[LV] Use MapVector for ScalarCostsTy for deterministic iter order (NFC)

We iterate over the scalar costs of instruction when printing costs, and
currently the iteration order is not deterministic. Currently no tests
check the output with multiple instructions in the map, but those will
come soon.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -1562,7 +1562,7 @@ class LoopVectorizationCostModel {
   /// A type representing the costs for instructions if they were to be
   /// scalarized rather than vectorized. The entries are Instruction-Cost
   /// pairs.
-  using ScalarCostsTy = DenseMap<Instruction *, InstructionCost>;
+  using ScalarCostsTy = MapVector<Instruction *, InstructionCost>;
 
   /// A set containing all BasicBlocks that are known to present after
   /// vectorization as a predicated block.
@@ -4925,7 +4925,8 @@ void LoopVectorizationCostModel::collectInstsToScalarize(ElementCount VF) {
         if (!isScalarAfterVectorization(&I, VF) && !VF.isScalable() &&
             !useEmulatedMaskMemRefHack(&I, VF) &&
             computePredInstDiscount(&I, ScalarCosts, VF) >= 0) {
-          ScalarCostsVF.insert_range(ScalarCosts);
+          for (const auto &[I, IC] : ScalarCosts)
+            ScalarCostsVF.insert({I, IC});
           // Check if we decided to scalarize a call. If so, update the widening
           // decision of the call to CM_Scalarize with the computed scalar cost.
           for (const auto &[I, Cost] : ScalarCosts) {