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diff --git a/llvm/lib/CodeGen/PostRAHazardRecognizer.cpp b/llvm/lib/CodeGen/PostRAHazardRecognizer.cpp
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+++ b/llvm/lib/CodeGen/PostRAHazardRecognizer.cpp
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+//===----- PostRAHazardRecognizer.cpp - hazard recognizer -----------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// This runs the hazard recognizer and emits noops when necessary.  This
+/// gives targets a way to run the hazard recognizer without running one of
+/// the schedulers.  Example use cases for this pass would be:
+///
+/// - Targets that need the hazard recognizer to be run at -O0.
+/// - Targets that want to guarantee that hazards at the beginning of
+///   scheduling regions are handled correctly.  The post-RA scheduler is
+///   a top-down scheduler, but when there are multiple scheduling regions
+///   in a basic block, it visits the regions in bottom-up order.  This
+///   makes it impossible for the scheduler to gauranttee it can correctly
+///   handle hazards at the beginning of scheduling regions.
+///
+/// This pass traverses all the instructions in a program in top-down order.
+/// In contrast to the instruction scheduling passes, this pass never resets
+/// the hazard recognizer to ensure it can correctly handles noop hazards at
+/// the beginning of blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "post-RA-hazard-rec"
+
+STATISTIC(NumNoops, "Number of noops inserted");
+
+namespace {
+  class PostRAHazardRecognizer : public MachineFunctionPass {
+
+  public:
+    static char ID;
+    PostRAHazardRecognizer() : MachineFunctionPass(ID) {}
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.setPreservesCFG();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+
+    bool runOnMachineFunction(MachineFunction &Fn) override;
+
+  };
+  char PostRAHazardRecognizer::ID = 0;
+
+}
+
+char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizer::ID;
+
+INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE,
+                "Post RA hazard recognizer", false, false)
+
+bool PostRAHazardRecognizer::runOnMachineFunction(MachineFunction &Fn) {
+  const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
+  std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
+      TII->CreateTargetPostRAHazardRecognizer(Fn));
+
+  // Return if the target has not implemented a hazard recognizer.
+  if (!HazardRec.get())
+    return false;
+
+  // Loop over all of the basic blocks
+  for (auto &MBB : Fn) {
+    // We do not call HazardRec->reset() here to make sure we are handling noop
+    // hazards at the start of basic blocks.
+    for (MachineInstr &MI : MBB) {
+      // If we need to emit noops prior to this instruction, then do so.
+      unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);
+      for (unsigned i = 0; i != NumPreNoops; ++i) {
+        HazardRec->EmitNoop();
+        TII->insertNoop(MBB, MachineBasicBlock::iterator(MI));
+        ++NumNoops;
+      }
+
+      HazardRec->EmitInstruction(&MI);
+      if (HazardRec->atIssueLimit()) {
+        HazardRec->AdvanceCycle();
+      }
+    }
+  }
+  return true;
+}