path: root/lib/CodeGen/MachineLICM.cpp

//===-- MachineLICM.cpp - Machine Loop Invariant Code Motion Pass ---------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs loop invariant code motion on machine instructions. We
// attempt to remove as much code from the body of a loop as possible.
//
// This pass does not attempt to throttle itself to limit register pressure.
// The register allocation phases are expected to perform rematerialization
// to recover when register pressure is high.
//
// This pass is not intended to be a replacement or a complete alternative
// for the LLVM-IR-level LICM pass. It is only designed to hoist simple
// constructs that are not exposed before lowering and instruction selection.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "machine-licm"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

static cl::opt<bool>
AvoidSpeculation("avoid-speculation",
                 cl::desc("MachineLICM should avoid speculation"),
                 cl::init(true), cl::Hidden);

STATISTIC(NumHoisted,
          "Number of machine instructions hoisted out of loops");
STATISTIC(NumLowRP,
          "Number of instructions hoisted in low reg pressure situation");
STATISTIC(NumHighLatency,
          "Number of high latency instructions hoisted");
STATISTIC(NumCSEed,
          "Number of hoisted machine instructions CSEed");
STATISTIC(NumPostRAHoisted,
          "Number of machine instructions hoisted out of loops post regalloc");

namespace {
  class MachineLICM : public MachineFunctionPass {
    bool PreRegAlloc;

    const TargetMachine   *TM;
    const TargetInstrInfo *TII;
    const TargetLowering *TLI;
    const TargetRegisterInfo *TRI;
    const MachineFrameInfo *MFI;
    MachineRegisterInfo *MRI;
    const InstrItineraryData *InstrItins;

    // Various analyses that we use...
    AliasAnalysis        *AA;      // Alias analysis info.
    MachineLoopInfo      *MLI;     // Current MachineLoopInfo
    MachineDominatorTree *DT;      // Machine dominator tree for the cur loop

    // State that is updated as we process loops
    bool         Changed;          // True if a loop is changed.
    bool         FirstInLoop;      // True if it's the first LICM in the loop.
    MachineLoop *CurLoop;          // The current loop we are working on.
    MachineBasicBlock *CurPreheader;