[llvm] [CodeGen][MISched] Handle empty sized resource usage. (PR #75951)

[Francesco Petrogalli via llvm-commits]

fpetrogalli wrote:

I actually have another question, which challenges this design:

> TargetSchedule.td explicitly allows the usage of a ProcResource for zero cycles, in order to represent that the ProcResource must be available but is not consumed by the instruction. 

Why is this allowed? And where is this specified? I could not find any reference of this in TargetSchedule.td

It seems to me that, if a resource is required to be available, it means that the instruction needs to use it? Why not just mark it for  at least 1 cycle usage?

Francesco

https://github.com/llvm/llvm-project/pull/75951