/// optimizeExtInstr - If instruction is a copy-like instruction, i.e. it reads
/// a single register and writes a single register and it does not modify the
/// source, and if the source value is preserved as a sub-register of the
/// result, then replace all reachable uses of the source with the subreg of the
/// result.
///
/// Do not generate an EXTRACT that is used only in a debug use, as this changes
/// the code. Since this code does not currently share EXTRACTs, just ignore all
/// debug uses.
bool PeepholeOptimizer::
optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
unsigned SrcReg, DstReg, SubIdx;
if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx))
return false;
if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
TargetRegisterInfo::isPhysicalRegister(SrcReg))
return false;
if (MRI->hasOneNonDBGUse(SrcReg))
// No other uses.
return false;
// Ensure DstReg can get a register class that actually supports
// sub-registers. Don't change the class until we commit.
const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
DstRC = TM->getRegisterInfo()->getSubClassWithSubReg(DstRC, SubIdx);
if (!DstRC)
return false;
// The ext instr may be operating on a sub-register of SrcReg as well.
// PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit
// register.
// If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of
// SrcReg:SubIdx should be replaced.
bool UseSrcSubIdx = TM->getRegisterInfo()->
getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != 0;
// The source has other uses. See if we can replace the other uses with use of
// the result of the extension.
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(DstReg), UE = MRI->use_nodbg_end();
UI != UE; ++UI)
ReachedBBs.insert(UI->getParent());
// Uses that are in the same BB of uses of the result of the instruction.
SmallVector<MachineOperand*, 8> Uses;
// Uses that the result of the instruction can reach.
SmallVector<MachineOperand*, 8> ExtendedUses;
bool ExtendLife = true;
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(SrcReg), UE = MRI->use_nodbg_end();
UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
MachineInstr *UseMI = &*UI;
if (UseMI == MI)
continue;
if (UseMI->isPHI()) {
ExtendLife = false;
continue;
}
// Only accept uses of SrcReg:SubIdx.
if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx)
continue;
// It's an error to translate this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
//
// into this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1027 = COPY %reg1025:4
// %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
//
// The problem here is that SUBREG_TO_REG is there to assert that an
// implicit zext occurs. It doesn't insert a zext instruction. If we allow
// the COPY here, it will give us the value after the <sext>, not the
// original value of %reg1024 before <sext>.
if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
continue;
MachineBasicBlock *UseMBB = UseMI->getParent();
if (UseMBB == MBB) {
// Local uses that come after the extension.
if (!LocalMIs.count(UseMI))
Uses.push_back(&UseMO);
} else if (ReachedBBs.count(UseMBB)) {
// Non-local uses where the result of the extension is used. Always
// replace these unless it's a PHI.
Uses.push_back(&UseMO);
} else if (Aggressive && DT->dominates(MBB, UseMBB)) {
// We may want to extend the live range of the extension result in order
// to replace these uses.
ExtendedUses.push_back(&UseMO);
} else {
// Both will be live out of the def MBB anyway. Don't extend live range of
// the extension result.
ExtendLife = false;
break;
}
}
if (ExtendLife && !ExtendedUses.empty())
// Extend the liveness of the extension result.
std::copy(ExtendedUses.begin(), ExtendedUses.end(),
std::back_inserter(Uses));
// Now replace all uses.
bool Changed = false;
if (!Uses.empty()) {
SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
// Look for PHI uses of the extended result, we don't want to extend the
// liveness of a PHI input. It breaks all kinds of assumptions down
// stream. A PHI use is expected to be the kill of its source values.
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(DstReg), UE = MRI->use_nodbg_end();
UI != UE; ++UI)
if (UI->isPHI())
PHIBBs.insert(UI->getParent());
const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
MachineOperand *UseMO = Uses[i];
MachineInstr *UseMI = UseMO->getParent();
MachineBasicBlock *UseMBB = UseMI->getParent();
if (PHIBBs.count(UseMBB))
continue;
// About to add uses of DstReg, clear DstReg's kill flags.
if (!Changed) {
MRI->clearKillFlags(DstReg);
MRI->constrainRegClass(DstReg, DstRC);
}
unsigned NewVR = MRI->createVirtualRegister(RC);
MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
TII->get(TargetOpcode::COPY), NewVR)
.addReg(DstReg, 0, SubIdx);
// SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set.
if (UseSrcSubIdx) {
Copy->getOperand(0).setSubReg(SubIdx);
Copy->getOperand(0).setIsUndef();
}
UseMO->setReg(NewVR);
++NumReuse;
Changed = true;
}
}
return Changed;
}
/// OptimizeInstr - If instruction is a copy-like instruction, i.e. it reads
/// a single register and writes a single register and it does not modify
/// the source, and if the source value is preserved as a sub-register of
/// the result, then replace all reachable uses of the source with the subreg
/// of the result.
/// Do not generate an EXTRACT that is used only in a debug use, as this
/// changes the code. Since this code does not currently share EXTRACTs, just
/// ignore all debug uses.
bool OptimizeExts::OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
bool Changed = false;
LocalMIs.insert(MI);
unsigned SrcReg, DstReg, SubIdx;
if (TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) {
if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
TargetRegisterInfo::isPhysicalRegister(SrcReg))
return false;
MachineRegisterInfo::use_nodbg_iterator UI = MRI->use_nodbg_begin(SrcReg);
if (++UI == MRI->use_nodbg_end())
// No other uses.
return false;
// Ok, the source has other uses. See if we can replace the other uses
// with use of the result of the extension.
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
UI = MRI->use_nodbg_begin(DstReg);
for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
UI != UE; ++UI)
ReachedBBs.insert(UI->getParent());
bool ExtendLife = true;
// Uses that are in the same BB of uses of the result of the instruction.
SmallVector<MachineOperand*, 8> Uses;
// Uses that the result of the instruction can reach.
SmallVector<MachineOperand*, 8> ExtendedUses;
UI = MRI->use_nodbg_begin(SrcReg);
for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
MachineInstr *UseMI = &*UI;
if (UseMI == MI)
continue;
if (UseMI->isPHI()) {
ExtendLife = false;
continue;
}
// It's an error to translate this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
//
// into this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1027 = COPY %reg1025:4
// %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
//
// The problem here is that SUBREG_TO_REG is there to assert that an
// implicit zext occurs. It doesn't insert a zext instruction. If we allow
// the COPY here, it will give us the value after the <sext>,
// not the original value of %reg1024 before <sext>.
if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
continue;
MachineBasicBlock *UseMBB = UseMI->getParent();
if (UseMBB == MBB) {
// Local uses that come after the extension.
if (!LocalMIs.count(UseMI))
Uses.push_back(&UseMO);
} else if (ReachedBBs.count(UseMBB))
// Non-local uses where the result of extension is used. Always
// replace these unless it's a PHI.
Uses.push_back(&UseMO);
else if (Aggressive && DT->dominates(MBB, UseMBB))
// We may want to extend live range of the extension result in order
// to replace these uses.
ExtendedUses.push_back(&UseMO);
else {
// Both will be live out of the def MBB anyway. Don't extend live
// range of the extension result.
ExtendLife = false;
break;
}
}
if (ExtendLife && !ExtendedUses.empty())
// Ok, we'll extend the liveness of the extension result.
std::copy(ExtendedUses.begin(), ExtendedUses.end(),
std::back_inserter(Uses));
// Now replace all uses.
if (!Uses.empty()) {
SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
// Look for PHI uses of the extended result, we don't want to extend the
// liveness of a PHI input. It breaks all kinds of assumptions down
// stream. A PHI use is expected to be the kill of its source values.
UI = MRI->use_nodbg_begin(DstReg);
for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
UI != UE; ++UI)
if (UI->isPHI())
PHIBBs.insert(UI->getParent());
const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
MachineOperand *UseMO = Uses[i];
MachineInstr *UseMI = UseMO->getParent();
MachineBasicBlock *UseMBB = UseMI->getParent();
if (PHIBBs.count(UseMBB))
continue;
unsigned NewVR = MRI->createVirtualRegister(RC);
BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
TII->get(TargetOpcode::COPY), NewVR)
.addReg(DstReg, 0, SubIdx);
UseMO->setReg(NewVR);
++NumReuse;
Changed = true;
}
}
}
return Changed;
}