Value types is the set of non-array object types. These types are
assignable, can be used as function parameters, and as return types
(along with void), and in other scenarios where the type must have usual
value-like behaviour with no weirdness (such as array decay).
`mlir::Type` is now used as the default C++ type for representing all
MLIR types, even when `ValueType` would be a valid constraint, unless
doing so provides a clear benefit in that specific context.
* PrimitiveType is now an interface.
* VoidKind is now VoidType.
* FloatKind is now FloatType.
* The integer kinds are now IntegerType with IntegerKind.
* DecayOp - array or function to pointer decay. Not shown in C.
* BitCastOp - bit-preserving conversion. Emitted as bit_cast if
necessary.
* ExtendOp - zero- or sign-extending conversion from any integer type to
any wider integer type.
* TruncateOp - truncating conversion from any integer type to any
narrower integer type.
* PtrResizeOp - resizes a pointer without changing its pointee type.
Reject the `assignTypePunnedConstraint` DDR `Expressions.td` rewrite
when the `DstType` is an `ArrayType`, to avoid an invalid rewrite that
would violate the assumption that `bitcast`s do not admit a `ArrayType`
as `result` type.
Lauri Vasama