bool
MachineCSE::isPhysDefTriviallyDead(unsigned Reg,
MachineBasicBlock::const_iterator I,
MachineBasicBlock::const_iterator E) const {
unsigned LookAheadLeft = LookAheadLimit;
while (LookAheadLeft) {
// Skip over dbg_value's.
while (I != E && I->isDebugValue())
++I;
if (I == E)
// Reached end of block, register is obviously dead.
return true;
bool SeenDef = false;
for (const MachineOperand &MO : I->operands()) {
if (MO.isRegMask() && MO.clobbersPhysReg(Reg))
SeenDef = true;
if (!MO.isReg() || !MO.getReg())
continue;
if (!TRI->regsOverlap(MO.getReg(), Reg))
continue;
if (MO.isUse())
// Found a use!
return false;
SeenDef = true;
}
if (SeenDef)
// See a def of Reg (or an alias) before encountering any use, it's
// trivially dead.
return true;
--LookAheadLeft;
++I;
}
return false;
}
bool MachineCSE::PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
SmallSet<unsigned,8> &PhysRefs,
SmallVectorImpl<unsigned> &PhysDefs,
bool &NonLocal) const {
// For now conservatively returns false if the common subexpression is
// not in the same basic block as the given instruction. The only exception
// is if the common subexpression is in the sole predecessor block.
const MachineBasicBlock *MBB = MI->getParent();
const MachineBasicBlock *CSMBB = CSMI->getParent();
bool CrossMBB = false;
if (CSMBB != MBB) {
if (MBB->pred_size() != 1 || *MBB->pred_begin() != CSMBB)
return false;
for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i) {
if (MRI->isAllocatable(PhysDefs[i]) || MRI->isReserved(PhysDefs[i]))
// Avoid extending live range of physical registers if they are
//allocatable or reserved.
return false;
}
CrossMBB = true;
}
MachineBasicBlock::const_iterator I = CSMI; I = std::next(I);
MachineBasicBlock::const_iterator E = MI;
MachineBasicBlock::const_iterator EE = CSMBB->end();
unsigned LookAheadLeft = LookAheadLimit;
while (LookAheadLeft) {
// Skip over dbg_value's.
while (I != E && I != EE && I->isDebugValue())
++I;
if (I == EE) {
assert(CrossMBB && "Reaching end-of-MBB without finding MI?");
(void)CrossMBB;
CrossMBB = false;
NonLocal = true;
I = MBB->begin();
EE = MBB->end();
continue;
}
if (I == E)
return true;
for (const MachineOperand &MO : I->operands()) {
// RegMasks go on instructions like calls that clobber lots of physregs.
// Don't attempt to CSE across such an instruction.
if (MO.isRegMask())
return false;
if (!MO.isReg() || !MO.isDef())
continue;
unsigned MOReg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(MOReg))
continue;
if (PhysRefs.count(MOReg))
return false;
}
--LookAheadLeft;
++I;
}
return false;
}
