Index: llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -1542,19 +1542,31 @@
   auto AnotherOpExtKind = ExtKind;
 
   // The facts we are going to prove need to be true at the point that
-  // dominates all users. Find this point while checking the users.
+  // dominates all ext users. Find this point while checking the users.
   const Instruction *Context = nullptr;
-  // Check that all uses are either s/zext, or narrow def (in case of we are
-  // widening the IV increment).
+  // Check that all uses are either:
+  // - s/zext that we plan to get rid of;
+  // - narrow def (in case of we are widening the IV increment);
+  // - LCSSA Phis outside the loop.
   SmallVector<Instruction *, 4> ExtUsers;
+  SmallVector<PHINode *, 4> LCSSAPhiUsers;
   for (Use &U : NarrowUse->uses()) {
-    if (U.getUser() == NarrowDef)
+    Instruction *User = dyn_cast<Instruction>(U.getUser());
+    if (User == NarrowDef)
       continue;
-    Instruction *User = nullptr;
+    if (!L->contains(User)) {
+      auto *LCSSAPhi = cast<PHINode>(User);
+      // Make sure there is only 1 input, so that we don't have to split
+      // critical edges.
+      if (LCSSAPhi->getNumOperands() != 1)
+        return false;
+      LCSSAPhiUsers.push_back(LCSSAPhi);
+      continue;
+    }
     if (ExtKind == SignExtended)
-      User = dyn_cast<SExtInst>(U.getUser());
+      User = dyn_cast<SExtInst>(User);
     else
-      User = dyn_cast<ZExtInst>(U.getUser());
+      User = dyn_cast<ZExtInst>(User);
     if (!User || User->getType() != WideType)
       return false;
     ExtUsers.push_back(User);
@@ -1629,6 +1641,21 @@
     User->replaceAllUsesWith(WideBO);
     DeadInsts.emplace_back(User);
   }
+
+  for (PHINode *User : LCSSAPhiUsers) {
+    assert(User->getNumOperands() == 1 && "Checked before!");
+    Builder.SetInsertPoint(User);
+    auto *WidePN =
+        Builder.CreatePHI(WideBO->getType(), 1, User->getName() + "wide");
+    BasicBlock *LoopExitingBlock = User->getParent()->getSinglePredecessor();
+    assert(LoopExitingBlock && L->contains(LoopExitingBlock) &&
+           "Not a LCSSA Phi?");
+    WidePN->addIncoming(WideBO, LoopExitingBlock);
+    Builder.SetInsertPoint(User->getParent()->getFirstNonPHI());
+    auto *TruncPN = Builder.CreateTrunc(WidePN, User->getType());
+    User->replaceAllUsesWith(TruncPN);
+    DeadInsts.emplace_back(User);
+  }
   return true;
 }
 
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
@@ -697,20 +697,18 @@
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[BACKEDGE:%.*]] ], [ [[TMP0]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[INDVARS_IV]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[INDVARS_IV]] to i32
-; CHECK-NEXT:    [[FOO:%.*]] = add i32 [[TMP1]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i64 [[INDVARS_IV]], -1
 ; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[BACKEDGE]]
 ; CHECK:       backedge:
-; CHECK-NEXT:    [[INDEX:%.*]] = zext i32 [[FOO]] 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:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    ret i32 -1
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 -1 to i32
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ; CHECK:       failure:
 ; CHECK-NEXT:    unreachable
 ;
@@ -750,24 +748,23 @@
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[BACKEDGE:%.*]] ], [ [[TMP0]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[INDVARS_IV]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[INDVARS_IV]] to i32
-; CHECK-NEXT:    [[FOO:%.*]] = add i32 [[TMP1]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i64 [[INDVARS_IV]], -1
 ; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[BACKEDGE]]
 ; CHECK:       backedge:
-; CHECK-NEXT:    [[INDEX:%.*]] = zext i32 [[FOO]] 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:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    call void @use(i32 -1)
-; CHECK-NEXT:    ret i32 -1
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 -1 to i32
+; CHECK-NEXT:    call void @use(i32 [[TMP2]])
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ; CHECK:       failure:
-; CHECK-NEXT:    [[FOO_LCSSA1:%.*]] = phi i32 [ [[FOO]], [[BACKEDGE]] ]
-; CHECK-NEXT:    call void @use(i32 [[FOO_LCSSA1]])
+; CHECK-NEXT:    [[FOO_LCSSA1WIDE:%.*]] = phi i64 [ [[TMP1]], [[BACKEDGE]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[FOO_LCSSA1WIDE]] to i32
+; CHECK-NEXT:    call void @use(i32 [[TMP3]])
 ; CHECK-NEXT:    unreachable
 ;
 entry: