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TwoAddressInstructionPass enhancement. After it converts a two address instruction into a 3-address one, sink it past the instruction that kills the read-mod-write register if its definition is used past the kill. This reduces the number of live register by one.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48333 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2008-03-13 06:37:55 +00:00
parent 6634e26aa1
commit 875357d213
3 changed files with 161 additions and 14 deletions
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144
lib/CodeGen/TwoAddressInstructionPass.cpp
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@ -37,8 +37,9 @@
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
@ -46,10 +47,22 @@ using namespace llvm;
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");
namespace {
static cl::opt<int>
SinkLimit("two-addr-sink-limit", cl::init(-1), cl::Hidden);
}
namespace {
struct VISIBILITY_HIDDEN TwoAddressInstructionPass
: public MachineFunctionPass {
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
MachineRegisterInfo *MRI;
LiveVariables *LV;
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass((intptr_t)&ID) {}
@ -57,6 +70,11 @@ namespace {
/// runOnMachineFunction - pass entry point
bool runOnMachineFunction(MachineFunction&);
private:
bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned Reg,
MachineBasicBlock::iterator OldPos);
};
char TwoAddressInstructionPass::ID = 0;
@ -75,14 +93,113 @@ void TwoAddressInstructionPass::getAnalysisUsage(AnalysisUsage &AU) const {
MachineFunctionPass::getAnalysisUsage(AU);
}
/// Sink3AddrInstruction - A two-address instruction has been converted to a
/// 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) {
// Check if it's safe to move this instruction.
bool SeenStore = true; // Be conservative.
if (!MI->isSafeToMove(TII, SeenStore))
return false;
unsigned DefReg = 0;
SmallSet<unsigned, 4> UseRegs;
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)
continue;
if (MO.isUse() && MOReg != SavedReg)
UseRegs.insert(MO.getReg());
if (!MO.isDef())
continue;
if (MO.isImplicit())
// Don't try to move it if it implicitly defines a register.
return false;
if (DefReg)
// For now, don't move any instructions that define multiple registers.
return false;
DefReg = MO.getReg();
}
// 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();
if (!UseMO.isKill())
continue;
KillMI = UseMO.getParent();
break;
}
if (!KillMI || KillMI->getParent() != MBB)
return false;
// If any of the definitions are used by another instruction between
// the 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 MachineRegisterInfo def / use instead.
MachineOperand *KillMO = NULL;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
for (MachineBasicBlock::iterator I = next(OldPos); I != KillPos; ++I) {
MachineInstr *OtherMI = I;
for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = OtherMI->getOperand(i);
if (!MO.isRegister())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (DefReg == MOReg)
return false;
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.
KillMO = &MO;
else if (UseRegs.count(MOReg))
// One of the uses is killed before the destination.
return false;
}
}
}
if (SinkLimit != -1 && Num3AddrSunk == (unsigned)SinkLimit)
return false;
// Update kill and LV information.
KillMO->setIsKill(false);
KillMO = MI->findRegisterUseOperand(SavedReg, false, TRI);
KillMO->setIsKill(true);
LiveVariables::VarInfo& VarInfo = LV->getVarInfo(SavedReg);
VarInfo.removeKill(KillMI);
VarInfo.Kills.push_back(MI);
// Move instruction to its destination.
MBB->remove(MI);
MBB->insert(KillPos, MI);
++Num3AddrSunk;
return true;
}
/// runOnMachineFunction - Reduce two-address instructions to two
/// operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
DOUT << "Machine Function\n";
const TargetMachine &TM = MF.getTarget();
const TargetInstrInfo &TII = *TM.getInstrInfo();
LiveVariables &LV = getAnalysis<LiveVariables>();
MRI = &MF.getRegInfo();
TII = TM.getInstrInfo();
TRI = TM.getRegisterInfo();
LV = &getAnalysis<LiveVariables>();
bool MadeChange = false;
@ -150,14 +267,14 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
unsigned regC = mi->getOperand(3-si).getReg();
if (mi->killsRegister(regC)) {
DOUT << "2addr: COMMUTING : " << *mi;
MachineInstr *NewMI = TII.commuteInstruction(mi);
MachineInstr *NewMI = TII->commuteInstruction(mi);
if (NewMI == 0) {
DOUT << "2addr: COMMUTING FAILED!\n";
} else {
DOUT << "2addr: COMMUTED TO: " << *NewMI;
// If the instruction changed to commute it, update livevar.
if (NewMI != mi) {
LV.instructionChanged(mi, NewMI); // Update live variables
LV->instructionChanged(mi, NewMI); // Update live variables
mbbi->insert(mi, NewMI); // Insert the new inst
mbbi->erase(mi); // Nuke the old inst.
mi = NewMI;
@ -180,11 +297,12 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
assert(TID.getOperandConstraint(i, TOI::TIED_TO) == -1);
#endif
if (MachineInstr *New = TII.convertToThreeAddress(mbbi, mi, LV)) {
if (MachineInstr *New=TII->convertToThreeAddress(mbbi, mi, *LV)) {
DOUT << "2addr: CONVERTING 2-ADDR: " << *mi;
DOUT << "2addr: TO 3-ADDR: " << *New;
bool Sunk = Sink3AddrInstruction(mbbi, New, regB, mi);
mbbi->erase(mi); // Nuke the old inst.
mi = New;
if (!Sunk) mi = New;
++NumConvertedTo3Addr;
// Done with this instruction.
break;
@ -194,20 +312,20 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
InstructionRearranged:
const TargetRegisterClass* rc = MF.getRegInfo().getRegClass(regA);
TII.copyRegToReg(*mbbi, mi, regA, regB, rc, rc);
TII->copyRegToReg(*mbbi, mi, regA, regB, rc, rc);
MachineBasicBlock::iterator prevMi = prior(mi);
DOUT << "\t\tprepend:\t"; DEBUG(prevMi->print(*cerr.stream(), &TM));
// update live variables for regB
LiveVariables::VarInfo& varInfoB = LV.getVarInfo(regB);
LiveVariables::VarInfo& varInfoB = LV->getVarInfo(regB);
// regB is used in this BB.
varInfoB.UsedBlocks[mbbi->getNumber()] = true;
if (LV.removeVirtualRegisterKilled(regB, mbbi, mi))
LV.addVirtualRegisterKilled(regB, prevMi);
if (LV->removeVirtualRegisterKilled(regB, mbbi, mi))
LV->addVirtualRegisterKilled(regB, prevMi);
if (LV.removeVirtualRegisterDead(regB, mbbi, mi))
LV.addVirtualRegisterDead(regB, prevMi);
if (LV->removeVirtualRegisterDead(regB, mbbi, mi))
LV->addVirtualRegisterDead(regB, prevMi);
// replace all occurences of regB with regA
for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) {