This is part of the RFC for a better fold API: https://discourse.llvm.org/t/rfc-a-better-fold-api-using-more-generic-adaptors/67374
This patch implements the required foldHook changes and the TableGen machinery for generating `fold` method signatures using `FoldAdaptor` for ops, based on the value of `useFoldAPI` of the dialect. It may be one of 2 values, with convenient named constants to create a quasi enum. The new `fold` method will then be generated if `kEmitFoldAdaptorFolder` is used.
Since the new `FoldAdaptor` approach is strictly better than the old signature, part of this patch updates the documentation and all example to encourage use of the new `fold` signature.
Included are also tests exercising the new API, ensuring proper construction of the `FoldAdaptor` and proper generation by TableGen.
Differential Revision: https://reviews.llvm.org/D140886
This moves the documentation for defining dialects, attributes/types,
and operations into a new `DefiningDialects` folder. This helps to
keep the documentation grouped together, making it easier to find
related documentation.
Differential Revision: https://reviews.llvm.org/D137594
