Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -89,6 +89,7 @@
   DominatorTree &DT;
   ScalarEvolution &SE;
   MemorySSAUpdater *MSSAU;
+  DomTreeUpdater DTU;
 
   // Whether or not the current loop has irreducible CFG.
   bool HasIrreducibleCFG = false;
@@ -317,7 +318,6 @@
 
     // Construct split preheader and the dummy switch to thread edges from it to
     // dead exits.
-    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
     BasicBlock *Preheader = L.getLoopPreheader();
     BasicBlock *NewPreheader = Preheader->splitBasicBlock(
         Preheader->getTerminator(),
@@ -387,6 +387,8 @@
         while (FixLCSSALoop->getParentLoop() != StillReachable)
           FixLCSSALoop = FixLCSSALoop->getParentLoop();
         assert(FixLCSSALoop && "Should be a loop!");
+        // We need all DT updates to be done before forming LCSSA.
+        DTU.flush();
         formLCSSARecursively(*FixLCSSALoop, DT, &LI, &SE);
       }
     }
@@ -395,7 +397,6 @@
   /// Delete loop blocks that have become unreachable after folding. Make all
   /// relevant updates to DT and LI.
   void deleteDeadLoopBlocks() {
-    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
     if (MSSAU) {
       SmallPtrSet<BasicBlock *, 8> DeadLoopBlocksSet(DeadLoopBlocks.begin(),
                                                      DeadLoopBlocks.end());
@@ -429,8 +430,6 @@
   /// Constant-fold terminators of blocks acculumated in FoldCandidates into the
   /// unconditional branches.
   void foldTerminators() {
-    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
-
     for (BasicBlock *BB : FoldCandidates) {
       assert(LI.getLoopFor(BB) == &L && "Should be a loop block!");
       BasicBlock *TheOnlySucc = getOnlyLiveSuccessor(BB);
@@ -482,7 +481,8 @@
   ConstantTerminatorFoldingImpl(Loop &L, LoopInfo &LI, DominatorTree &DT,
                                 ScalarEvolution &SE,
                                 MemorySSAUpdater *MSSAU)
-      : L(L), LI(LI), DT(DT), SE(SE), MSSAU(MSSAU) {}
+      : L(L), LI(LI), DT(DT), SE(SE), MSSAU(MSSAU),
+        DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy) {}
   bool run() {
     assert(L.getLoopLatch() && "Should be single latch!");
 
@@ -548,6 +548,7 @@
       deleteDeadLoopBlocks();
     }
 
+    DTU.flush();
 #ifndef NDEBUG
     // Make sure that we have preserved all data structures after the transform.
     DT.verify();
Index: test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
===================================================================
--- test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
+++ test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
@@ -1,5 +1,4 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; XFAIL: *
 ; REQUIRES: asserts
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -loop-simplifycfg -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -passes='require<domtree>,loop(simplify-cfg)' -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
@@ -2584,6 +2583,84 @@
 }
 
 define void @test_crash_01() {
+; CHECK-LABEL: @test_crash_01(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br i1 undef, label [[BB17:%.*]], label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    switch i32 0, label [[BB2_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[BB19:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb2-split:
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb3:
+; CHECK-NEXT:    switch i32 undef, label [[BB16:%.*]] [
+; CHECK-NEXT:    i32 0, label [[BB15:%.*]]
+; CHECK-NEXT:    i32 1, label [[BB14:%.*]]
+; CHECK-NEXT:    i32 2, label [[BB13:%.*]]
+; CHECK-NEXT:    i32 3, label [[BB12:%.*]]
+; CHECK-NEXT:    i32 4, label [[BB11:%.*]]
+; CHECK-NEXT:    i32 5, label [[BB8:%.*]]
+; CHECK-NEXT:    i32 6, label [[BB10:%.*]]
+; CHECK-NEXT:    i32 7, label [[BB9:%.*]]
+; CHECK-NEXT:    i32 8, label [[BB7:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb7:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb8:
+; CHECK-NEXT:    switch i32 undef, label [[BB28:%.*]] [
+; CHECK-NEXT:    i32 0, label [[BB27:%.*]]
+; CHECK-NEXT:    i32 1, label [[BB26:%.*]]
+; CHECK-NEXT:    i32 2, label [[BB23:%.*]]
+; CHECK-NEXT:    i32 3, label [[BB24:%.*]]
+; CHECK-NEXT:    i32 4, label [[BB25:%.*]]
+; CHECK-NEXT:    i32 5, label [[BB29:%.*]]
+; CHECK-NEXT:    i32 6, label [[BB22:%.*]]
+; CHECK-NEXT:    i32 7, label [[BB20:%.*]]
+; CHECK-NEXT:    i32 8, label [[BB21:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb9:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb10:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb11:
+; CHECK-NEXT:    br label [[BB8]]
+; CHECK:       bb12:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb13:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb14:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb15:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb16:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb17:
+; CHECK-NEXT:    ret void
+; CHECK:       bb19:
+; CHECK-NEXT:    ret void
+; CHECK:       bb20:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb21:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb22:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb23:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb24:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb25:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb26:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb27:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb28:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb29:
+; CHECK-NEXT:    br label [[BB3]]
+;
 bb:
   br label %bb1
 
@@ -2598,21 +2675,21 @@
 
 bb4:                                              ; preds = %bb3
   switch i32 0, label %bb5 [
-    i32 1, label %bb19
-    i32 2, label %bb18
+  i32 1, label %bb19
+  i32 2, label %bb18
   ]
 
 bb5:                                              ; preds = %bb4
   switch i32 undef, label %bb16 [
-    i32 0, label %bb15
-    i32 1, label %bb14
-    i32 2, label %bb13
-    i32 3, label %bb12
-    i32 4, label %bb11
-    i32 5, label %bb8
-    i32 6, label %bb10
-    i32 7, label %bb9
-    i32 8, label %bb7
+  i32 0, label %bb15
+  i32 1, label %bb14
+  i32 2, label %bb13
+  i32 3, label %bb12
+  i32 4, label %bb11
+  i32 5, label %bb8
+  i32 6, label %bb10
+  i32 7, label %bb9
+  i32 8, label %bb7
   ]
 
 bb6:                                              ; preds = %bb29, %bb18
@@ -2623,15 +2700,15 @@
 
 bb8:                                              ; preds = %bb11, %bb5
   switch i32 undef, label %bb28 [
-    i32 0, label %bb27
-    i32 1, label %bb26
-    i32 2, label %bb23
-    i32 3, label %bb24
-    i32 4, label %bb25
-    i32 5, label %bb29
-    i32 6, label %bb22
-    i32 7, label %bb20
-    i32 8, label %bb21
+  i32 0, label %bb27
+  i32 1, label %bb26
+  i32 2, label %bb23
+  i32 3, label %bb24
+  i32 4, label %bb25
+  i32 5, label %bb29
+  i32 6, label %bb22
+  i32 7, label %bb20
+  i32 8, label %bb21
   ]
 
 bb9:                                              ; preds = %bb5