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diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
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+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
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+//===- LoopDeletion.cpp - Dead Loop Deletion Pass ---------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Dead Loop Deletion Pass. This pass is responsible
+// for eliminating loops with non-infinite computable trip counts that have no
+// side effects or volatile instructions, and do not contribute to the
+// computation of the function's return value.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/LoopDeletion.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Scalar/LoopPassManager.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-delete"
+
+STATISTIC(NumDeleted, "Number of loops deleted");
+
+enum class LoopDeletionResult {
+  Unmodified,
+  Modified,
+  Deleted,
+};
+
+/// Determines if a loop is dead.
+///
+/// This assumes that we've already checked for unique exit and exiting blocks,
+/// and that the code is in LCSSA form.
+static bool isLoopDead(Loop *L, ScalarEvolution &SE,
+                       SmallVectorImpl<BasicBlock *> &ExitingBlocks,
+                       BasicBlock *ExitBlock, bool &Changed,
+                       BasicBlock *Preheader) {
+  // Make sure that all PHI entries coming from the loop are loop invariant.
+  // Because the code is in LCSSA form, any values used outside of the loop
+  // must pass through a PHI in the exit block, meaning that this check is
+  // sufficient to guarantee that no loop-variant values are used outside
+  // of the loop.
+  bool AllEntriesInvariant = true;
+  bool AllOutgoingValuesSame = true;
+  for (PHINode &P : ExitBlock->phis()) {
+    Value *incoming = P.getIncomingValueForBlock(ExitingBlocks[0]);
+
+    // Make sure all exiting blocks produce the same incoming value for the exit
+    // block.  If there are different incoming values for different exiting
+    // blocks, then it is impossible to statically determine which value should
+    // be used.
+    AllOutgoingValuesSame =
+        all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
+          return incoming == P.getIncomingValueForBlock(BB);
+        });
+
+    if (!AllOutgoingValuesSame)
+      break;
+
+    if (Instruction *I = dyn_cast<Instruction>(incoming))
+      if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
+        AllEntriesInvariant = false;
+        break;
+      }
+  }
+
+  if (Changed)
+    SE.forgetLoopDispositions(L);
+
+  if (!AllEntriesInvariant || !AllOutgoingValuesSame)
+    return false;
+
+  // Make sure that no instructions in the block have potential side-effects.
+  // This includes instructions that could write to memory, and loads that are
+  // marked volatile.
+  for (auto &I : L->blocks())
+    if (any_of(*I, [](Instruction &I) { return I.mayHaveSideEffects(); }))
+      return false;
+  return true;
+}
+
+/// This function returns true if there is no viable path from the
+/// entry block to the header of \p L. Right now, it only does
+/// a local search to save compile time.
+static bool isLoopNeverExecuted(Loop *L) {
+  using namespace PatternMatch;
+
+  auto *Preheader = L->getLoopPreheader();
+  // TODO: We can relax this constraint, since we just need a loop
+  // predecessor.
+  assert(Preheader && "Needs preheader!");
+
+  if (Preheader == &Preheader->getParent()->getEntryBlock())
+    return false;
+  // All predecessors of the preheader should have a constant conditional
+  // branch, with the loop's preheader as not-taken.
+  for (auto *Pred: predecessors(Preheader)) {
+    BasicBlock *Taken, *NotTaken;
+    ConstantInt *Cond;
+    if (!match(Pred->getTerminator(),
+               m_Br(m_ConstantInt(Cond), Taken, NotTaken)))
+      return false;
+    if (!Cond->getZExtValue())
+      std::swap(Taken, NotTaken);
+    if (Taken == Preheader)
+      return false;
+  }
+  assert(!pred_empty(Preheader) &&
+         "Preheader should have predecessors at this point!");
+  // All the predecessors have the loop preheader as not-taken target.
+  return true;
+}
+
+/// Remove a loop if it is dead.
+///
+/// A loop is considered dead if it does not impact the observable behavior of
+/// the program other than finite running time. This never removes a loop that
+/// might be infinite (unless it is never executed), as doing so could change
+/// the halting/non-halting nature of a program.
+///
+/// This entire process relies pretty heavily on LoopSimplify form and LCSSA in
+/// order to make various safety checks work.
+///
+/// \returns true if any changes were made. This may mutate the loop even if it
+/// is unable to delete it due to hoisting trivially loop invariant
+/// instructions out of the loop.
+static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
+                                           ScalarEvolution &SE, LoopInfo &LI) {
+  assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
+
+  // We can only remove the loop if there is a preheader that we can branch from
+  // after removing it. Also, if LoopSimplify form is not available, stay out
+  // of trouble.
+  BasicBlock *Preheader = L->getLoopPreheader();
+  if (!Preheader || !L->hasDedicatedExits()) {
+    LLVM_DEBUG(
+        dbgs()
+        << "Deletion requires Loop with preheader and dedicated exits.\n");
+    return LoopDeletionResult::Unmodified;
+  }
+  // We can't remove loops that contain subloops.  If the subloops were dead,
+  // they would already have been removed in earlier executions of this pass.
+  if (L->begin() != L->end()) {
+    LLVM_DEBUG(dbgs() << "Loop contains subloops.\n");
+    return LoopDeletionResult::Unmodified;
+  }
+
+
+  BasicBlock *ExitBlock = L->getUniqueExitBlock();
+
+  if (ExitBlock && isLoopNeverExecuted(L)) {
+    LLVM_DEBUG(dbgs() << "Loop is proven to never execute, delete it!");
+    // Set incoming value to undef for phi nodes in the exit block.
+    for (PHINode &P : ExitBlock->phis()) {
+      std::fill(P.incoming_values().begin(), P.incoming_values().end(),
+                UndefValue::get(P.getType()));
+    }
+    deleteDeadLoop(L, &DT, &SE, &LI);
+    ++NumDeleted;
+    return LoopDeletionResult::Deleted;
+  }
+
+  // The remaining checks below are for a loop being dead because all statements
+  // in the loop are invariant.
+  SmallVector<BasicBlock *, 4> ExitingBlocks;
+  L->getExitingBlocks(ExitingBlocks);
+
+  // We require that the loop only have a single exit block.  Otherwise, we'd
+  // be in the situation of needing to be able to solve statically which exit
+  // block will be branched to, or trying to preserve the branching logic in
+  // a loop invariant manner.
+  if (!ExitBlock) {
+    LLVM_DEBUG(dbgs() << "Deletion requires single exit block\n");
+    return LoopDeletionResult::Unmodified;
+  }
+  // Finally, we have to check that the loop really is dead.
+  bool Changed = false;
+  if (!isLoopDead(L, SE, ExitingBlocks, ExitBlock, Changed, Preheader)) {
+    LLVM_DEBUG(dbgs() << "Loop is not invariant, cannot delete.\n");
+    return Changed ? LoopDeletionResult::Modified
+                   : LoopDeletionResult::Unmodified;
+  }
+
+  // Don't remove loops for which we can't solve the trip count.
+  // They could be infinite, in which case we'd be changing program behavior.
+  const SCEV *S = SE.getConstantMaxBackedgeTakenCount(L);
+  if (isa<SCEVCouldNotCompute>(S)) {
+    LLVM_DEBUG(dbgs() << "Could not compute SCEV MaxBackedgeTakenCount.\n");
+    return Changed ? LoopDeletionResult::Modified
+                   : LoopDeletionResult::Unmodified;
+  }
+
+  LLVM_DEBUG(dbgs() << "Loop is invariant, delete it!");
+  deleteDeadLoop(L, &DT, &SE, &LI);
+  ++NumDeleted;
+
+  return LoopDeletionResult::Deleted;
+}
+
+PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
+                                        LoopStandardAnalysisResults &AR,
+                                        LPMUpdater &Updater) {
+
+  LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ");
+  LLVM_DEBUG(L.dump());
+  std::string LoopName = L.getName();
+  auto Result = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI);
+  if (Result == LoopDeletionResult::Unmodified)
+    return PreservedAnalyses::all();
+
+  if (Result == LoopDeletionResult::Deleted)
+    Updater.markLoopAsDeleted(L, LoopName);
+
+  return getLoopPassPreservedAnalyses();
+}
+
+namespace {
+class LoopDeletionLegacyPass : public LoopPass {
+public:
+  static char ID; // Pass ID, replacement for typeid
+  LoopDeletionLegacyPass() : LoopPass(ID) {
+    initializeLoopDeletionLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  // Possibly eliminate loop L if it is dead.
+  bool runOnLoop(Loop *L, LPPassManager &) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    getLoopAnalysisUsage(AU);
+  }
+};
+}
+
+char LoopDeletionLegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopDeletionLegacyPass, "loop-deletion",
+                      "Delete dead loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_END(LoopDeletionLegacyPass, "loop-deletion",
+                    "Delete dead loops", false, false)
+
+Pass *llvm::createLoopDeletionPass() { return new LoopDeletionLegacyPass(); }
+
+bool LoopDeletionLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
+  if (skipLoop(L))
+    return false;
+  DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+  LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+
+  LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ");
+  LLVM_DEBUG(L->dump());
+
+  LoopDeletionResult Result = deleteLoopIfDead(L, DT, SE, LI);
+
+  if (Result == LoopDeletionResult::Deleted)
+    LPM.markLoopAsDeleted(*L);
+
+  return Result != LoopDeletionResult::Unmodified;
+}