+
+/// SplitEdgeNicely - Split the critical edge from TI to it's specified
+/// successor if it will improve codegen. We only do this if the successor has
+/// phi nodes (otherwise critical edges are ok). If there is already another
+/// predecessor of the succ that is empty (and thus has no phi nodes), use it
+/// instead of introducing a new block.
+static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
+ BasicBlock *TIBB = TI->getParent();
+ BasicBlock *Dest = TI->getSuccessor(SuccNum);
+ assert(isa<PHINode>(Dest->begin()) &&
+ "This should only be called if Dest has a PHI!");
+
+ /// TIPHIValues - This array is lazily computed to determine the values of
+ /// PHIs in Dest that TI would provide.
+ std::vector<Value*> TIPHIValues;
+
+ // Check to see if Dest has any blocks that can be used as a split edge for
+ // this terminator.
+ for (pred_iterator PI = pred_begin(Dest), E = pred_end(Dest); PI != E; ++PI) {
+ BasicBlock *Pred = *PI;
+ // To be usable, the pred has to end with an uncond branch to the dest.
+ BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
+ if (!PredBr || !PredBr->isUnconditional() ||
+ // Must be empty other than the branch.
+ &Pred->front() != PredBr)
+ continue;
+
+ // Finally, since we know that Dest has phi nodes in it, we have to make
+ // sure that jumping to Pred will have the same affect as going to Dest in
+ // terms of PHI values.
+ PHINode *PN;
+ unsigned PHINo = 0;
+ bool FoundMatch = true;
+ for (BasicBlock::iterator I = Dest->begin();
+ (PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
+ if (PHINo == TIPHIValues.size())
+ TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB));
+
+ // If the PHI entry doesn't work, we can't use this pred.
+ if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) {
+ FoundMatch = false;
+ break;
+ }
+ }
+
+ // If we found a workable predecessor, change TI to branch to Succ.
+ if (FoundMatch) {
+ Dest->removePredecessor(TIBB);
+ TI->setSuccessor(SuccNum, Pred);
+ return;
+ }
+ }
+
+ SplitCriticalEdge(TI, SuccNum, P, true);
+}
+
+