[SVE] Add specialized overloads of VectorType::get

[ctetreau]

Summary

Add overloads of get to FixedVectorType and ScalableVectorType that
mirror VectorType::get(Type *Ty, VectorType *VTy) that take and return
derived vector types

[ctetreau]

rebase

llvm/include/llvm/IR/DerivedTypes.h

 class FixedVectorType : public VectorType {
 protected:
   FixedVectorType(Type *ElTy, unsigned NumElts)
       : VectorType(ElTy, NumElts, FixedVectorTyID) {}
 
 public:
   static FixedVectorType *get(Type *ElementType, unsigned NumElts);
 
+  static FixedVectorType *get(Type *ElementType, const FixedVectorType *FVTy) {
+    return get(ElementType, FVTy->getNumElements());
+  }
+
   static bool classof(const Type *T) {
     return T->getTypeID() == FixedVectorTyID;
   }
 };
 
 /// Class to represent scalable SIMD vectors
 class ScalableVectorType : public VectorType {
 protected:
   ScalableVectorType(Type *ElTy, unsigned MinNumElts)
       : VectorType(ElTy, MinNumElts, ScalableVectorTyID) {}
 
 public:
   static ScalableVectorType *get(Type *ElementType, unsigned MinNumElts);
 
+  static ScalableVectorType *get(Type *ElementType,
+                                 const ScalableVectorType *SVTy) {
+    return get(ElementType, SVTy->getMinNumElements());
+  }
+
   /// Get the minimum number of elements in this vector. The actual number of
   /// elements in the vector is an integer multiple of this value.
   uint64_t getMinNumElements() const { return ElementQuantity; }
 
   static bool classof(const Type *T) {
     return T->getTypeID() == ScalableVectorTyID;
   }
 };