[llvm] [mlir] [NFC][mlir][NVVM] Move op descriptions to NVVMOpsDoc.td (PR #225090)

[Rajat Bajpai via llvm-commits]

rajatbajpai wrote:

> I'm wondering why do we add indirection to docs? When I look at the OP, it love to see it's description as well

I agree with your point. I also prefer keeping an op's description inline where possible. However, some op descriptions are long enough to make the op definition, including its interface and other details, harder to read.

For such ops, I think it would be useful to have an alternative mechanism that keeps the description separate without muddying the op definition. This would **not replace the existing inline-description approach**, which may still be preferable for simpler ops with shorter descriptions.

Reducing the size of the monolithic `NVVMOps.td` file is not the main motivation for this approach, but it would also be a useful side effect, given that the file is approaching ~8K lines.

https://github.com/llvm/llvm-project/pull/225090