Factor some code into a new FoldSingleEntryPHINodes method.

llvm-svn: 60501

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -54,6 +54,24 @@ void llvm::DeleteDeadBlock(BasicBlock *BB) {
   BB->eraseFromParent();
 }
 
+/// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
+/// any single-entry PHI nodes in it, fold them away.  This handles the case
+/// when all entries to the PHI nodes in a block are guaranteed equal, such as
+/// when the block has exactly one predecessor.
+void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
+  if (!isa<PHINode>(BB->begin()))
+    return;
+  
+  while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+    if (PN->getIncomingValue(0) != PN)
+      PN->replaceAllUsesWith(PN->getIncomingValue(0));
+    else
+      PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+    PN->eraseFromParent();
+  }
+}
+
+
 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
 /// if possible.  The return value indicates success or failure.
 bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {