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diff --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
new file mode 100644
index 000000000000..7c4fd2d140d3
--- /dev/null
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
@@ -0,0 +1,264 @@
+//===- llvm/CodeGen/GlobalISel/InstructionSelect.cpp - InstructionSelect ---==//
+//
+// 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 file implements the InstructionSelect class.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/CodeGen/GlobalISel/GISelKnownBits.h"
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+#include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/Config/config.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/TargetRegistry.h"
+
+#define DEBUG_TYPE "instruction-select"
+
+using namespace llvm;
+
+#ifdef LLVM_GISEL_COV_PREFIX
+static cl::opt<std::string>
+    CoveragePrefix("gisel-coverage-prefix", cl::init(LLVM_GISEL_COV_PREFIX),
+                   cl::desc("Record GlobalISel rule coverage files of this "
+                            "prefix if instrumentation was generated"));
+#else
+static const std::string CoveragePrefix = "";
+#endif
+
+char InstructionSelect::ID = 0;
+INITIALIZE_PASS_BEGIN(InstructionSelect, DEBUG_TYPE,
+                      "Select target instructions out of generic instructions",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_DEPENDENCY(GISelKnownBitsAnalysis)
+INITIALIZE_PASS_END(InstructionSelect, DEBUG_TYPE,
+                    "Select target instructions out of generic instructions",
+                    false, false)
+
+InstructionSelect::InstructionSelect() : MachineFunctionPass(ID) { }
+
+void InstructionSelect::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<TargetPassConfig>();
+  AU.addRequired<GISelKnownBitsAnalysis>();
+  AU.addPreserved<GISelKnownBitsAnalysis>();
+  getSelectionDAGFallbackAnalysisUsage(AU);
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
+  // If the ISel pipeline failed, do not bother running that pass.
+  if (MF.getProperties().hasProperty(
+          MachineFunctionProperties::Property::FailedISel))
+    return false;
+
+  LLVM_DEBUG(dbgs() << "Selecting function: " << MF.getName() << '\n');
+  GISelKnownBits &KB = getAnalysis<GISelKnownBitsAnalysis>().get(MF);
+
+  const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
+  InstructionSelector *ISel = MF.getSubtarget().getInstructionSelector();
+  CodeGenCoverage CoverageInfo;
+  assert(ISel && "Cannot work without InstructionSelector");
+  ISel->setupMF(MF, KB, CoverageInfo);
+
+  // An optimization remark emitter. Used to report failures.
+  MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
+
+  // FIXME: There are many other MF/MFI fields we need to initialize.
+
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+#ifndef NDEBUG
+  // Check that our input is fully legal: we require the function to have the
+  // Legalized property, so it should be.
+  // FIXME: This should be in the MachineVerifier, as the RegBankSelected
+  // property check already is.
+  if (!DisableGISelLegalityCheck)
+    if (const MachineInstr *MI = machineFunctionIsIllegal(MF)) {
+      reportGISelFailure(MF, TPC, MORE, "gisel-select",
+                         "instruction is not legal", *MI);
+      return false;
+    }
+  // FIXME: We could introduce new blocks and will need to fix the outer loop.
+  // Until then, keep track of the number of blocks to assert that we don't.
+  const size_t NumBlocks = MF.size();
+#endif
+
+  for (MachineBasicBlock *MBB : post_order(&MF)) {
+    if (MBB->empty())
+      continue;
+
+    // Select instructions in reverse block order. We permit erasing so have
+    // to resort to manually iterating and recognizing the begin (rend) case.
+    bool ReachedBegin = false;
+    for (auto MII = std::prev(MBB->end()), Begin = MBB->begin();
+         !ReachedBegin;) {
+#ifndef NDEBUG
+      // Keep track of the insertion range for debug printing.
+      const auto AfterIt = std::next(MII);
+#endif
+      // Select this instruction.
+      MachineInstr &MI = *MII;
+
+      // And have our iterator point to the next instruction, if there is one.
+      if (MII == Begin)
+        ReachedBegin = true;
+      else
+        --MII;
+
+      LLVM_DEBUG(dbgs() << "Selecting: \n  " << MI);
+
+      // We could have folded this instruction away already, making it dead.
+      // If so, erase it.
+      if (isTriviallyDead(MI, MRI)) {
+        LLVM_DEBUG(dbgs() << "Is dead; erasing.\n");
+        MI.eraseFromParentAndMarkDBGValuesForRemoval();
+        continue;
+      }
+
+      if (!ISel->select(MI)) {
+        // FIXME: It would be nice to dump all inserted instructions.  It's
+        // not obvious how, esp. considering select() can insert after MI.
+        reportGISelFailure(MF, TPC, MORE, "gisel-select", "cannot select", MI);
+        return false;
+      }
+
+      // Dump the range of instructions that MI expanded into.
+      LLVM_DEBUG({
+        auto InsertedBegin = ReachedBegin ? MBB->begin() : std::next(MII);
+        dbgs() << "Into:\n";
+        for (auto &InsertedMI : make_range(InsertedBegin, AfterIt))
+          dbgs() << "  " << InsertedMI;
+        dbgs() << '\n';
+      });
+    }
+  }
+
+  for (MachineBasicBlock &MBB : MF) {
+    if (MBB.empty())
+      continue;
+
+    // Try to find redundant copies b/w vregs of the same register class.
+    bool ReachedBegin = false;
+    for (auto MII = std::prev(MBB.end()), Begin = MBB.begin(); !ReachedBegin;) {
+      // Select this instruction.
+      MachineInstr &MI = *MII;
+
+      // And have our iterator point to the next instruction, if there is one.
+      if (MII == Begin)
+        ReachedBegin = true;
+      else
+        --MII;
+      if (MI.getOpcode() != TargetOpcode::COPY)
+        continue;
+      Register SrcReg = MI.getOperand(1).getReg();
+      Register DstReg = MI.getOperand(0).getReg();
+      if (Register::isVirtualRegister(SrcReg) &&
+          Register::isVirtualRegister(DstReg)) {
+        auto SrcRC = MRI.getRegClass(SrcReg);
+        auto DstRC = MRI.getRegClass(DstReg);
+        if (SrcRC == DstRC) {
+          MRI.replaceRegWith(DstReg, SrcReg);
+          MI.eraseFromParentAndMarkDBGValuesForRemoval();
+        }
+      }
+    }
+  }
+
+#ifndef NDEBUG
+  const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
+  // Now that selection is complete, there are no more generic vregs.  Verify
+  // that the size of the now-constrained vreg is unchanged and that it has a
+  // register class.
+  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
+    unsigned VReg = Register::index2VirtReg(I);
+
+    MachineInstr *MI = nullptr;
+    if (!MRI.def_empty(VReg))
+      MI = &*MRI.def_instr_begin(VReg);
+    else if (!MRI.use_empty(VReg))
+      MI = &*MRI.use_instr_begin(VReg);
+    if (!MI)
+      continue;
+
+    const TargetRegisterClass *RC = MRI.getRegClassOrNull(VReg);
+    if (!RC) {
+      reportGISelFailure(MF, TPC, MORE, "gisel-select",
+                         "VReg has no regclass after selection", *MI);
+      return false;
+    }
+
+    const LLT Ty = MRI.getType(VReg);
+    if (Ty.isValid() && Ty.getSizeInBits() > TRI.getRegSizeInBits(*RC)) {
+      reportGISelFailure(
+          MF, TPC, MORE, "gisel-select",
+          "VReg's low-level type and register class have different sizes", *MI);
+      return false;
+    }
+  }
+
+  if (MF.size() != NumBlocks) {
+    MachineOptimizationRemarkMissed R("gisel-select", "GISelFailure",
+                                      MF.getFunction().getSubprogram(),
+                                      /*MBB=*/nullptr);
+    R << "inserting blocks is not supported yet";
+    reportGISelFailure(MF, TPC, MORE, R);
+    return false;
+  }
+#endif
+  auto &TLI = *MF.getSubtarget().getTargetLowering();
+  TLI.finalizeLowering(MF);
+
+  // Determine if there are any calls in this machine function. Ported from
+  // SelectionDAG.
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  for (const auto &MBB : MF) {
+    if (MFI.hasCalls() && MF.hasInlineAsm())
+      break;
+
+    for (const auto &MI : MBB) {
+      if ((MI.isCall() && !MI.isReturn()) || MI.isStackAligningInlineAsm())
+        MFI.setHasCalls(true);
+      if (MI.isInlineAsm())
+        MF.setHasInlineAsm(true);
+    }
+  }
+
+
+  LLVM_DEBUG({
+    dbgs() << "Rules covered by selecting function: " << MF.getName() << ":";
+    for (auto RuleID : CoverageInfo.covered())
+      dbgs() << " id" << RuleID;
+    dbgs() << "\n\n";
+  });
+  CoverageInfo.emit(CoveragePrefix,
+                    MF.getSubtarget()
+                        .getTargetLowering()
+                        ->getTargetMachine()
+                        .getTarget()
+                        .getBackendName());
+
+  // If we successfully selected the function nothing is going to use the vreg
+  // types after us (otherwise MIRPrinter would need them). Make sure the types
+  // disappear.
+  MRI.clearVirtRegTypes();
+
+  // FIXME: Should we accurately track changes?
+  return true;
+}