add debug message

Author: ParkHanbum

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

@@ -723,6 +723,9 @@ bool VectorCombine::foldInsExtFNeg(Instruction &I) {
                                   SrcVecTy, SrcMask, CostKind);
   }
 
+  LLVM_DEBUG(dbgs() << "Found an insertion of (extract)fneg : " << I
+                    << "\n  OldCost: " << OldCost << " vs NewCost: " << NewCost
+                    << "\n");
   if (NewCost > OldCost)
     return false;