Old)) {
           eraseValueFromMap(It->first);
-          forgetMemoizedResults(Old);
+          ToForget.push_back(Old);
         }
         if (PHINode *PN = dyn_cast<PHINode>(I))
           ConstantEvolutionLoopExitValue.erase(PN);
@@ -7489,6 +7492,7 @@
             Worklist.push_back(I);
         }
     }
+    forgetMemoizedResults(ToForget);
   }
 
   // Re-lookup the insert position, since the call to
@@ -7525,6 +7529,7 @@
   SmallVector<const Loop *, 16> LoopWorklist(1, L);
   SmallVector<Instruction *, 32> Worklist;
   SmallPtrSet<Instruction *, 16> Visited;
+  SmallVector<const SCEV *, 16> ToForget;
 
   // Iterate over all the loops and sub-loops to drop SCEV information.
   while (!LoopWorklist.empty()) {
@@ -7546,8 +7551,8 @@
 
     auto LoopUsersItr = LoopUsers.find(CurrL);
     if (LoopUsersItr != LoopUsers.end()) {
-      for (auto *S : LoopUsersItr->second)
-        forgetMemoizedResults(S);
+      ToForget.insert(ToForget.end(), LoopUsersItr->second.begin(),
+                LoopUsersItr->second.end());
       LoopUsers.erase(LoopUsersItr);
     }
 
@@ -7561,7 +7566,7 @@
           ValueExprMap.find_as(static_cast<Value *>(I));
       if (It != ValueExprMap.end()) {
         eraseValueFromMap(It->first);
-        forgetMemoizedResults(It->second);
+        ToForget.push_back(It->second);
         if (PHINode *PN = dyn_cast<PHINode>(I))
           ConstantEvolutionLoopExitValue.erase(PN);
       }
@@ -7574,6 +7579,7 @@
     // ValuesAtScopes map.
     LoopWorklist.append(CurrL->begin(), CurrL->end());
   }
+  forgetMemoizedResults(ToForget);
 }
 
 void ScalarEvolution::forgetTopmostLoop(const Loop *L) {
@@ -7589,6 +7595,7 @@
   // Drop information about expressions based on loop-header PHIs.
   SmallVector<Instruction *, 16> Worklist;
   SmallPtrSet<Instruction *, 8> Visited;
+  SmallVector<const SCEV *, 8> ToForget;
   Worklist.push_back(I);
   Visited.insert(I);
 
@@ -7598,13 +7605,14 @@
       ValueExprMap.find_as(static_cast<Value *>(I));
     if (It != ValueExprMap.end()) {
       eraseValueFromMap(It->first);
-      forgetMemoizedResults(It->second);
+      ToForget.push_back(It->second);
       if (PHINode *PN = dyn_cast<PHINode>(I))
         ConstantEvolutionLoopExitValue.erase(PN);
     }
 
     PushDefUseChildren(I, Worklist, Visited);
   }
+  forgetMemoizedResults(ToForget);
 }
 
 void ScalarEvolution::forgetLoopDispositions(const Loop *L) {