[llvm] [GISel] Add debug counter to force sdag fallback (PR #78257)

[Nikita Popov via llvm-commits]

nikic wrote:

> When I did the daemon based bisector a few years back I had to put the fallback trigger in the InstructionSelect pass, since it's possible to fall back naturally all the way through the pipeline. That is if you want to trigger after exactly _N_ GISel functions compiled.

So in the current implementation, we would fall back after N functions (regardless of whether they would have fallen back anyway), while doing it in InstructionSelect means we would fall back after N functions that would have otherwise succeeded GlobalISel, right?

I don't really have a strong opinion on either of those choices -- I think for bisection purposes it wouldn't really matter.

https://github.com/llvm/llvm-project/pull/78257