PDL API

[raviqqe]

Problem

• We don't have the PDL API.
  • PDL dialect is not implemented yet.
  • But it should be available and easy to implement through the usual operation construction API.

Solution

Proposing the C API for PDL

• Implementation by @Danacus
  • https://gitlab.com/Danacus/mlir-sys/-/commit/bdf751a53d2c2e096a6b10fcfe39bcf8071c1add
  • https://gitlab.com/Danacus/melior/-/commit/cf482208af5e48a563e6e88db151ef716e11f379#fcb791682a2fbacc880e6e3086d9340c202a4ab6

Extending mlir-sys

TBD

References

• The original discussion is in ExternalPass API #248.

[Danacus]

We don't really need PDL dialect constructors, since PDL patterns can be written in PDLL and can be converted to the PDL dialect with mlir-pdll.

I think we should either request additions to the C API upstream in MLIR, or implement them in a separate crate with API extensions.

Some additional considerations:

• How expressive is the pdl dialect (or pdl-interp)? Are there patterns that can only be expressed using C++ RewritePatterns? If so, would it be useful to be able to write such patterns in Rust?
• Would it be useful to expose an API in MLIR to compile PDLL and avoid needing to run the mlir-pdll command?

[Danacus]

I've submitted a revision to LLVM: https://reviews.llvm.org/D156021

[raviqqe]

Thank you so much!