+ if (InstList.empty()) return;
+ PHINode *APN = dyn_cast<PHINode>(&front());
+ if (!APN) return; // Quick exit.
+
+ // If there are exactly two predecessors, then we want to nuke the PHI nodes
+ // altogether. However, we cannot do this, if this in this case:
+ //
+ // Loop:
+ // %x = phi [X, Loop]
+ // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
+ // br Loop ;; %x2 does not dominate all uses
+ //
+ // This is because the PHI node input is actually taken from the predecessor
+ // basic block. The only case this can happen is with a self loop, so we
+ // check for this case explicitly now.
+ //
+ unsigned max_idx = APN->getNumIncomingValues();
+ assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
+ if (max_idx == 2) {
+ BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
+
+ // Disable PHI elimination!
+ if (this == Other) max_idx = 3;
+ }
+
+ // <= Two predecessors BEFORE I remove one?
+ if (max_idx <= 2 && !DontDeleteUselessPHIs) {
+ // Yup, loop through and nuke the PHI nodes
+ while (PHINode *PN = dyn_cast<PHINode>(&front())) {
+ // Remove the predecessor first.
+ PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
+
+ // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
+ if (max_idx == 2) {
+ if (PN->getOperand(0) != PN)
+ PN->replaceAllUsesWith(PN->getOperand(0));
+ else
+ // We are left with an infinite loop with no entries: kill the PHI.
+ PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ getInstList().pop_front(); // Remove the PHI node
+ }
+
+ // If the PHI node already only had one entry, it got deleted by
+ // removeIncomingValue.
+ }
+ } else {
+ // Okay, now we know that we need to remove predecessor #pred_idx from all
+ // PHI nodes. Iterate over each PHI node fixing them up
+ PHINode *PN;
+ for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
+ ++II;
+ PN->removeIncomingValue(Pred, false);
+ // If all incoming values to the Phi are the same, we can replace the Phi
+ // with that value.
+ if (Value *PNV = PN->hasConstantValue()) {
+ PN->replaceAllUsesWith(PNV);
+ PN->eraseFromParent();
+ }
+ }
+ }