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Complete support for two-address pass rematerialization. Now *almost* always a win.

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llvm-svn: 52452
This commit is contained in:
Evan Cheng 2008-06-18 07:49:14 +00:00
parent e447be0532
commit ad0a4a31f8
1 changed files with 128 additions and 49 deletions
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177
lib/CodeGen/TwoAddressInstructionPass.cpp
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@ -40,6 +40,8 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
@ -49,9 +51,10 @@ STATISTIC(NumTwoAddressInstrs, "Number of two-address instructions");
STATISTIC(NumCommuted , "Number of instructions commuted to coalesce");
STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address");
STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk");
STATISTIC(NumReMats, "Number of instructions re-materialized");
static cl::opt<bool>
EnableReMat("2-addr-remat", cl::init(false), cl::Hidden,
EnableReMat("two-addr-remat", cl::init(false), cl::Hidden,
cl::desc("Two-addr conversion should remat when possible."));
namespace {
@ -65,6 +68,12 @@ namespace {
bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned Reg,
MachineBasicBlock::iterator OldPos);
bool isSafeToReMat(unsigned DstReg, MachineInstr *MI);
bool isProfitableToReMat(unsigned Reg, const TargetRegisterClass *RC,
MachineInstr *MI, unsigned Loc,
MachineInstr *DefMI, MachineBasicBlock *MBB,
DenseMap<MachineInstr*, unsigned> &DistanceMap);
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass((intptr_t)&ID) {}
@ -93,7 +102,6 @@ const PassInfo *const llvm::TwoAddressInstructionPassID = &X;
/// three-address instruction to avoid clobbering a register. Try to sink it
/// past the instruction that would kill the above mentioned register to reduce
/// register pressure.
///
bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
MachineInstr *MI, unsigned SavedReg,
MachineBasicBlock::iterator OldPos) {
@ -127,7 +135,6 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
// Find the instruction that kills SavedReg.
MachineInstr *KillMI = NULL;
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(SavedReg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
@ -144,15 +151,18 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
// position and the kill use, then it's not safe to sink it.
//
// FIXME: This can be sped up if there is an easy way to query whether an
// instruction if before or after another instruction. Then we can use
// instruction is before or after another instruction. Then we can use
// MachineRegisterInfo def / use instead.
MachineOperand *KillMO = NULL;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
unsigned NumVisited = 0;
for (MachineBasicBlock::iterator I = next(OldPos); I != KillPos; ++I) {
MachineInstr *OtherMI = I;
if (NumVisited > 30) // FIXME: Arbitrary limit to reduce compile time cost.
return false;
++NumVisited;
for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = OtherMI->getOperand(i);
if (!MO.isRegister())
@ -165,8 +175,8 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
if (MO.isKill()) {
if (OtherMI == KillMI && MOReg == SavedReg)
// Save the operand that kills the register. We want unset the kill
// marker is we can sink MI past it.
// Save the operand that kills the register. We want to unset the kill
// marker if we can sink MI past it.
KillMO = &MO;
else if (UseRegs.count(MOReg))
// One of the uses is killed before the destination.
@ -191,6 +201,80 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
return true;
}
/// isSafeToReMat - Return true if it's safe to rematerialize the specified
/// instruction which defined the specified register instead of copying it.
bool
TwoAddressInstructionPass::isSafeToReMat(unsigned DstReg, MachineInstr *MI) {
const TargetInstrDesc &TID = MI->getDesc();
if (!TID.isAsCheapAsAMove())
return false;
bool SawStore = false;
if (!MI->isSafeToMove(TII, SawStore))
return false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister())
continue;
// FIXME: For now, do not remat any instruction with register operands.
// Later on, we can loosen the restriction is the register operands have
// not been modified between the def and use. Note, this is different from
// MachineSink because the code in no longer in two-address form (at least
// partially).
if (MO.isUse())
return false;
else if (!MO.isDead() && MO.getReg() != DstReg)
return false;
}
return true;
}
/// isTwoAddrUse - Return true if the specified MI is using the specified
/// register as a two-address operand.
static bool isTwoAddrUse(MachineInstr *UseMI, unsigned Reg) {
const TargetInstrDesc &TID = UseMI->getDesc();
for (unsigned i = 0, e = TID.getNumOperands(); i != e; ++i) {
MachineOperand &MO = UseMI->getOperand(i);
if (MO.getReg() == Reg &&
(MO.isDef() || TID.getOperandConstraint(i, TOI::TIED_TO) != -1))
// Earlier use is a two-address one.
return true;
}
return false;
}
/// isProfitableToReMat - Return true if the heuristics determines it is likely
/// to be profitable to re-materialize the definition of Reg rather than copy
/// the register.
bool
TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg,
const TargetRegisterClass *RC,
MachineInstr *MI, unsigned Loc,
MachineInstr *DefMI, MachineBasicBlock *MBB,
DenseMap<MachineInstr*, unsigned> &DistanceMap) {
if (DefMI->getParent() != MBB)
return true;
// If earlier uses in MBB are not two-address uses, then don't remat.
bool OtherUse = false;
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
if (!UseMO.isUse())
continue;
MachineInstr *UseMI = UseMO.getParent();
if (UseMI->getParent() != MBB)
continue;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);
if (DI != DistanceMap.end() && DI->second == Loc)
continue; // Current use.
OtherUse = true;
// There is at least one other use in the MBB that will clobber the
// register.
if (isTwoAddrUse(UseMI, Reg))
return true;
}
return !OtherUse;
}
/// runOnMachineFunction - Reduce two-address instructions to two operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
@ -206,16 +290,25 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
DOUT << "********** REWRITING TWO-ADDR INSTRS **********\n";
DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
SmallPtrSet<MachineInstr*, 8> ReMattedInstrs;
// ReMatRegs - Keep track of the registers whose def's are remat'ed.
BitVector ReMatRegs;
ReMatRegs.resize(MRI->getLastVirtReg()+1);
// DistanceMap - Keep track the distance of a MI from the start of the
// current basic block.
DenseMap<MachineInstr*, unsigned> DistanceMap;
for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
mbbi != mbbe; ++mbbi) {
unsigned Dist = 0;
DistanceMap.clear();
for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
mi != me; ) {
MachineBasicBlock::iterator nmi = next(mi);
const TargetInstrDesc &TID = mi->getDesc();
bool FirstTied = true;
DistanceMap.insert(std::make_pair(mi, ++Dist));
for (unsigned si = 1, e = TID.getNumOperands(); si < e; ++si) {
int ti = TID.getOperandConstraint(si, TOI::TIED_TO);
if (ti == -1)
@ -284,6 +377,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
mbbi->insert(mi, NewMI); // Insert the new inst
mbbi->erase(mi); // Nuke the old inst.
mi = NewMI;
DistanceMap.insert(std::make_pair(NewMI, Dist));
}
++NumCommuted;
@ -303,21 +397,23 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
assert(TID.getOperandConstraint(i, TOI::TIED_TO) == -1);
#endif
if (MachineInstr *New=TII->convertToThreeAddress(mbbi, mi, *LV)) {
MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, *LV);
if (NewMI) {
DOUT << "2addr: CONVERTING 2-ADDR: " << *mi;
DOUT << "2addr: TO 3-ADDR: " << *New;
DOUT << "2addr: TO 3-ADDR: " << *NewMI;
bool Sunk = false;
if (New->findRegisterUseOperand(regB, false, TRI))
if (NewMI->findRegisterUseOperand(regB, false, TRI))
// FIXME: Temporary workaround. If the new instruction doesn't
// uses regB, convertToThreeAddress must have created more
// then one instruction.
Sunk = Sink3AddrInstruction(mbbi, New, regB, mi);
Sunk = Sink3AddrInstruction(mbbi, NewMI, regB, mi);
mbbi->erase(mi); // Nuke the old inst.
if (!Sunk) {
mi = New;
DistanceMap.insert(std::make_pair(NewMI, Dist));
mi = NewMI;
nmi = next(mi);
}
@ -328,17 +424,17 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
}
InstructionRearranged:
const TargetRegisterClass* rc = MF.getRegInfo().getRegClass(regA);
MachineInstr *Orig = MRI->getVRegDef(regB);
const TargetInstrDesc &OrigTID = Orig->getDesc();
bool SawStore = false;
if (EnableReMat && Orig && Orig->isSafeToMove(TII, SawStore) &&
OrigTID.isAsCheapAsAMove() && !OrigTID.mayLoad() &&
!OrigTID.isSimpleLoad()) {
DEBUG(cerr << "2addr: REMATTING : " << *Orig << "\n");
TII->reMaterialize(*mbbi, mi, regA, Orig);
ReMattedInstrs.insert(Orig);
const TargetRegisterClass* rc = MRI->getRegClass(regA);
MachineInstr *DefMI = MRI->getVRegDef(regB);
// If it's safe and profitable, remat the definition instead of
// copying it.
if (EnableReMat && DefMI &&
isSafeToReMat(regB, DefMI) &&
isProfitableToReMat(regB, rc, mi, Dist, DefMI, mbbi,DistanceMap)){
DEBUG(cerr << "2addr: REMATTING : " << *DefMI << "\n");
TII->reMaterialize(*mbbi, mi, regA, DefMI);
ReMatRegs.set(regB);
++NumReMats;
} else {
TII->copyRegToReg(*mbbi, mi, regA, regB, rc, rc);
}
@ -378,33 +474,16 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
}
if (EnableReMat) {
// Check to see if the instructions that we rematerialized are now dead. If
// they are, expunge them here.
SmallPtrSet<MachineInstr*, 8>::iterator I = ReMattedInstrs.begin();
SmallPtrSet<MachineInstr*, 8>::iterator E = ReMattedInstrs.end();
for (; I != E; ++I) {
MachineInstr *MI = *I;
bool InstrDead = true;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isRegister())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg || !MO.isDef() || (MO.isImplicit() && MO.isDead()))
continue;
if (MRI->use_begin(MOReg) != MRI->use_end()) {
InstrDead = false;
break;
}
// Some remat'ed instructions are dead.
int VReg = ReMatRegs.find_first();
while (VReg != -1) {
if (MRI->use_empty(VReg)) {
MachineInstr *DefMI = MRI->getVRegDef(VReg);
DefMI->eraseFromParent();
}
if (InstrDead)
MI->eraseFromParent();
VReg = ReMatRegs.find_next(VReg);
}
}
return MadeChange;