[NFC] Make ConstantVector/ConstantDataVector::getType() return a FixedVectorType

[efriedma]

LGTM

llvm/include/llvm/IR/Constants.h

public:
   // ConstantVector accessors
   static Constant *get(ArrayRef<Constant*> V);
 
 private:
   static Constant *getImpl(ArrayRef<Constant *> V);
 
 public:
   /// Return a ConstantVector with the specified constant in each element.
+  /// Note that this might not return an instance of ConstantVector
   static Constant *getSplat(ElementCount EC, Constant *Elt);
 
-  /// Specialize the getType() method to always return a VectorType,
+  /// Specialize the getType() method to always return a FixedVectorType,
   /// which reduces the amount of casting needed in parts of the compiler.
-  inline VectorType *getType() const {
-    return cast<VectorType>(Value::getType());
+  inline FixedVectorType *getType() const {
+    return cast<FixedVectorType>(Value::getType());
   }
 
   /// If all elements of the vector constant have the same value, return that
   /// value. Otherwise, return nullptr. Ignore undefined elements by setting
   /// AllowUndefs to true.
   Constant *getSplatValue(bool AllowUndefs = false) const;
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
public:
   /// Returns true if this is a splat constant, meaning that all elements have
   /// the same value.
   bool isSplat() const;
 
   /// If this is a splat constant, meaning that all of the elements have the
   /// same value, return that value. Otherwise return NULL.
   Constant *getSplatValue() const;
 
-  /// Specialize the getType() method to always return a VectorType,
+  /// Specialize the getType() method to always return a FixedVectorType,
   /// which reduces the amount of casting needed in parts of the compiler.
-  inline VectorType *getType() const {
-    return cast<VectorType>(Value::getType());
+  inline FixedVectorType *getType() const {
+    return cast<FixedVectorType>(Value::getType());
   }
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const Value *V) {
     return V->getValueID() == ConstantDataVectorVal;
   }
 };