TTIR constant materialization

[azecevicTT]

ConstantOp in the TTIR dialect has a ConstantLike trait so constants can be materialized into ttir.constant operation. We already have one use case, where GetDimensionSizeOp is folded into Attribute, so instead of decomposition, a folding into Attribute and materialization into ConstantOp takes a more natural approach.

For all future use cases of FooOpToConstantOp conversions, instead of implementing pattern rewriting, it's enough to fold FooOp into mlir::ElementsAttr.

[mrakitaTT]

Nice, thanks for adding this! I've planned to do this long time ago but wasn't sure if that will do the trick without other changes to enable canonicalization. I also wasn't sure if we can rely that folders will always be activated during compilation and remove explicit conversions, mlir documentation wasn't very helpful on this, did you find a confirmation somewhere?

[azecevicTT]

Nice, thanks for adding this! I've planned to do this long time ago but wasn't sure if that will do the trick without other changes to enable canonicalization. I also wasn't sure if we can rely that folders will always be activated during compilation and remove explicit conversions, mlir documentation wasn't very helpful on this, did you find a confirmation somewhere?

@mrakitaTT Yeah, I had to dive into MLIR's source code, during legalization it first tries with fold, and only then try with patterns as a fallback.
https://mlir.llvm.org/doxygen/DialectConversion_8cpp_source.html : 2033.

[sdjordjevicTT]

Great change!

[nsmithtt]

This looks great! Perhaps we can add a test that exercises this case?

[azecevicTT]

@nsmithtt There are already some tests that cover get_dimension_size_op conversions, though none of them cover ttir.get_dimension_size -> ttir.constant directly, they all go ttir.get_dimension_size -> ttnn.full where ttir.constant is the intermediate step. Thanks for pointing that out, I will add it soon.