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llvm-mirror/lib/CodeGen/RegisterScavenging.cpp

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8.9 KiB
C++

//===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the Evan Cheng and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine register scavenger. It can provide
// information such as unused register at any point in a machine basic block.
// It also provides a mechanism to make registers availbale by evicting them
// to spill slots.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "reg-scavenging"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) {
const MachineFunction &MF = *mbb->getParent();
const TargetMachine &TM = MF.getTarget();
TII = TM.getInstrInfo();
RegInfo = TM.getRegisterInfo();
assert((NumPhysRegs == 0 || NumPhysRegs == RegInfo->getNumRegs()) &&
"Target changed?");
if (!MBB) {
NumPhysRegs = RegInfo->getNumRegs();
RegsAvailable.resize(NumPhysRegs);
// Create reserved registers bitvector.
ReservedRegs = RegInfo->getReservedRegs(MF);
// Create callee-saved registers bitvector.
CalleeSavedRegs.resize(NumPhysRegs);
const unsigned *CSRegs = RegInfo->getCalleeSavedRegs();
if (CSRegs != NULL)
for (unsigned i = 0; CSRegs[i]; ++i)
CalleeSavedRegs.set(CSRegs[i]);
}
MBB = mbb;
ScavengedReg = 0;
ScavengedRC = NULL;
// All registers started out unused.
RegsAvailable.set();
// Reserved registers are always used.
RegsAvailable ^= ReservedRegs;
// Live-in registers are in use.
if (!MBB->livein_empty())
for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(),
E = MBB->livein_end(); I != E; ++I)
setUsed(*I);
Tracking = false;
}
void RegScavenger::restoreScavengedReg() {
if (!ScavengedReg)
return;
RegInfo->loadRegFromStackSlot(*MBB, MBBI, ScavengedReg,
ScavengingFrameIndex, ScavengedRC);
MachineBasicBlock::iterator II = prior(MBBI);
RegInfo->eliminateFrameIndex(II, this);
setUsed(ScavengedReg);
ScavengedReg = 0;
ScavengedRC = NULL;
}
void RegScavenger::forward() {
// Move ptr forward.
if (!Tracking) {
MBBI = MBB->begin();
Tracking = true;
} else {
assert(MBBI != MBB->end() && "Already at the end of the basic block!");
MBBI = next(MBBI);
}
MachineInstr *MI = MBBI;
// Reaching a terminator instruction. Restore a scavenged register (which
// must be life out.
if (TII->isTerminatorInstr(MI->getOpcode()))
restoreScavengedReg();
// Process uses first.
BitVector ChangedRegs(NumPhysRegs);
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isUse())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
if (!isUsed(Reg)) {
// Register has been scavenged. Restore it!
if (Reg != ScavengedReg)
assert(false);
else
restoreScavengedReg();
}
if (MO.isKill() && !isReserved(Reg))
ChangedRegs.set(Reg);
}
// Change states of all registers after all the uses are processed to guard
// against multiple uses.
setUnused(ChangedRegs);
// Process defs.
const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
// If it's dead upon def, then it is now free.
if (MO.isDead()) {
setUnused(Reg);
continue;
}
// Skip two-address destination operand.
if (TID->findTiedToSrcOperand(i) != -1) {
assert(isUsed(Reg));
continue;
}
assert(isUnused(Reg) || isReserved(Reg));
setUsed(Reg);
}
}
void RegScavenger::backward() {
assert(Tracking && "Not tracking states!");
assert(MBBI != MBB->begin() && "Already at start of basic block!");
// Move ptr backward.
MBBI = prior(MBBI);
MachineInstr *MI = MBBI;
// Process defs first.
const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
// Skip two-address destination operand.
if (TID->findTiedToSrcOperand(i) != -1)
continue;
unsigned Reg = MO.getReg();
assert(isUsed(Reg));
if (!isReserved(Reg))
setUnused(Reg);
}
// Process uses.
BitVector ChangedRegs(NumPhysRegs);
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isUse())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
assert(isUnused(Reg) || isReserved(Reg));
ChangedRegs.set(Reg);
}
setUsed(ChangedRegs);
}
void RegScavenger::getRegsUsed(BitVector &used, bool includeReserved) {
if (includeReserved)
used = ~RegsAvailable;
else
used = ~RegsAvailable & ~ReservedRegs;
}
/// CreateRegClassMask - Set the bits that represent the registers in the
/// TargetRegisterClass.
static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
++I)
Mask.set(*I);
}
unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
const BitVector &Candidates) const {
// Mask off the registers which are not in the TargetRegisterClass.
BitVector RegsAvailableCopy(NumPhysRegs, false);
CreateRegClassMask(RegClass, RegsAvailableCopy);
RegsAvailableCopy &= RegsAvailable;
// Restrict the search to candidates.
RegsAvailableCopy &= Candidates;
// Returns the first unused (bit is set) register, or 0 is none is found.
int Reg = RegsAvailableCopy.find_first();
return (Reg == -1) ? 0 : Reg;
}
unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
bool ExCalleeSaved) const {
// Mask off the registers which are not in the TargetRegisterClass.
BitVector RegsAvailableCopy(NumPhysRegs, false);
CreateRegClassMask(RegClass, RegsAvailableCopy);
RegsAvailableCopy &= RegsAvailable;
// If looking for a non-callee-saved register, mask off all the callee-saved
// registers.
if (ExCalleeSaved)
RegsAvailableCopy &= ~CalleeSavedRegs;
// Returns the first unused (bit is set) register, or 0 is none is found.
int Reg = RegsAvailableCopy.find_first();
return (Reg == -1) ? 0 : Reg;
}
/// calcDistanceToUse - Calculate the distance to the first use of the
/// specified register.
static unsigned calcDistanceToUse(MachineBasicBlock *MBB,
MachineBasicBlock::iterator I, unsigned Reg) {
unsigned Dist = 0;
I = next(I);
while (I != MBB->end()) {
Dist++;
if (I->findRegisterUseOperandIdx(Reg) != -1)
return Dist;
I = next(I);
}
return Dist + 1;
}
unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
MachineBasicBlock::iterator I) {
assert(ScavengingFrameIndex >= 0 &&
"Cannot scavenge a register without an emergency spill slot!");
// Mask off the registers which are not in the TargetRegisterClass.
BitVector Candidates(NumPhysRegs, false);
CreateRegClassMask(RC, Candidates);
Candidates ^= ReservedRegs; // Do not include reserved registers.
// Exclude all the registers being used by the instruction.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
MachineOperand &MO = I->getOperand(i);
if (MO.isReg())
Candidates.reset(MO.getReg());
}
// Find the register whose use is furtherest aaway.
unsigned SReg = 0;
unsigned MaxDist = 0;
int Reg = Candidates.find_first();
while (Reg != -1) {
unsigned Dist = calcDistanceToUse(MBB, I, Reg);
if (Dist >= MaxDist) {
MaxDist = Dist;
SReg = Reg;
}
Reg = Candidates.find_next(Reg);
}
if (ScavengedReg != 0) {
// First restore previously scavenged register.
RegInfo->loadRegFromStackSlot(*MBB, I, ScavengedReg,
ScavengingFrameIndex, ScavengedRC);
MachineBasicBlock::iterator II = prior(I);
RegInfo->eliminateFrameIndex(II, this);
}
RegInfo->storeRegToStackSlot(*MBB, I, SReg, ScavengingFrameIndex, RC);
MachineBasicBlock::iterator II = prior(I);
RegInfo->eliminateFrameIndex(II, this);
ScavengedReg = SReg;
ScavengedRC = RC;
return SReg;
}