Think about removal of custom TypeTraits

[Jezurko]

Prerequisites

• I have read the documentation and the proposed feature is not implemented.

Description

Currently, we have several custom type traits (in include/vast/Dialect/Core/Utils.td and include/vast/Dialect/Core/TypeTraits.hpp) to generate traits for Operation verifiers.
E.g.

class IsPointer< string arg > : PredOpTrait< "value is of a pointer type",
    CPred< "$" # arg # ".getType().hasTrait< mlir::TypeTrait::PointerTypeTrait >()" >
>;

and(CORE_TRAIT is our own macro):

CORE_TRAIT(PointerTypeTrait);

and adding the trait to the relevant types (in this case PointerType and DecayedType).

Instead, we could have (in include/vast/Dialect/Highlevel/HighlevelTypes.td):

class IsPointer< string arg > : PredOpTrait< "IsTypedef",
  SubstLeaves< "$_self", "$" # arg #".getType()", Or< [PointerType.predicate, DecayedType.predicate] > >
>;

without any additional code.

Advantages:

• Reduced amount of code
• It can be defined within the related dialect
• To me it seems a bit more uniform with how the rest of the verification is done
• I vaguely remember, that having to write the C++ code (in TypeTraits.hpp) might be problematic for dynamic dialects or something like that (@xlauko might remember more?)

Disadvantages:

• TypeTraits are a bit more flexible (anyone can pass their type into our operations by adding the trait to it)
• TypeTraits can be used by multiple dialects in VAST (although I don't believe that's the case right now)
• The information about the predicate is further from the type itself