Do not insert one entry PHI nodes in split exit blocks!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10348 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/LoopSimplify.cpp

@@ -162,6 +162,15 @@ BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
   // incoming edges in BB into new PHI nodes in NewBB.
   //
   if (!Preds.empty()) {  // Is the loop not obviously dead?
+    if (Preds.size() == 1) {
+      // No need to insert one operand PHI nodes!  Instead, just update the
+      // incoming block ID's.
+      for (BasicBlock::iterator I = BB->begin();
+           PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+        unsigned i = PN->getBasicBlockIndex(Preds[0]);
+        PN->setIncomingBlock(i, NewBB);
+      }
+    } else {
       for (BasicBlock::iterator I = BB->begin();
            PHINode *PN = dyn_cast<PHINode>(I); ++I) {
         
@@ -175,9 +184,10 @@ BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
         }
         
         // Add an incoming value to the PHI node in the loop for the preheader
-      // edge
+        // edge.
         PN->addIncoming(NewPHI, NewBB);
       }
+    }
     
     // Now that the PHI nodes are updated, actually move the edges from
     // Preds to point to NewBB instead of BB.