DeadMemOpElimination::instr_iterator
DeadMemOpElimination::handleMemOp(instr_iterator I, DefMapTy &Defs,
AliasSetTracker &AST) {
MachineInstr *MI = I;
MachineMemOperand *MO = *MI->memoperands_begin();
// AliasAnalysis cannot handle offset right now, so we pretend to write a
// a big enough size to the location pointed by the base pointer.
uint64_t Size = MO->getSize() + MO->getOffset();
AliasSet *ASet = &AST.getAliasSetForPointer(const_cast<Value*>(MO->getValue()),
Size, 0);
MachineInstr *&LastMI = Defs[ASet];
bool canHandleLastStore = LastMI && ASet->isMustAlias()
&& LastMI->getOpcode() != VTM::VOpInternalCall
// FIXME: We may need to remember the last
// definition for all predicates.
&& isPredIdentical(LastMI, MI);
if (canHandleLastStore) {
MachineMemOperand *LastMO = *LastMI->memoperands_begin();
// We can only handle last store if and only if their memory operand have
// the must-alias address and the same size.
canHandleLastStore = LastMO->getSize() == MO->getSize()
&& !LastMO->isVolatile()
&& MachineMemOperandAlias(MO, LastMO, AA, SE)
== AliasAnalysis::MustAlias;
}
// FIXME: These elimination is only valid if we are in single-thread mode!
if (VInstrInfo::mayStore(MI)) {
if (canHandleLastStore) {
// Dead store find, remove it.
LastMI->eraseFromParent();
++DeadStoreEliminated;
}
// Update the definition.
LastMI = MI;
return I;
}
// Now MI is a load.
if (!canHandleLastStore) return I;
// Loading the value that just be stored, the load is not necessary.
MachineOperand LoadedMO = MI->getOperand(0);
MachineOperand StoredMO = LastMI->getOperand(2);
// Simply replace the load by a copy.
DebugLoc dl = MI->getDebugLoc();
I = *BuildMI(*MI->getParent(), I, dl, VInstrInfo::getDesc(VTM::VOpMove))
.addOperand(LoadedMO).addOperand(StoredMO).
addOperand(*VInstrInfo::getPredOperand(MI)).
addOperand(*VInstrInfo::getTraceOperand(MI));
MI->eraseFromParent();
++DeadLoadEliminated;
return I;
}
