[VectorCombine] Add "VECTORCOMBINE on <FUNCTION_NAME>" title debug message to help finding vectorcombine stages in the debug log

Author: RKSimon

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

@@ -3032,6 +3032,8 @@ bool VectorCombine::run() {
   if (!TTI.getNumberOfRegisters(TTI.getRegisterClassForType(/*Vector*/ true)))
     return false;
 
+  LLVM_DEBUG(dbgs() << "\n\nVECTORCOMBINE on " << F.getName() << "\n");
+
   bool MadeChange = false;
   auto FoldInst = [this, &MadeChange](Instruction &I) {
     Builder.SetInsertPoint(&I);