[SLP] Add banner argument to SLP costs debug printer method - NFC.

[vdmitrie]

Summary

Removed unnecessary warning workaround.

[ABataev]

LG

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

LLVM_DUMP_METHOD void dump() const {
         dbgs() << EInfo << ", ";
       dbgs() << "\n";
     }
 #endif
   };
 
 #ifndef NDEBUG
   void dumpTreeCosts(const TreeEntry *E, InstructionCost ReuseShuffleCost,
-                     InstructionCost VecCost,
-                     InstructionCost ScalarCost) const {
-    dbgs() << "SLP: Calculated costs for Tree:\n"; E->dump();
+                     InstructionCost VecCost, InstructionCost ScalarCost,
+                     StringRef Banner) const {
+    dbgs() << "SLP: " << Banner << ":\n";
+    E->dump();
     dbgs() << "SLP: Costs:\n";
     dbgs() << "SLP:     ReuseShuffleCost = " << ReuseShuffleCost << "\n";
     dbgs() << "SLP:     VectorCost = " << VecCost << "\n";
     dbgs() << "SLP:     ScalarCost = " << ScalarCost << "\n";
-    dbgs() << "SLP:     ReuseShuffleCost + VecCost - ScalarCost = " <<
-               ReuseShuffleCost + VecCost - ScalarCost << "\n";
+    dbgs() << "SLP:     ReuseShuffleCost + VecCost - ScalarCost = "
+           << ReuseShuffleCost + VecCost - ScalarCost << "\n";
   }
 #endif
 
   /// Create a new VectorizableTree entry.
   TreeEntry *newTreeEntry(ArrayRef<Value *> VL,
                           std::optional<ScheduleData *> Bundle,
                           const InstructionsState &S,
                           const EdgeInfo &UserTreeIdx,
auto GetCostDiff =
           // instruction x total number of scalar instructions.
           ScalarCost = Sz * ScalarEltCost(0);
         } else {
           for (unsigned I = 0; I < Sz; ++I)
             ScalarCost += ScalarEltCost(I);
         }
 
         InstructionCost VecCost = VectorCost(CommonCost);
-        LLVM_DEBUG(
-            dumpTreeCosts(E, CommonCost, VecCost - CommonCost, ScalarCost));
-        // Disable warnings for `this` and `E` are unused. Required for
-        // `dumpTreeCosts`.
-        (void)this;
-        (void)E;
+        LLVM_DEBUG(dumpTreeCosts(E, CommonCost, VecCost - CommonCost,
+                                 ScalarCost, "Calculated costs for Tree"));
         return VecCost - ScalarCost;
       };
   // Calculate cost difference from vectorizing set of GEPs.
   // Negative value means vectorizing is profitable.
   auto GetGEPCostDiff = [=](ArrayRef<Value *> Ptrs, Value *BasePtr) {
     InstructionCost CostSavings = 0;
     for (Value *V : Ptrs) {
       if (V == BasePtr)