Index: llvm/include/llvm/Analysis/ScalarEvolution.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolution.h
+++ llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -560,6 +560,9 @@
   /// expression.
   const SCEV *getSCEV(Value *V);
 
+  /// Return an existing SCEV for V if there is one, otherwise return nullptr.
+  const SCEV *getExistingSCEV(Value *V);
+
   const SCEV *getConstant(ConstantInt *V);
   const SCEV *getConstant(const APInt &Val);
   const SCEV *getConstant(Type *Ty, uint64_t V, bool isSigned = false);
@@ -2057,9 +2060,6 @@
                           SmallPtrSetImpl<Instruction *> &Visited,
                           SmallVectorImpl<const SCEV *> &ToForget);
 
-  /// Return an existing SCEV for V if there is one, otherwise return nullptr.
-  const SCEV *getExistingSCEV(Value *V);
-
   /// Erase Value from ValueExprMap and ExprValueMap.
   void eraseValueFromMap(Value *V);
 
Index: llvm/lib/Transforms/Utils/LCSSA.cpp
===================================================================
--- llvm/lib/Transforms/Utils/LCSSA.cpp
+++ llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -148,13 +148,10 @@
     SSAUpdater SSAUpdate(&LocalInsertedPHIs);
     SSAUpdate.Initialize(I->getType(), I->getName());
 
-    // Force re-computation of I, as some users now need to use the new PHI
-    // node.
-    if (SE)
-      SE->forgetValue(I);
-
     // Insert the LCSSA phi's into all of the exit blocks dominated by the
     // value, and add them to the Phi's map.
+    bool HasSCEV = SE && SE->isSCEVable(I->getType()) &&
+                   SE->getExistingSCEV(I) != nullptr;
     for (BasicBlock *ExitBB : ExitBlocks) {
       if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
         continue;
@@ -202,6 +199,13 @@
       if (auto *OtherLoop = LI.getLoopFor(ExitBB))
         if (!L->contains(OtherLoop))
           PostProcessPHIs.push_back(PN);
+
+      // If we have a cached SCEV for the original instruction, make sure the
+      // new LCSSA phi node is also cached. This makes sures that BECounts
+      // based on it will be invalidated when the LCSSA phi node is invalidated,
+      // which some passes rely on.
+      if (HasSCEV)
+        SE->getSCEV(PN);
     }
 
     // Rewrite all uses outside the loop in terms of the new PHIs we just
Index: llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
+++ llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
@@ -102,7 +102,7 @@
 ; CHECK-NEXT:    [[CMP_EXT:%.*]] = zext i1 [[CMP]] to i8
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP_1]], label [[LOOP_2_HEADER_PREHEADER:%.*]]
 ; CHECK:       loop.2.header.preheader:
-; CHECK-NEXT:    [[CMP_LCSSA:%.*]] = phi i1 [ [[CMP]], [[LOOP_1]] ]
+; CHECK-NEXT:    [[CMP_LCSSA2:%.*]] = phi i1 [ [[CMP]], [[LOOP_1]] ]
 ; CHECK-NEXT:    [[CMP_EXT_LCSSA:%.*]] = phi i8 [ [[CMP_EXT]], [[LOOP_1]] ]
 ; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER:%.*]]
 ; CHECK:       loop.2.header.outer:
@@ -114,7 +114,7 @@
 ; CHECK-NEXT:    i8 4, label [[LOOP_2_HEADER]]
 ; CHECK-NEXT:    ]
 ; CHECK:       loop.2.latch:
-; CHECK-NEXT:    [[CMP_TRUNC_LCSSA1:%.*]] = phi i1 [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ], [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ]
+; CHECK-NEXT:    [[CMP_TRUNC_LCSSA1:%.*]] = phi i1 [ [[CMP_LCSSA2]], [[LOOP_2_HEADER]] ], [ [[CMP_LCSSA2]], [[LOOP_2_HEADER]] ]
 ; CHECK-NEXT:    call void @use(i1 [[CMP_TRUNC_LCSSA1]])
 ; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER]]
 ;
@@ -141,4 +141,63 @@
   br label %loop.2.header
 }
 
+define void @D149435(i16 %arg) {
+; CHECK-LABEL: @D149435(
+; CHECK-NEXT:    br label [[LOOP1:%.*]]
+; CHECK:       loop1:
+; CHECK-NEXT:    [[FR:%.*]] = freeze i16 [[ARG:%.*]]
+; CHECK-NEXT:    [[ARRAYIDX_IDX:%.*]] = shl i16 [[FR]], 1
+; CHECK-NEXT:    [[OR:%.*]] = or i16 [[ARRAYIDX_IDX]], 1
+; CHECK-NEXT:    br i1 false, label [[LOOP1]], label [[LOOP2_PREHEADER:%.*]]
+; CHECK:       loop2.preheader:
+; CHECK-NEXT:    [[FR_LCSSA:%.*]] = phi i16 [ [[FR]], [[LOOP1]] ]
+; CHECK-NEXT:    [[OR_LCSSA:%.*]] = phi i16 [ [[OR]], [[LOOP1]] ]
+; CHECK-NEXT:    [[UMAX:%.*]] = call i16 @llvm.umax.i16(i16 [[OR_LCSSA]], i16 2)
+; CHECK-NEXT:    [[TMP1:%.*]] = add i16 [[UMAX]], -1
+; CHECK-NEXT:    [[TMP2:%.*]] = shl i16 [[FR_LCSSA]], 1
+; CHECK-NEXT:    [[TMP3:%.*]] = sub i16 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i16 [[TMP3]], 0
+; CHECK-NEXT:    [[UMAX1:%.*]] = call i16 @llvm.umax.i16(i16 [[ARG]], i16 2)
+; CHECK-NEXT:    [[TMP5:%.*]] = sub i16 [[UMAX1]], [[ARG]]
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i16 [[TMP5]], 0
+; CHECK-NEXT:    br label [[LOOP2:%.*]]
+; CHECK:       loop2:
+; CHECK-NEXT:    br i1 [[TMP4]], label [[TRAP:%.*]], label [[FOR_BODY8:%.*]]
+; CHECK:       for.body8:
+; CHECK-NEXT:    br i1 [[TMP6]], label [[TRAP]], label [[LOOP2_LATCH:%.*]]
+; CHECK:       loop2.latch:
+; CHECK-NEXT:    br i1 false, label [[LOOP2]], label [[TRAP]]
+; CHECK:       trap:
+; CHECK-NEXT:    unreachable
+;
+  br label %loop1
+
+loop1:
+  %fr = freeze i16 %arg
+  %arrayidx.idx = shl i16 %fr, 1
+  %or = or i16 %arrayidx.idx, 1
+  br i1 false, label %loop1, label %loop2.preheader
+
+loop2.preheader:
+  br label %loop2
+
+loop2:
+  %iv = phi i16 [ %iv.next, %loop2.latch ], [ 0, %loop2.preheader ]
+  %add = add i16 %or, %iv
+  %cmp = icmp ugt i16 %add, 1
+  br i1 %cmp, label %trap, label %for.body8
+
+for.body8:
+  %add2 = add i16 %arg, %iv
+  %cmp2 = icmp ugt i16 %add2, 1
+  br i1 %cmp2, label %trap, label %loop2.latch
+
+loop2.latch:
+  %iv.next = add i16 %iv, 1
+  br i1 false, label %loop2, label %trap
+
+trap:
+  unreachable
+}
+
 declare void @use(i1)