diff --git a/llvm/include/llvm/Transforms/Scalar.h b/llvm/include/llvm/Transforms/Scalar.h
--- a/llvm/include/llvm/Transforms/Scalar.h
+++ b/llvm/include/llvm/Transforms/Scalar.h
@@ -15,6 +15,7 @@
 #define LLVM_TRANSFORMS_SCALAR_H
 
 #include "llvm/Transforms/Utils/SimplifyCFGOptions.h"
+#include "llvm/Analysis/LoopPass.h"
 #include <functional>
 
 namespace llvm {
@@ -159,7 +160,7 @@
 //
 // LoopFlatten - This pass flattens nested loops into a single loop.
 //
-FunctionPass *createLoopFlattenPass();
+LoopPass *createLoopFlattenPass();
 
 //===----------------------------------------------------------------------===//
 //
diff --git a/llvm/include/llvm/Transforms/Scalar/LoopFlatten.h b/llvm/include/llvm/Transforms/Scalar/LoopFlatten.h
--- a/llvm/include/llvm/Transforms/Scalar/LoopFlatten.h
+++ b/llvm/include/llvm/Transforms/Scalar/LoopFlatten.h
@@ -24,7 +24,8 @@
 public:
   LoopFlattenPass() = default;
 
-  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
+  PreservedAnalyses run(LoopNest &LN, LoopAnalysisManager &LAM,
+                        LoopStandardAnalysisResults &AR, LPMUpdater &U);
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -621,7 +621,7 @@
   FPM.addPass(SimplifyCFGPass());
   FPM.addPass(InstCombinePass());
   if (EnableLoopFlatten)
-    FPM.addPass(LoopFlattenPass());
+    FPM.addPass(createFunctionToLoopPassAdaptor(LoopFlattenPass()));
   // The loop passes in LPM2 (LoopFullUnrollPass) do not preserve MemorySSA.
   // *All* loop passes must preserve it, in order to be able to use it.
   FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM2),
@@ -796,7 +796,7 @@
   FPM.addPass(SimplifyCFGPass());
   FPM.addPass(InstCombinePass());
   if (EnableLoopFlatten)
-    FPM.addPass(LoopFlattenPass());
+    FPM.addPass(createFunctionToLoopPassAdaptor(LoopFlattenPass()));
   // The loop passes in LPM2 (LoopIdiomRecognizePass, IndVarSimplifyPass,
   // LoopDeletionPass and LoopFullUnrollPass) do not preserve MemorySSA.
   // *All* loop passes must preserve it, in order to be able to use it.
@@ -1849,7 +1849,7 @@
 
   // More loops are countable; try to optimize them.
   if (EnableLoopFlatten && Level.getSpeedupLevel() > 1)
-    MainFPM.addPass(LoopFlattenPass());
+    MainFPM.addPass(createFunctionToLoopPassAdaptor(LoopFlattenPass()));
 
   if (EnableConstraintElimination)
     MainFPM.addPass(ConstraintEliminationPass());
diff --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -249,7 +249,6 @@
 FUNCTION_PASS("loop-simplify", LoopSimplifyPass())
 FUNCTION_PASS("loop-sink", LoopSinkPass())
 FUNCTION_PASS("loop-unroll-and-jam", LoopUnrollAndJamPass())
-FUNCTION_PASS("loop-flatten", LoopFlattenPass())
 FUNCTION_PASS("lowerinvoke", LowerInvokePass())
 FUNCTION_PASS("lowerswitch", LowerSwitchPass())
 FUNCTION_PASS("mem2reg", PromotePass())
@@ -396,6 +395,7 @@
 LOOP_PASS("loop-rotate", LoopRotatePass())
 LOOP_PASS("no-op-loop", NoOpLoopPass())
 LOOP_PASS("print", PrintLoopPass(dbgs()))
+LOOP_PASS("loop-flatten", LoopFlattenPass())
 LOOP_PASS("loop-deletion", LoopDeletionPass())
 LOOP_PASS("loop-simplifycfg", LoopSimplifyCFGPass())
 LOOP_PASS("loop-reduce", LoopStrengthReducePass())
diff --git a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
--- a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -28,7 +28,9 @@
 
 #include "llvm/Transforms/Scalar/LoopFlatten.h"
 #include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/LoopAnalysisManager.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -671,13 +673,8 @@
   return Changed;
 }
 
-PreservedAnalyses LoopFlattenPass::run(Function &F,
-                                       FunctionAnalysisManager &AM) {
-  auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
-  auto *LI = &AM.getResult<LoopAnalysis>(F);
-  auto *SE = &AM.getResult<ScalarEvolutionAnalysis>(F);
-  auto *AC = &AM.getResult<AssumptionAnalysis>(F);
-  auto *TTI = &AM.getResult<TargetIRAnalysis>(F);
+PreservedAnalyses LoopFlattenPass::run(LoopNest &LN, LoopAnalysisManager &LAM,
+                                       LoopStandardAnalysisResults &AR, LPMUpdater &U) {
 
   bool Changed = false;
 
@@ -685,15 +682,16 @@
   // in simplified form, and also needs LCSSA. Running
   // this pass will simplify all loops that contain inner loops,
   // regardless of whether anything ends up being flattened.
-  for (const auto &L : *LI) {
+
+  for (const auto &L : LN.getLoops()) {
     if (L->isInnermost())
       continue;
     Changed |=
-        simplifyLoop(L, DT, LI, SE, AC, nullptr, false /* PreserveLCSSA */);
-    Changed |= formLCSSARecursively(*L, *DT, LI, SE);
+        simplifyLoop(L, &AR.DT, &AR.LI, &AR.SE, &AR.AC, nullptr, false /* PreserveSSA */);
+    Changed |= formLCSSARecursively(*L, AR.DT, &AR.LI, &AR.SE);
   }
 
-  Changed |= Flatten(DT, LI, SE, AC, TTI);
+  Changed |= Flatten(&AR.DT, &AR.LI, &AR.SE, &AR.AC, &AR.TTI);
 
   if (!Changed)
     return PreservedAnalyses::all();
@@ -702,15 +700,16 @@
 }
 
 namespace {
-class LoopFlattenLegacyPass : public FunctionPass {
+class LoopFlattenLegacyPass : public LoopPass {
 public:
   static char ID; // Pass ID, replacement for typeid
-  LoopFlattenLegacyPass() : FunctionPass(ID) {
+  LoopFlattenLegacyPass() : LoopPass(ID) {
     initializeLoopFlattenLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   // Possibly flatten loop L into its child.
-  bool runOnFunction(Function &F) override;
+  //bool runOnFunction(Function &F) override;
+  bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     getLoopAnalysisUsage(AU);
@@ -730,9 +729,10 @@
 INITIALIZE_PASS_END(LoopFlattenLegacyPass, "loop-flatten", "Flattens loops",
                     false, false)
 
-FunctionPass *llvm::createLoopFlattenPass() { return new LoopFlattenLegacyPass(); }
+LoopPass *llvm::createLoopFlattenPass() { return new LoopFlattenLegacyPass(); }
 
-bool LoopFlattenLegacyPass::runOnFunction(Function &F) {
+bool LoopFlattenLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
+  Function &F = *L->getHeader()->getParent();
   ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
   LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();