Index: include/llvm/Transforms/Utils/BasicBlockUtils.h
===================================================================
--- include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -40,14 +40,18 @@
 class Value;
 
 /// Delete the specified block, which must have no predecessors.
-void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr);
+void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
+                     bool DontDeleteUselessPHIs = false);
 
 /// Delete the specified blocks from \p BB. The set of deleted blocks must have
 /// no predecessors that are not being deleted themselves. \p BBs must have no
 /// duplicating blocks. If there are loops among this set of blocks, all
 /// relevant loop info updates should be done before this function is called.
+/// If \p DontDeleteUselessPHIs is true, one-input Phis in successors of blocks
+/// being deleted will be preserved.
 void DeleteDeadBlocks(SmallVectorImpl <BasicBlock *> &BBs,
-                      DomTreeUpdater *DTU = nullptr);
+                      DomTreeUpdater *DTU = nullptr,
+                      bool DontDeleteUselessPHIs = false);
 
 /// We know that BB has one predecessor. If there are any single-entry PHI nodes
 /// in it, fold them away. This handles the case when all entries to the PHI
Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -422,7 +422,7 @@
       LI.removeBlock(BB);
     }
 
-    DeleteDeadBlocks(DeadLoopBlocks, &DTU);
+    DeleteDeadBlocks(DeadLoopBlocks, &DTU, /*DontDeleteUselessPHIs */ true);
     NumLoopBlocksDeleted += DeadLoopBlocks.size();
   }
 
Index: lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- lib/Transforms/Utils/BasicBlockUtils.cpp
+++ lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -47,13 +47,14 @@
 
 using namespace llvm;
 
-void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU) {
+void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU,
+                           bool DontDeleteUselessPHIs) {
   SmallVector<BasicBlock *, 1> BBs = {BB};
-  DeleteDeadBlocks(BBs, DTU);
+  DeleteDeadBlocks(BBs, DTU, DontDeleteUselessPHIs);
 }
 
 void llvm::DeleteDeadBlocks(SmallVectorImpl <BasicBlock *> &BBs,
-                            DomTreeUpdater *DTU) {
+                            DomTreeUpdater *DTU, bool DontDeleteUselessPHIs) {
 #ifndef NDEBUG
   // Make sure that all predecessors of each dead block is also dead.
   SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
@@ -68,7 +69,7 @@
     // Loop through all of our successors and make sure they know that one
     // of their predecessors is going away.
     for (BasicBlock *Succ : successors(BB)) {
-      Succ->removePredecessor(BB);
+      Succ->removePredecessor(BB, DontDeleteUselessPHIs);
       if (DTU)
         Updates.push_back({DominatorTree::Delete, BB, Succ});
     }
Index: test/Transforms/LoopSimplifyCFG/lcssa.ll
===================================================================
--- test/Transforms/LoopSimplifyCFG/lcssa.ll
+++ test/Transforms/LoopSimplifyCFG/lcssa.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 -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -passes='require<domtree>,loop(simplify-cfg)' -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
@@ -93,8 +92,31 @@
 }
 
 define void @bar() {
-
-; CHECK-LABEL: @bar
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    switch i32 0, label [[BB_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[BB10:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb-split:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    [[TMP:%.*]] = phi i32 [ [[TMP7:%.*]], [[BB6:%.*]] ], [ undef, [[BB_SPLIT]] ]
+; CHECK-NEXT:    switch i32 undef, label [[BB5:%.*]] [
+; CHECK-NEXT:    i32 0, label [[BB6]]
+; CHECK-NEXT:    i32 1, label [[BB8:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb5:
+; CHECK-NEXT:    ret void
+; CHECK:       bb6:
+; CHECK-NEXT:    [[TMP7]] = add i32 undef, 123
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb8:
+; CHECK-NEXT:    [[TMP9:%.*]] = phi i32 [ [[TMP]], [[BB1]] ]
+; CHECK-NEXT:    [[USE:%.*]] = add i32 [[TMP9]], 1
+; CHECK-NEXT:    ret void
+; CHECK:       bb10:
+; CHECK-NEXT:    ret void
+;
 
 bb:
   br label %bb1
@@ -105,8 +127,8 @@
 
 bb2:                                              ; preds = %bb1
   switch i32 undef, label %bb10 [
-    i32 0, label %bb3
-    i32 1, label %bb8
+  i32 0, label %bb3
+  i32 1, label %bb8
   ]
 
 bb3:                                              ; preds = %bb2
@@ -114,8 +136,8 @@
 
 bb4:                                              ; preds = %bb1
   switch i32 undef, label %bb5 [
-    i32 0, label %bb6
-    i32 1, label %bb8
+  i32 0, label %bb6
+  i32 1, label %bb8
   ]
 
 bb5:                                              ; preds = %bb4