[llvm] [MISched] Fix off-by-one error with -misched-cutoff=<n> flag (PR #137988)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

> The "Scheduling SU" message you grep-ed was from `pickNode`. The reason you saw 11 messages when the cut-off was 10 is because `checkSchedLimit` is placed _after_ `pickNode`:
> 
> https://github.com/llvm/llvm-project/blob/fa769655e73d70b480be8034a1cbc101115c1678/llvm/lib/CodeGen/MachineScheduler.cpp#L1007-L1012
> 
> So basically what happened was that although it showed 11 "Scheduling SU", the scheduler indeed only scheduled 10 instructions as it stopped right before it made any actual changes.
> 
> Therefore, following the same logic, I think your current patch will actually scheduled one _less_ instruction then the cut-off value provided by the user, which is probably undesired.
> 
> I think a better solution might be putting `checkSchedLimit` before `pickNode`.

ah, well spotted! Thanks that makes more sense, updated 👍 

https://github.com/llvm/llvm-project/pull/137988