Index: include/llvm/Analysis/LoopPass.h
===================================================================
--- include/llvm/Analysis/LoopPass.h
+++ include/llvm/Analysis/LoopPass.h
@@ -155,6 +155,22 @@
   Loop *CurrentLoop;
 };
 
+// This pass is required by the LCSSA transformation. It is used inside
+// LPPassManager to check if current pass preserves lcssa form, and if it does
+// pass manager calls lcssa verification for the current loop.
+struct LCSSAVerificationPass : public FunctionPass {
+  static char ID;
+  LCSSAVerificationPass() : FunctionPass(ID) {
+    initializeLCSSAVerificationPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override { return false; }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesAll();
+  }
+};
+
 } // End llvm namespace
 
 #endif
Index: include/llvm/InitializePasses.h
===================================================================
--- include/llvm/InitializePasses.h
+++ include/llvm/InitializePasses.h
@@ -167,7 +167,8 @@
 void initializeIntervalPartitionPass(PassRegistry&);
 void initializeJumpThreadingPass(PassRegistry&);
 void initializeLCSSAWrapperPassPass(PassRegistry &);
-void initializeLegacyLICMPassPass(PassRegistry&);
+void initializeLCSSAVerificationPassPass(PassRegistry &);
+void initializeLegacyLICMPassPass(PassRegistry &);
 void initializeLazyBranchProbabilityInfoPassPass(PassRegistry&);
 void initializeLazyBlockFrequencyInfoPassPass(PassRegistry&);
 void initializeLazyValueInfoWrapperPassPass(PassRegistry&);
Index: lib/Analysis/Analysis.cpp
===================================================================
--- lib/Analysis/Analysis.cpp
+++ lib/Analysis/Analysis.cpp
@@ -77,6 +77,7 @@
   initializeTargetTransformInfoWrapperPassPass(Registry);
   initializeTypeBasedAAWrapperPassPass(Registry);
   initializeScopedNoAliasAAWrapperPassPass(Registry);
+  initializeLCSSAVerificationPassPass(Registry);
 }
 
 void LLVMInitializeAnalysis(LLVMPassRegistryRef R) {
Index: lib/Analysis/LoopPass.cpp
===================================================================
--- lib/Analysis/LoopPass.cpp
+++ lib/Analysis/LoopPass.cpp
@@ -15,6 +15,7 @@
 
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/LoopPassManager.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRPrintingPasses.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/OptBisect.h"
@@ -140,6 +141,7 @@
   // LPPassManager needs LoopInfo. In the long term LoopInfo class will
   // become part of LPPassManager.
   Info.addRequired<LoopInfoWrapperPass>();
+  Info.addRequired<DominatorTreeWrapperPass>();
   Info.setPreservesAll();
 }
 
@@ -148,6 +150,7 @@
 bool LPPassManager::runOnFunction(Function &F) {
   auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
   LI = &LIWP.getLoopInfo();
+  DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   bool Changed = false;
 
   // Collect inherited analysis from Module level pass manager.
@@ -218,6 +221,12 @@
           TimeRegion PassTimer(getPassTimer(&LIWP));
           CurrentLoop->verifyLoop();
         }
+        // Here we apply same reasoning as in the above case. Only difference
+        // is that LPPassManager might run passes which do not require LCSSA
+        // form (LoopPassPrinter for example). We should skip verification for
+        // such passes.
+        if (mustPreserveAnalysisID(LCSSAVerificationPass::ID))
+          CurrentLoop->isRecursivelyLCSSAForm(*DT, *LI);
 
         // Then call the regular verifyAnalysis functions.
         verifyPreservedAnalysis(P);
@@ -353,3 +362,8 @@
   }
   return false;
 }
+
+char LCSSAVerificationPass::ID = 0;
+INITIALIZE_PASS(LCSSAVerificationPass, "lcssa-verification", "LCSSA Verifier",
+                false, false)
+
Index: lib/Transforms/Utils/LCSSA.cpp
===================================================================
--- lib/Transforms/Utils/LCSSA.cpp
+++ lib/Transforms/Utils/LCSSA.cpp
@@ -51,6 +51,15 @@
 
 STATISTIC(NumLCSSA, "Number of live out of a loop variables");
 
+#ifdef EXPENSIVE_CHECKS
+static bool VerifyLoopLCSSA = true;
+#else
+static bool VerifyLoopLCSSA = false;
+#endif
+static cl::opt<bool,true>
+VerifyLoopLCSSAFlag("verify-loop-lcssa", cl::location(VerifyLoopLCSSA),
+                    cl::desc("Verify loop lcssa form (time consuming)"));
+
 /// Return true if the specified block is in the list.
 static bool isExitBlock(BasicBlock *BB,
                         const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
@@ -322,10 +331,17 @@
 
   bool runOnFunction(Function &F) override;
   void verifyAnalysis() const override {
-    assert(
-        all_of(*LI,
-               [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); }) &&
-        "LCSSA form is broken!");
+    // This check is very expensive. On the loop intensive compiles it may cause
+    // up to 10x slowdown. Currently it's disabled by default. LPPassManager
+    // always does limited form of the lcssa verification. Similar reasoning
+    // was used for the LoopInfo verifier.
+    if (VerifyLoopLCSSA) {
+      assert(all_of(*LI,
+                    [&](Loop *L) {
+                      return L->isRecursivelyLCSSAForm(*DT, *LI);
+                    }) &&
+             "LCSSA form is broken!");
+    }
   };
 
   /// This transformation requires natural loop information & requires that
@@ -342,6 +358,10 @@
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<ScalarEvolutionWrapperPass>();
     AU.addPreserved<SCEVAAWrapperPass>();
+
+    // This is needed to perform LCSSA verification inside LPPassManager
+    AU.addRequired<LCSSAVerificationPass>();
+    AU.addPreserved<LCSSAVerificationPass>();
   }
 };
 }
@@ -351,6 +371,7 @@
                       false, false)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LCSSAVerificationPass)
 INITIALIZE_PASS_END(LCSSAWrapperPass, "lcssa", "Loop-Closed SSA Form Pass",
                     false, false)
 
Index: lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- lib/Transforms/Utils/LoopUtils.cpp
+++ lib/Transforms/Utils/LoopUtils.cpp
@@ -17,6 +17,7 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/Analysis/ScalarEvolutionExpander.h"
@@ -946,6 +947,10 @@
   AU.addPreservedID(LoopSimplifyID);
   AU.addRequiredID(LCSSAID);
   AU.addPreservedID(LCSSAID);
+  // This is used in the LPPassManager to perform LCSSA verification on passes
+  // which preserve lcssa form
+  AU.addRequired<LCSSAVerificationPass>();
+  AU.addPreserved<LCSSAVerificationPass>();
 
   // Loop passes are designed to run inside of a loop pass manager which means
   // that any function analyses they require must be required by the first loop