InlineSpiller.cpp

//===-------- InlineSpiller.cpp - Insert spills and restores inline -------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The inline spiller modifies the machine function directly instead of
// inserting spills and restores in VirtRegMap.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "regalloc"
#include "Spiller.h"
#include "LiveRangeEdit.h"
#include "VirtRegMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

STATISTIC(NumSpilledRanges,   "Number of spilled live ranges");
STATISTIC(NumSnippets,        "Number of snippets included in spills");
STATISTIC(NumSpills,          "Number of spills inserted");
STATISTIC(NumReloads,         "Number of reloads inserted");
STATISTIC(NumFolded,          "Number of folded stack accesses");
STATISTIC(NumFoldedLoads,     "Number of folded loads");
STATISTIC(NumRemats,          "Number of rematerialized defs for spilling");
STATISTIC(NumOmitReloadSpill, "Number of omitted spills after reloads");
STATISTIC(NumHoistLocal,      "Number of locally hoisted spills");
STATISTIC(NumHoistGlobal,     "Number of globally hoisted spills");
STATISTIC(NumRedundantSpills, "Number of redundant spills identified");

namespace {
class InlineSpiller : public Spiller {
  MachineFunctionPass &Pass;
  MachineFunction &MF;
  LiveIntervals &LIS;
  LiveStacks &LSS;
  AliasAnalysis *AA;
  MachineDominatorTree &MDT;
  MachineLoopInfo &Loops;
  VirtRegMap &VRM;
  MachineFrameInfo &MFI;
  MachineRegisterInfo &MRI;
  const TargetInstrInfo &TII;
  const TargetRegisterInfo &TRI;

  // Variables that are valid during spill(), but used by multiple methods.
  LiveRangeEdit *Edit;
  LiveInterval *StackInt;
  int StackSlot;
  unsigned Original;

  // All registers to spill to StackSlot, including the main register.
  SmallVector<unsigned, 8> RegsToSpill;

  // All COPY instructions to/from snippets.
  // They are ignored since both operands refer to the same stack slot.
  SmallPtrSet<MachineInstr*, 8> SnippetCopies;

  // Values that failed to remat at some point.
  SmallPtrSet<VNInfo*, 8> UsedValues;

  // Information about a value that was defined by a copy from a sibling
  // register.
  struct SibValueInfo {
    // True when all reaching defs were reloads: No spill is necessary.
    bool AllDefsAreReloads;

    // The preferred register to spill.
    unsigned SpillReg;

    // The value of SpillReg that should be spilled.
    VNInfo *SpillVNI;

    // A defining instruction that is not a sibling copy or a reload, or NULL.
    // This can be used as a template for rematerialization.
    MachineInstr *DefMI;

    SibValueInfo(unsigned Reg, VNInfo *VNI)
      : AllDefsAreReloads(false), SpillReg(Reg), SpillVNI(VNI), DefMI(0) {}
  };

  // Values in RegsToSpill defined by sibling copies.
  typedef DenseMap<VNInfo*, SibValueInfo> SibValueMap;
  SibValueMap SibValues;

  // Dead defs generated during spilling.
  SmallVector<MachineInstr*, 8> DeadDefs;

  ~InlineSpiller() {}

public:
  InlineSpiller(MachineFunctionPass &pass,
                MachineFunction &mf,
                VirtRegMap &vrm)
    : Pass(pass),
      MF(mf),
      LIS(pass.getAnalysis<LiveIntervals>()),
      LSS(pass.getAnalysis<LiveStacks>()),
      AA(&pass.getAnalysis<AliasAnalysis>()),
      MDT(pass.getAnalysis<MachineDominatorTree>()),
      Loops(pass.getAnalysis<MachineLoopInfo>()),
      VRM(vrm),
      MFI(*mf.getFrameInfo()),
      MRI(mf.getRegInfo()),
      TII(*mf.getTarget().getInstrInfo()),
      TRI(*mf.getTarget().getRegisterInfo()) {}

  void spill(LiveRangeEdit &);

private:
  bool isSnippet(const LiveInterval &SnipLI);
  void collectRegsToSpill();

  bool isRegToSpill(unsigned Reg) {
    return std::find(RegsToSpill.begin(),
                     RegsToSpill.end(), Reg) != RegsToSpill.end();
  }

  bool isSibling(unsigned Reg);
  MachineInstr *traceSiblingValue(unsigned, VNInfo*, VNInfo*);
  void analyzeSiblingValues();

  bool hoistSpill(LiveInterval &SpillLI, MachineInstr *CopyMI);
  void eliminateRedundantSpills(LiveInterval &LI, VNInfo *VNI);

  void markValueUsed(LiveInterval*, VNInfo*);
  bool reMaterializeFor(LiveInterval&, MachineBasicBlock::iterator MI);
  void reMaterializeAll();

  bool coalesceStackAccess(MachineInstr *MI, unsigned Reg);
  bool foldMemoryOperand(MachineBasicBlock::iterator MI,
                         const SmallVectorImpl<unsigned> &Ops,
                         MachineInstr *LoadMI = 0);
  void insertReload(LiveInterval &NewLI, SlotIndex,
                    MachineBasicBlock::iterator MI);
  void insertSpill(LiveInterval &NewLI, const LiveInterval &OldLI,
                   SlotIndex, MachineBasicBlock::iterator MI);

  void spillAroundUses(unsigned Reg);
  void spillAll();
};
}

namespace llvm {
Spiller *createInlineSpiller(MachineFunctionPass &pass,
                             MachineFunction &mf,
                             VirtRegMap &vrm) {
  return new InlineSpiller(pass, mf, vrm);
}
}

//===----------------------------------------------------------------------===//
//                                Snippets
//===----------------------------------------------------------------------===//

// When spilling a virtual register, we also spill any snippets it is connected
// to. The snippets are small live ranges that only have a single real use,
// leftovers from live range splitting. Spilling them enables memory operand
// folding or tightens the live range around the single use.
//
// This minimizes register pressure and maximizes the store-to-load distance for
// spill slots which can be important in tight loops.

/// isFullCopyOf - If MI is a COPY to or from Reg, return the other register,
/// otherwise return 0.
static unsigned isFullCopyOf(const MachineInstr *MI, unsigned Reg) {
  if (!MI->isFullCopy())
    return 0;
  if (MI->getOperand(0).getReg() == Reg)
      return MI->getOperand(1).getReg();
  if (MI->getOperand(1).getReg() == Reg)
      return MI->getOperand(0).getReg();
  return 0;
}

/// isSnippet - Identify if a live interval is a snippet that should be spilled.
/// It is assumed that SnipLI is a virtual register with the same original as
/// Edit->getReg().
bool InlineSpiller::isSnippet(const LiveInterval &SnipLI) {
  unsigned Reg = Edit->getReg();

  // A snippet is a tiny live range with only a single instruction using it
  // besides copies to/from Reg or spills/fills. We accept:
  //