[VPlan] Only generate exit blocks for unique exit blocks.

Make sure we don't generate unnecessary blocks.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -858,7 +858,7 @@ VPlan::VPlan(Loop *L) {
   ScalarHeader = createVPIRBasicBlock(L->getHeader());
 
   SmallVector<BasicBlock *> IRExitBlocks;
-  L->getExitBlocks(IRExitBlocks);
+  L->getUniqueExitBlocks(IRExitBlocks);
   for (BasicBlock *EB : IRExitBlocks)
     ExitBlocks.push_back(createVPIRBasicBlock(EB));
 }