// to be sunk then it's probably worth it.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg()) continue;
+ if (!MO.isReg() || !MO.isUse())
+ continue;
unsigned Reg = MO.getReg();
- if (Reg == 0 || !TargetRegisterInfo::isPhysicalRegister(Reg))
+ if (Reg == 0)
continue;
- if (MRI->hasOneNonDBGUse(Reg))
- return true;
+
+ // We don't move live definitions of physical registers,
+ // so sinking their uses won't enable any opportunities.
+ if (TargetRegisterInfo::isPhysicalRegister(Reg))
+ continue;
+
+ // If this instruction is the only user of a virtual register,
+ // check if breaking the edge will enable sinking
+ // both this instruction and the defining instruction.
+ if (MRI->hasOneNonDBGUse(Reg)) {
+ // If the definition resides in same MBB,
+ // claim it's likely we can sink these together.
+ // If definition resides elsewhere, we aren't
+ // blocking it from being sunk so don't break the edge.
+ MachineInstr *DefMI = MRI->getVRegDef(Reg);
+ if (DefMI->getParent() == MI->getParent())
+ return true;
+ }
}
return false;
/// collectDebgValues - Scan instructions following MI and collect any
/// matching DBG_VALUEs.
static void collectDebugValues(MachineInstr *MI,
- SmallVector<MachineInstr *, 2> & DbgValues) {
+ SmallVectorImpl<MachineInstr *> &DbgValues) {
DbgValues.clear();
if (!MI->getOperand(0).isReg())
return;
DEBUG(dbgs() << "Sink instr " << *MI << "\tinto block " << *SuccToSinkTo);
- // If the block has multiple predecessors, this would introduce computation on
- // a path that it doesn't already exist. We could split the critical edge,
- // but for now we just punt.
+ // If the block has multiple predecessors, this is a critical edge.
+ // Decide if we can sink along it or need to break the edge.
if (SuccToSinkTo->pred_size() > 1) {
// We cannot sink a load across a critical edge - there may be stores in
// other code paths.