llvm-6502/lib/CodeGen/RegisterScavenging.cpp
2008-04-10 23:47:53 +00:00

413 lines
13 KiB
C++

//===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
//
// 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 register scavenger. It can provide
// information, such as unused registers, at any point in a machine basic block.
// It also provides a mechanism to make registers available 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/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
/// RedefinesSuperRegPart - Return true if the specified register is redefining
/// part of a super-register.
static bool RedefinesSuperRegPart(const MachineInstr *MI, unsigned SubReg,
const TargetRegisterInfo *TRI) {
bool SeenSuperUse = false;
bool SeenSuperDef = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister())
continue;
if (TRI->isSuperRegister(SubReg, MO.getReg()))
if (MO.isUse())
SeenSuperUse = true;
else if (MO.isImplicit())
SeenSuperDef = true;
}
return SeenSuperDef && SeenSuperUse;
}
static bool RedefinesSuperRegPart(const MachineInstr *MI,
const MachineOperand &MO,
const TargetRegisterInfo *TRI) {
assert(MO.isRegister() && MO.isDef() && "Not a register def!");
return RedefinesSuperRegPart(MI, MO.getReg(), TRI);
}
/// setUsed - Set the register and its sub-registers as being used.
void RegScavenger::setUsed(unsigned Reg, bool ImpDef) {
RegsAvailable.reset(Reg);
ImplicitDefed[Reg] = ImpDef;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs) {
RegsAvailable.reset(SubReg);
ImplicitDefed[SubReg] = ImpDef;
}
}
/// setUnused - Set the register and its sub-registers as being unused.
void RegScavenger::setUnused(unsigned Reg, const MachineInstr *MI) {
RegsAvailable.set(Reg);
ImplicitDefed.reset(Reg);
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs)
if (!RedefinesSuperRegPart(MI, Reg, TRI)) {
RegsAvailable.set(SubReg);
ImplicitDefed.reset(SubReg);
}
}
void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) {
const MachineFunction &MF = *mbb->getParent();
const TargetMachine &TM = MF.getTarget();
TII = TM.getInstrInfo();
TRI = TM.getRegisterInfo();
MRI = &MF.getRegInfo();
assert((NumPhysRegs == 0 || NumPhysRegs == TRI->getNumRegs()) &&
"Target changed?");
if (!MBB) {
NumPhysRegs = TRI->getNumRegs();
RegsAvailable.resize(NumPhysRegs);
ImplicitDefed.resize(NumPhysRegs);
// Create reserved registers bitvector.
ReservedRegs = TRI->getReservedRegs(MF);
// Create callee-saved registers bitvector.
CalleeSavedRegs.resize(NumPhysRegs);
const unsigned *CSRegs = TRI->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;
TII->loadRegFromStackSlot(*MBB, MBBI, ScavengedReg,
ScavengingFrameIndex, ScavengedRC);
MachineBasicBlock::iterator II = prior(MBBI);
TRI->eliminateFrameIndex(II, 0, this);
setUsed(ScavengedReg);
ScavengedReg = 0;
ScavengedRC = NULL;
}
/// isLiveInButUnusedBefore - Return true if register is livein the MBB not
/// not used before it reaches the MI that defines register.
static bool isLiveInButUnusedBefore(unsigned Reg, MachineInstr *MI,
MachineBasicBlock *MBB,
const TargetRegisterInfo *TRI,
MachineRegisterInfo* MRI) {
// First check if register is livein.
bool isLiveIn = false;
for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(),
E = MBB->livein_end(); I != E; ++I)
if (Reg == *I || TRI->isSuperRegister(Reg, *I)) {
isLiveIn = true;
break;
}
if (!isLiveIn)
return false;
// Is there any use of it before the specified MI?
SmallPtrSet<MachineInstr*, 4> UsesInMBB;
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
if (UseMI->getParent() == MBB)
UsesInMBB.insert(UseMI);
}
if (UsesInMBB.empty())
return true;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MI; I != E; ++I)
if (UsesInMBB.count(&*I))
return false;
return true;
}
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;
const TargetInstrDesc &TID = MI->getDesc();
// Reaching a terminator instruction. Restore a scavenged register (which
// must be life out.
if (TID.isTerminator())
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.isRegister() || !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 && "Using an undefined register!");
else
restoreScavengedReg();
}
if (MO.isKill() && !isReserved(Reg)) {
ChangedRegs.set(Reg);
// Mark sub-registers as changed if they aren't defined in the same
// instruction.
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs)
ChangedRegs.set(SubReg);
}
}
// Change states of all registers after all the uses are processed to guard
// against multiple uses.
setUnused(ChangedRegs);
// Process defs.
bool IsImpDef = MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
// If it's dead upon def, then it is now free.
if (MO.isDead()) {
setUnused(Reg, MI);
continue;
}
// Skip two-address destination operand.
if (TID.findTiedToSrcOperand(i) != -1) {
assert(isUsed(Reg) && "Using an undefined register!");
continue;
}
// Skip is this is merely redefining part of a super-register.
if (RedefinesSuperRegPart(MI, MO, TRI))
continue;
// Implicit def is allowed to "re-define" any register. Similarly,
// implicitly defined registers can be clobbered.
assert((isReserved(Reg) || isUnused(Reg) ||
IsImpDef || isImplicitlyDefined(Reg) ||
isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) &&
"Re-defining a live register!");
setUsed(Reg, IsImpDef);
}
}
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 TargetInstrDesc &TID = MI->getDesc();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister() || !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, MI);
}
// Process uses.
BitVector ChangedRegs(NumPhysRegs);
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister() || !MO.isUse())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
assert(isUnused(Reg) || isReserved(Reg));
ChangedRegs.set(Reg);
// Set the sub-registers as "used".
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs)
ChangedRegs.set(SubReg);
}
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,
const TargetRegisterInfo *TRI) {
unsigned Dist = 0;
I = next(I);
while (I != MBB->end()) {
Dist++;
if (I->readsRegister(Reg, TRI))
return Dist;
I = next(I);
}
return Dist + 1;
}
unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
MachineBasicBlock::iterator I,
int SPAdj) {
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.isRegister())
Candidates.reset(MO.getReg());
}
// Find the register whose use is furthest away.
unsigned SReg = 0;
unsigned MaxDist = 0;
int Reg = Candidates.find_first();
while (Reg != -1) {
unsigned Dist = calcDistanceToUse(MBB, I, Reg, TRI);
if (Dist >= MaxDist) {
MaxDist = Dist;
SReg = Reg;
}
Reg = Candidates.find_next(Reg);
}
if (ScavengedReg != 0) {
// First restore previously scavenged register.
TII->loadRegFromStackSlot(*MBB, I, ScavengedReg,
ScavengingFrameIndex, ScavengedRC);
MachineBasicBlock::iterator II = prior(I);
TRI->eliminateFrameIndex(II, SPAdj, this);
}
TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC);
MachineBasicBlock::iterator II = prior(I);
TRI->eliminateFrameIndex(II, SPAdj, this);
ScavengedReg = SReg;
ScavengedRC = RC;
return SReg;
}