Index: llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -406,15 +406,32 @@
                                                      DeadLoopBlocks.end());
       MSSAU->removeBlocks(DeadLoopBlocksSet);
     }
+
+    // The function LI.erase has some invariants that need to be preserved when
+    // it tries to remove a loop which is not the top-level loop. In particular,
+    // it requires loop's preheader to be strictly in loop's parent. We cannot
+    // just remove blocks one by one, because after removal of preheader we may
+    // break this invariant for the dead loop. So we detatch and erase all dead
+    // loops beforehand.
+    for (auto *BB : DeadLoopBlocks)
+      if (LI.isLoopHeader(BB)) {
+        assert(LI.getLoopFor(BB) != &L && "Attempt to remove current loop!");
+        Loop *DL = LI.getLoopFor(BB);
+        if (DL->getParentLoop()) {
+          for (auto *PL = DL->getParentLoop(); PL; PL = PL->getParentLoop())
+            for (auto *BB : DL->getBlocks())
+              PL->removeBlockFromLoop(BB);
+          DL->getParentLoop()->removeChildLoop(DL);
+          LI.addTopLevelLoop(DL);
+        }
+        LI.erase(DL);
+      }
+
     for (auto *BB : DeadLoopBlocks) {
       assert(BB != L.getHeader() &&
              "Header of the current loop cannot be dead!");
       LLVM_DEBUG(dbgs() << "Deleting dead loop block " << BB->getName()
                         << "\n");
-      if (LI.isLoopHeader(BB)) {
-        assert(LI.getLoopFor(BB) != &L && "Attempt to remove current loop!");
-        LI.erase(LI.getLoopFor(BB));
-      }
       LI.removeBlock(BB);
     }
 
Index: llvm/trunk/test/Transforms/LoopSimplifyCFG/update_parents.ll
===================================================================
--- llvm/trunk/test/Transforms/LoopSimplifyCFG/update_parents.ll
+++ llvm/trunk/test/Transforms/LoopSimplifyCFG/update_parents.ll
@@ -1,5 +1,4 @@
-; XFAIL: *
-; REQUIRES: asserts
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; 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
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -loop-simplifycfg -enable-mssa-loop-dependency=true -verify-memoryssa -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
@@ -7,8 +6,24 @@
 target triple = "x86_64-unknown-linux-gnu"
 
 define void @test() {
-
 ; CHECK-LABEL: @test(
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1.loopexit:
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB2:%.*]]
+; CHECK:       bb2.loopexit:
+; CHECK-NEXT:    br label [[BB2]]
+; CHECK:       bb2:
+; CHECK-NEXT:    switch i32 0, label [[BB2_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[BB1_LOOPEXIT:%.*]]
+; CHECK-NEXT:    i32 2, label [[BB2_LOOPEXIT:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb2-split:
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb3:
+; CHECK-NEXT:    br label [[BB3]]
+;
 
   br label %bb1
 
@@ -32,8 +47,24 @@
 }
 
 define void @test_many_subloops(i1 %c) {
-
 ; CHECK-LABEL: @test_many_subloops(
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1.loopexit:
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB2:%.*]]
+; CHECK:       bb2.loopexit:
+; CHECK-NEXT:    br label [[BB2]]
+; CHECK:       bb2:
+; CHECK-NEXT:    switch i32 0, label [[BB2_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[BB1_LOOPEXIT:%.*]]
+; CHECK-NEXT:    i32 2, label [[BB2_LOOPEXIT:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       bb2-split:
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb3:
+; CHECK-NEXT:    br label [[BB3]]
+;
 
   br label %bb1