PreAllocSplitting.cpp

//===-- PreAllocSplitting.cpp - Pre-allocation Interval Spltting Pass. ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level pre-register allocation
// live interval splitting pass. It finds live interval barriers, i.e.
// instructions which will kill all physical registers in certain register
// classes, and split all live intervals which cross the barrier.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "pre-alloc-split"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;

static cl::opt<int> PreSplitLimit("pre-split-limit", cl::init(-1), cl::Hidden);

STATISTIC(NumSplits, "Number of intervals split");
STATISTIC(NumRemats, "Number of intervals split by rematerialization");

namespace {
  class VISIBILITY_HIDDEN PreAllocSplitting : public MachineFunctionPass {
    MachineFunction       *CurrMF;
    const TargetMachine   *TM;
    const TargetInstrInfo *TII;
    MachineFrameInfo      *MFI;
    MachineRegisterInfo   *MRI;
    LiveIntervals         *LIs;
    LiveStacks            *LSs;

    // Barrier - Current barrier being processed.
    MachineInstr          *Barrier;

    // BarrierMBB - Basic block where the barrier resides in.
    MachineBasicBlock     *BarrierMBB;

    // Barrier - Current barrier index.
    unsigned              BarrierIdx;

    // CurrLI - Current live interval being split.
    LiveInterval          *CurrLI;

    // CurrSLI - Current stack slot live interval.
    LiveInterval          *CurrSLI;

    // CurrSValNo - Current val# for the stack slot live interval.
    VNInfo                *CurrSValNo;

    // IntervalSSMap - A map from live interval to spill slots.
    DenseMap<unsigned, int> IntervalSSMap;

    // Def2SpillMap - A map from a def instruction index to spill index.
    DenseMap<unsigned, unsigned> Def2SpillMap;

  public:
    static char ID;
    PreAllocSplitting() : MachineFunctionPass(&ID) {}

    virtual bool runOnMachineFunction(MachineFunction &MF);

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<LiveIntervals>();
      AU.addPreserved<LiveIntervals>();
      AU.addRequired<LiveStacks>();
      AU.addPreserved<LiveStacks>();
      AU.addPreserved<RegisterCoalescer>();
      if (StrongPHIElim)
        AU.addPreservedID(StrongPHIEliminationID);
      else
        AU.addPreservedID(PHIEliminationID);
      AU.addRequired<MachineDominatorTree>();
      AU.addRequired<MachineLoopInfo>();
      AU.addPreserved<MachineDominatorTree>();
      AU.addPreserved<MachineLoopInfo>();
      MachineFunctionPass::getAnalysisUsage(AU);
    }
    
    virtual void releaseMemory() {
      IntervalSSMap.clear();
      Def2SpillMap.clear();
    }

    virtual const char *getPassName() const {
      return "Pre-Register Allocaton Live Interval Splitting";
    }

    /// print - Implement the dump method.
    virtual void print(std::ostream &O, const Module* M = 0) const {
      LIs->print(O, M);
    }

    void print(std::ostream *O, const Module* M = 0) const {
      if (O) print(*O, M);
    }

  private:
    MachineBasicBlock::iterator
      findNextEmptySlot(MachineBasicBlock*, MachineInstr*,
                        unsigned&);

    MachineBasicBlock::iterator
      findSpillPoint(MachineBasicBlock*, MachineInstr*, MachineInstr*,
                     SmallPtrSet<MachineInstr*, 4>&, unsigned&);

    MachineBasicBlock::iterator
      findRestorePoint(MachineBasicBlock*, MachineInstr*, unsigned,
                     SmallPtrSet<MachineInstr*, 4>&, unsigned&);

    int CreateSpillStackSlot(unsigned, const TargetRegisterClass *);

    bool IsAvailableInStack(MachineBasicBlock*, unsigned, unsigned, unsigned,
                            unsigned&, int&) const;

    void UpdateSpillSlotInterval(VNInfo*, unsigned, unsigned);

    void UpdateRegisterInterval(VNInfo*, unsigned, unsigned);

    bool ShrinkWrapToLastUse(MachineBasicBlock*, VNInfo*,
                             SmallVector<MachineOperand*, 4>&,
                             SmallPtrSet<MachineInstr*, 4>&);

    void ShrinkWrapLiveInterval(VNInfo*, MachineBasicBlock*, MachineBasicBlock*,
                        MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*, 8>&,
                DenseMap<MachineBasicBlock*, SmallVector<MachineOperand*, 4> >&,
                  DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 4> >&,
                                SmallVector<MachineBasicBlock*, 4>&);

    bool SplitRegLiveInterval(LiveInterval*);

    bool SplitRegLiveIntervals(const TargetRegisterClass **);
    
    bool createsNewJoin(LiveRange* LR, MachineBasicBlock* DefMBB,
                        MachineBasicBlock* BarrierMBB);
    bool Rematerialize(unsigned vreg, VNInfo* ValNo,
                       MachineInstr* DefMI,
                       MachineBasicBlock::iterator RestorePt,
                       unsigned RestoreIdx,
                       SmallPtrSet<MachineInstr*, 4>& RefsInMBB);
  };
} // end anonymous namespace

char PreAllocSplitting::ID = 0;

static RegisterPass<PreAllocSplitting>
X("pre-alloc-splitting", "Pre-Register Allocation Live Interval Splitting");

const PassInfo *const llvm::PreAllocSplittingID = &X;


/// findNextEmptySlot - Find a gap after the given machine instruction in the
/// instruction index map. If there isn't one, return end().
MachineBasicBlock::iterator
PreAllocSplitting::findNextEmptySlot(MachineBasicBlock *MBB, MachineInstr *MI,
                                     unsigned &SpotIndex) {
  MachineBasicBlock::iterator MII = MI;
  if (++MII != MBB->end()) {
    unsigned Index = LIs->findGapBeforeInstr(LIs->getInstructionIndex(MII));
    if (Index) {
      SpotIndex = Index;
      return MII;
    }
  }
  return MBB->end();
}

/// findSpillPoint - Find a gap as far away from the given MI that's suitable
/// for spilling the current live interval. The index must be before any
/// defs and uses of the live interval register in the mbb. Return begin() if
/// none is found.
MachineBasicBlock::iterator
PreAllocSplitting::findSpillPoint(MachineBasicBlock *MBB, MachineInstr *MI,
                                  MachineInstr *DefMI,
                                  SmallPtrSet<MachineInstr*, 4> &RefsInMBB,
                                  unsigned &SpillIndex) {
  MachineBasicBlock::iterator Pt = MBB->begin();

  // Go top down if RefsInMBB is empty.