- // Okay, the value isn't in the map and we just inserted a null in the entry
- // to indicate that we're processing the block. Since we have no idea what
- // value is in this block, we have to recurse through our predecessors.
- //
- // While we're walking our predecessors, we keep track of them in a vector,
- // then insert a PHI node in the end if we actually need one. We could use a
- // smallvector here, but that would take a lot of stack space for every level
- // of the recursion, just use IncomingPredInfo as an explicit stack.
- IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
- unsigned FirstPredInfoEntry = IncomingPredInfo.size();
-
- // As we're walking the predecessors, keep track of whether they are all
- // producing the same value. If so, this value will capture it, if not, it
- // will get reset to null. We distinguish the no-predecessor case explicitly
- // below.
- unsigned SingularValue = 0;
- bool isFirstPred = true;
- for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
- E = BB->pred_end(); PI != E; ++PI) {
- MachineBasicBlock *PredBB = *PI;
- unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
- IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
-
- // Compute SingularValue.
- if (isFirstPred) {
- SingularValue = PredVal;
- isFirstPred = false;
- } else if (PredVal != SingularValue)
- SingularValue = 0;
+ /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
+ /// Add it into the specified block and return the register.
+ static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
+ MachineSSAUpdater *Updater) {
+ MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
+ MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
+ Updater->VRC, Updater->MRI,
+ Updater->TII);
+ return PHI->getOperand(0).getReg();