llvm/lib/CodeGen/TailDuplication.cpp

//===- TailDuplication.cpp - Duplicate blocks into predecessors' tails ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass duplicates basic blocks ending in unconditional branches into
// the tails of their predecessors, using the TailDuplicator utility class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TailDuplicator.h"
#include "llvm/Pass.h"

using namespace llvm;

#define DEBUG_TYPE "tailduplication"

namespace {

/// Perform tail duplication. Delegates to TailDuplicator
class TailDuplicatePass : public MachineFunctionPass {
  TailDuplicator Duplicator;

public:
  static char ID;

  explicit TailDuplicatePass() : MachineFunctionPass(ID) {}

  bool runOnMachineFunction(MachineFunction &MF) override;

  void getAnalysisUsage(AnalysisUsage &AU) const override;
};

} // end anonymous namespace

char TailDuplicatePass::ID = 0;

char &llvm::TailDuplicateID = TailDuplicatePass::ID;

INITIALIZE_PASS(TailDuplicatePass, DEBUG_TYPE, "Tail Duplication", false, false)

bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
  if (skipFunction(MF.getFunction()))
    return false;

  auto MBPI = &getAnalysis<MachineBranchProbabilityInfo>();

  // TODO: Querying isSSA() to determine pre-/post-regalloc is fragile, better
  // split this into two passes instead.
  bool PreRegAlloc = MF.getRegInfo().isSSA();
  Duplicator.initMF(MF, PreRegAlloc, MBPI, /* LayoutMode */ false);

  bool MadeChange = false;
  while (Duplicator.tailDuplicateBlocks())
    MadeChange = true;

  return MadeChange;
}

void TailDuplicatePass::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<MachineBranchProbabilityInfo>();
  MachineFunctionPass::getAnalysisUsage(AU);
}