+ if (PI == PE)
+ return Unknown;
+
+ // If V is a PHI node in the same block as the context, we need to ask
+ // questions about the predicate as applied to the incoming value along
+ // each edge. This is useful for eliminating cases where the predicate is
+ // known along all incoming edges.
+ if (auto *PHI = dyn_cast<PHINode>(V))
+ if (PHI->getParent() == BB) {
+ Tristate Baseline = Unknown;
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i < e; i++) {
+ Value *Incoming = PHI->getIncomingValue(i);
+ BasicBlock *PredBB = PHI->getIncomingBlock(i);
+ // Note that PredBB may be BB itself.
+ Tristate Result = getPredicateOnEdge(Pred, Incoming, C, PredBB, BB,
+ CxtI);
+
+ // Keep going as long as we've seen a consistent known result for
+ // all inputs.
+ Baseline = (i == 0) ? Result /* First iteration */
+ : (Baseline == Result ? Baseline : Unknown); /* All others */
+ if (Baseline == Unknown)
+ break;
+ }
+ if (Baseline != Unknown)
+ return Baseline;
+ }
+
+ // For a comparison where the V is outside this block, it's possible
+ // that we've branched on it before. Look to see if the value is known
+ // on all incoming edges.
+ if (!isa<Instruction>(V) ||
+ cast<Instruction>(V)->getParent() != BB) {