///
DenseMap<AllocaInst*, unsigned> AllocaLookup;
- /// NewPhiNodes - The PhiNodes we're adding.
+ /// NewPhiNodes - The PhiNodes we're adding. That map is used to simplify
+ /// some Phi nodes as we iterate over it, so it should have deterministic
+ /// iterators. We could use a MapVector, but since we already maintain a
+ /// map from BasicBlock* to a stable numbering (BBNumbers), the DenseMap is
+ /// more efficient (also supports removal).
///
DenseMap<std::pair<unsigned, unsigned>, PHINode*> NewPhiNodes;
while (EliminatedAPHI) {
EliminatedAPHI = false;
+ // Iterating over NewPhiNodes is deterministic, so it is safe to try to
+ // simplify and RUAW them as we go. If it was not, we could add uses to
+ // the values we replace with in a non deterministic order, thus creating
+ // non deterministic def->use chains.
for (DenseMap<std::pair<unsigned, unsigned>, PHINode*>::iterator I =
NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) {
PHINode *PN = I->second;