[llvm] [Hexagon] Add Hexagon Copy Hoisting pass (PR #89313)

[Krzysztof Parzyszek via llvm-commits]

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+//===--------- HexagonCopyHoisting.cpp - Hexagon Copy Hoisting  ----------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// The purpose of this pass is to move the copy instructions that are
+// present in all the successor of a basic block (BB) to the end of BB.
+//===----------------------------------------------------------------------===//
+
+#include "HexagonTargetMachine.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/CodeGen/LiveInterval.h"
+#include "llvm/CodeGen/LiveIntervals.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "CopyHoist"
+
+using namespace llvm;
+
+static cl::opt<std::string> CPHoistFn("cphoistfn", cl::Hidden, cl::desc(""),
+                                      cl::init(""));
+
+namespace llvm {
+void initializeHexagonCopyHoistingPass(PassRegistry &Registry);
+FunctionPass *createHexagonCopyHoisting();
+} // namespace llvm
+
+namespace {
+
+class HexagonCopyHoisting : public MachineFunctionPass {
+
+public:
+  static char ID;
+  HexagonCopyHoisting() : MachineFunctionPass(ID), MFN(0), MRI(0) {
+    initializeHexagonCopyHoistingPass(*PassRegistry::getPassRegistry());
+  }
+
+  StringRef getPassName() const override { return "Hexagon Copy Hoisting"; }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<SlotIndexes>();
+    AU.addRequired<LiveIntervals>();
+    AU.addPreserved<SlotIndexes>();
+    AU.addPreserved<LiveIntervals>();
+    AU.addRequired<MachineDominatorTree>();
+    AU.addPreserved<MachineDominatorTree>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &Fn) override;
+  void collectCopyInst();
+  void addMItoCopyList(MachineInstr *MI);
+  bool analyzeCopy(MachineBasicBlock *BB);
+  bool isSafetoMove(MachineInstr *CandMI);
+  void moveCopyInstr(MachineBasicBlock *DestBB, StringRef key,
+                     MachineInstr *MI);
+
+  MachineFunction *MFN;
+  MachineRegisterInfo *MRI;
+  StringMap<MachineInstr *> CopyMI;
+  std::vector<StringMap<MachineInstr *>> CopyMIList;
+};
+
+} // namespace
+
+char HexagonCopyHoisting::ID = 0;
+
+namespace llvm {
+char &HexagonCopyHoistingID = HexagonCopyHoisting::ID;
+}
+
+bool HexagonCopyHoisting::runOnMachineFunction(MachineFunction &Fn) {
+
+  if ((CPHoistFn != "") && (CPHoistFn != Fn.getFunction().getName()))
+    return false;
+
+  MFN = &Fn;
+  MRI = &Fn.getRegInfo();
+
+  LLVM_DEBUG(dbgs() << "\nCopy Hoisting:" << "\'" << Fn.getName() << "\'\n");
+
+  CopyMIList.clear();
+  CopyMIList.resize(Fn.getNumBlockIDs());
+
+  // Traverse through all basic blocks and collect copy instructions.
+  collectCopyInst();
+
+  // Traverse through the basic blocks again and move the COPY instructions
+  // that are present in all the successors of BB to BB.
+  bool changed = false;
+  for (auto I = po_begin(&Fn), E = po_end(&Fn); I != E; ++I) {
+    MachineBasicBlock &BB = **I;
+    if (!BB.empty()) {
+      if (BB.pred_size() != 1) //
+        continue;
+      auto &BBCopyInst = CopyMIList[BB.getNumber()];
+      if (BBCopyInst.size() > 0)
+        changed |= analyzeCopy(*BB.pred_begin());
+    }
+  }
+  // Re-compute liveness
+  if (changed) {
+    LiveIntervals &LIS = getAnalysis<LiveIntervals>();
+    SlotIndexes *SI = LIS.getSlotIndexes();
+    SI->releaseMemory();
+    SI->runOnMachineFunction(Fn);
+    LIS.releaseMemory();
+    LIS.runOnMachineFunction(Fn);
+  }
+  return changed;
+}
+
+//===----------------------------------------------------------------------===//
+// Save all COPY instructions for each basic block in CopyMIList vector.
+//===----------------------------------------------------------------------===//
+void HexagonCopyHoisting::collectCopyInst() {
+  for (auto BI = MFN->begin(), BE = MFN->end(); BI != BE; ++BI) {
+    MachineBasicBlock *BB = &*BI;
+#ifndef NDEBUG
+    auto &BBCopyInst = CopyMIList[BB->getNumber()];
+    LLVM_DEBUG(dbgs() << "Visiting BB#" << BB->getNumber() << ":\n");
+#endif
+
+    for (auto MII = BB->begin(), MIE = BB->end(); MII != MIE; ++MII) {
+      MachineInstr *MI = &*MII;
+      if (MI->getOpcode() == TargetOpcode::COPY)
+        addMItoCopyList(MI);
+    }
+    LLVM_DEBUG(dbgs() << "\tNumber of copies: " << BBCopyInst.size() << "\n");
+  }
+}
+
+void HexagonCopyHoisting::addMItoCopyList(MachineInstr *MI) {
+  unsigned BBNum = MI->getParent()->getNumber();
+  auto &BBCopyInst = CopyMIList[BBNum];
+  unsigned DstReg = MI->getOperand(0).getReg();
+  unsigned SrcReg = MI->getOperand(1).getReg();
+
+  if (!Register::isVirtualRegister(DstReg) ||
+      !Register::isVirtualRegister(SrcReg) ||
+      MRI->getRegClass(DstReg) != &Hexagon::IntRegsRegClass ||
+      MRI->getRegClass(SrcReg) != &Hexagon::IntRegsRegClass)
+    return;
+
+  StringRef key;
+  SmallString<256> TmpData("");
+  (void)Twine(Register::virtReg2Index(DstReg)).toStringRef(TmpData);
+  TmpData += '=';
+  key = Twine(Register::virtReg2Index(SrcReg)).toStringRef(TmpData);
+  BBCopyInst[key] = MI;
+#ifndef NDEBUG
+  LLVM_DEBUG(dbgs() << "\tAdding Copy Instr to the list: " << MI << "\n");
+  for (auto II = BBCopyInst.begin(), IE = BBCopyInst.end(); II != IE; ++II) {
+    MachineInstr *TempMI = (*II).getValue();
+    LLVM_DEBUG(dbgs() << "\tIn the list: " << TempMI << "\n");
+  }
+#endif
+}
+
+//===----------------------------------------------------------------------===//
+// Look at the COPY instructions of all the successors of BB. If the same
+// instruction is present in every successor and can be safely moved,
+// pull it into BB.
+//===----------------------------------------------------------------------===//
+bool HexagonCopyHoisting::analyzeCopy(MachineBasicBlock *BB) {
+
+  bool changed = false;
+  if (BB->succ_size() < 2)
+    return false;
+
+  for (auto I = BB->succ_begin(), E = BB->succ_end(); I != E; ++I) {
+    MachineBasicBlock *SB = *I;
+    if (SB->pred_size() != 1 || SB->isEHPad() || SB->hasAddressTaken())
+      return false;
+  }
+
+  auto SuccI = BB->succ_begin(), SuccE = BB->succ_end();
+
+  MachineBasicBlock *SBB1 = *SuccI;
+  ++SuccI;
+  auto &BBCopyInst1 = CopyMIList[SBB1->getNumber()];
+
+  for (auto II = BBCopyInst1.begin(), IE = BBCopyInst1.end(); II != IE; ++II) {
+    StringRef key = (*II).getKeyData();
+    MachineInstr *MI = (*II).getValue();
+    bool IsSafetoMove = true;
+    for (SuccI = BB->succ_begin(); SuccI != SuccE; ++SuccI) {
+      MachineBasicBlock *SuccBB = *SuccI;
+      auto &SuccBBCopyInst = CopyMIList[SuccBB->getNumber()];
+      if (!SuccBBCopyInst.count(key)) {
+        // Same copy not present in this successor
+        IsSafetoMove = false;
+        break;
+      }
+      // If present, make sure that it's safe to pull this copy instruction
+      // into the predecessor.
+      MachineInstr *SuccMI = SuccBBCopyInst[key];
+      if (!isSafetoMove(SuccMI)) {
+        IsSafetoMove = false;
+        break;
+      }
+    }
+    // If we have come this far, this copy instruction can be safely
+    // moved to the predecessor basic block.
+    if (IsSafetoMove) {
+      LLVM_DEBUG(dbgs() << "\t\t Moving instr to BB#" << BB->getNumber() << ": "
+                        << MI << "\n");
+      moveCopyInstr(BB, key, MI);
+      // Add my into BB copyMI list.
+      changed = true;
+    }
+  }
+
+#ifndef NDEBUG
+  auto &BBCopyInst = CopyMIList[BB->getNumber()];
+  for (auto II = BBCopyInst.begin(), IE = BBCopyInst.end(); II != IE; ++II) {
+    MachineInstr *TempMI = (*II).getValue();
+    LLVM_DEBUG(dbgs() << "\tIn the list: " << TempMI << "\n");
+  }
+#endif
+  return changed;
+}
+
+bool HexagonCopyHoisting::isSafetoMove(MachineInstr *CandMI) {
+  // Make sure that it's safe to move this 'copy' instruction to the predecessor
+  // basic block.
+  assert(CandMI->getOperand(0).isReg() && CandMI->getOperand(1).isReg());
+  unsigned DefR = CandMI->getOperand(0).getReg();
+  unsigned UseR = CandMI->getOperand(1).getReg();
----------------
kparzysz wrote:

`Register`

https://github.com/llvm/llvm-project/pull/89313