Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1121,6 +1121,31 @@
   const OverflowingBinaryOperator *OBO =
     cast<OverflowingBinaryOperator>(NarrowUse);
   ExtendKind ExtKind = getExtendKind(NarrowDef);
+  const Instruction *Context = nullptr;
+  // Check that all uses are either s/zext, or narrow def (in case of we are
+  // widening the IV increment).
+  for (Use &U : NarrowUse->uses()) {
+    if (U.getUser() == NarrowDef)
+      continue;
+    Instruction *User = nullptr;
+    if (ExtKind == SignExtended)
+      User = dyn_cast<SExtInst>(U.getUser());
+    else
+      User = dyn_cast<ZExtInst>(U.getUser());
+    if (!User || User->getType() != WideType)
+      return false;
+    if (!Context)
+      // Pick first user as context.
+      Context = User;
+    else if (DT->dominates(User, Context))
+      Context = User;
+    else if (!DT->dominates(Context, User))
+      // For users that don't have dominance relation, use common dominator.
+      Context =
+          DT->findNearestCommonDominator(Context->getParent(),
+                                         User->getParent())->getTerminator();
+  }
+
   bool CanSignExtend = ExtKind == SignExtended && OBO->hasNoSignedWrap();
   bool CanZeroExtend = ExtKind == ZeroExtended && OBO->hasNoUnsignedWrap();
   auto AnotherOpExtKind = ExtKind;
@@ -1136,8 +1161,8 @@
     auto GEPred = ICmpInst::ICMP_UGE;
     if (!SE->isKnownNegative(RHS))
       return false;
-    bool ProvedSubNUW = SE->isKnownPredicateAt(
-        GEPred, LHS, SE->getNegativeSCEV(RHS), NarrowUse);
+    bool ProvedSubNUW =
+        SE->isKnownPredicateAt(GEPred, LHS, SE->getNegativeSCEV(RHS), Context);
     if (!ProvedSubNUW)
       return false;
     // In fact, our 'add' is 'sub nuw'. We will need to widen the 2nd operand as
@@ -1151,20 +1176,6 @@
   if (!AddRecOp1 || AddRecOp1->getLoop() != L)
     return false;
 
-  // Check that all uses are either s/zext, or narrow def (in case of we are
-  // widening the IV increment).
-  for (Use &U : NarrowUse->uses()) {
-    if (U.getUser() == NarrowDef)
-      continue;
-    Instruction *User = nullptr;
-    if (ExtKind == SignExtended)
-      User = dyn_cast<SExtInst>(U.getUser());
-    else
-      User = dyn_cast<ZExtInst>(U.getUser());
-    if (!User || User->getType() != WideType)
-      return false;
-  }
-
   LLVM_DEBUG(dbgs() << "Cloning arithmetic IVUser: " << *NarrowUse << "\n");
 
   // Generating a widening use instruction.
Index: llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
+++ llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
@@ -545,8 +545,6 @@
   ret i32 22
 }
 
-; TODO: We don't really need trunc/zext here because when iv.next overflows,
-; its value is not used.
 define i32 @test11(i32 %start, i32* %p, i32* %q) {
 ; CHECK-LABEL: @test11(
 ; CHECK-NEXT:  entry:
@@ -554,16 +552,13 @@
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[BACKEDGE:%.*]] ], [ [[TMP0]], [[ENTRY:%.*]] ]
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[INDVARS_IV]] to i32
-; CHECK-NEXT:    [[IV_NEXT:%.*]] = add i32 [[TMP1]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i64 [[INDVARS_IV]], -1
 ; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[INDVARS_IV]], 0
 ; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[BACKEDGE]]
 ; CHECK:       backedge:
-; CHECK-NEXT:    [[INDEX:%.*]] = zext i32 [[IV_NEXT]] to i64
-; CHECK-NEXT:    [[STORE_ADDR:%.*]] = getelementptr i32, i32* [[P:%.*]], i64 [[INDEX]]
+; CHECK-NEXT:    [[STORE_ADDR:%.*]] = getelementptr i32, i32* [[P:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    store i32 1, i32* [[STORE_ADDR]], align 4
-; CHECK-NEXT:    [[LOAD_ADDR:%.*]] = getelementptr i32, i32* [[Q:%.*]], i64 [[INDEX]]
-; CHECK-NEXT:    [[STOP:%.*]] = load i32, i32* [[Q]], align 4
+; CHECK-NEXT:    [[STOP:%.*]] = load i32, i32* [[Q:%.*]], align 4
 ; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp eq i32 [[STOP]], 0
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
 ; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[FAILURE:%.*]]