path: root/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.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "tailduplication"
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;

STATISTIC(NumTails     , "Number of tails duplicated");
STATISTIC(NumTailDups  , "Number of tail duplicated blocks");
STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
STATISTIC(NumAddedPHIs , "Number of phis added");

// Heuristic for tail duplication.
static cl::opt<unsigned>
TailDuplicateSize("tail-dup-size",
                  cl::desc("Maximum instructions to consider tail duplicating"),
                  cl::init(2), cl::Hidden);

static cl::opt<bool>
TailDupVerify("tail-dup-verify",
              cl::desc("Verify sanity of PHI instructions during taildup"),
              cl::init(false), cl::Hidden);

static cl::opt<unsigned>
TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);

typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;

namespace {
  /// TailDuplicatePass - Perform tail duplication.
  class TailDuplicatePass : public MachineFunctionPass {
    const TargetInstrInfo *TII;
    const TargetRegisterInfo *TRI;
    MachineModuleInfo *MMI;
    MachineRegisterInfo *MRI;
    OwningPtr<RegScavenger> RS;
    bool PreRegAlloc;

    // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
    SmallVector<unsigned, 16> SSAUpdateVRs;

    // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
    // source virtual registers.
    DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;

  public:
    static char ID;
    explicit TailDuplicatePass() :
      MachineFunctionPass(ID), PreRegAlloc(false) {}

    virtual bool runOnMachineFunction(MachineFunction &MF);

  private:
    void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
                           MachineBasicBlock *BB);
    void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
                    MachineBasicBlock *PredBB,
                    DenseMap<unsigned, unsigned> &LocalVRMap,
                    SmallVector<std::pair<unsigned,unsigned>, 4> &Copies,
                    const DenseSet<unsigned> &UsedByPhi,
                    bool Remove);
    void DuplicateInstruction(MachineInstr *MI,
                              MachineBasicBlock *TailBB,
                              MachineBasicBlock *PredBB,
                              MachineFunction &MF,
                              DenseMap<unsigned, unsigned> &LocalVRMap,
                              const DenseSet<unsigned> &UsedByPhi);
    void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
                              SmallVector<MachineBasicBlock*, 8> &TDBBs,
                              SmallSetVector<MachineBasicBlock*, 8> &Succs);
    bool TailDuplicateBlocks(MachineFunction &MF);
    bool shouldTailDuplicate(const MachineFunction &MF,
                             bool IsSimple, MachineBasicBlock &TailBB);
    bool isSimpleBB(MachineBasicBlock *TailBB);
    bool canCompletelyDuplicateBB(MachineBasicBlock &BB);
    bool duplicateSimpleBB(MachineBasicBlock *TailBB,
                           SmallVector<MachineBasicBlock*, 8> &TDBBs,
                           const DenseSet<unsigned> &RegsUsedByPhi,
                           SmallVector<MachineInstr*, 16> &Copies);
    bool TailDuplicate(MachineBasicBlock *TailBB,
                       bool IsSimple,
                       MachineFunction &MF,
                       SmallVector<MachineBasicBlock*, 8> &TDBBs,
                       SmallVector<MachineInstr*, 16> &Copies);
    bool TailDuplicateAndUpdate(MachineBasicBlock *MBB,
                                bool IsSimple,
                                MachineFunction &MF);

    void RemoveDeadBlock(MachineBasicBlock *MBB);
  };

  char TailDuplicatePass::ID = 0;
}

char &llvm::TailDuplicateID