[Mlir-commits] [mlir] [MLIR][LLVM] add metadata attrs and `llvm.named_metadata` op (PR #186703)

[Markus Böck]

zero9178 wrote:

> > not being able to model cyclic metadata at all (something that is not uncommon I believe?).
> 
> Interesting - not that I'm an `MDNode` afficianado but I was not aware of such a thing. Just out of curiosity, can you point me to an instance of this somewhere in LLVM?

`!llvm.loop` uses this (iirc as a workaround before distinct existed) + debug info uses this (think of debug info representing a C struct type containing a pointer to itself). 
You can write these yourself too: https://godbolt.org/z/sTrfhsrGh

Since we model all that LLVM-native metadata as MLIR attributes, only downstreams could possibly be affected and they should probably be "told" that cyclical structures are currently not supported.

https://github.com/llvm/llvm-project/pull/186703