Loops with zero trip count trigger an internal error when run on the GPU about chapel

[ShreyasKhandekar]

I have the PR linked above that adds an if statement to avoid the kernel launch. I did not make any changes to the GPU diagnostics yet.

[stonea]

A question that we should answer is whether GpuDiagnostics should register a loop like that as a kernel launch, or not. My initial reflex was that "Yes, it should."

My initial reflex would be the opposite. If we're not launching a kernel then why would we count it as a kernel launch?

[bradcray]

I agree with Andy. I think if we squash the launch into (effectively) a no-op, it should not be counted since it suggests an overhead or cost that isn't actually being incurred and can't be further optimized away.

[e-kayrakli]

I agree with Andy and Brad -- it should not count as a launch.

My point in the OP:

Imagine a hypothetical scenario where we may choose between GPU/CPU execution based on some loop characteristic either statically or dynamically potentially as an optimization. In such a scenario, I would want GpuDiagnostics to reflect the actual behavior.

Resonated more and more over time for me. My slightly more practical thought experiment for this case was: imagine we have an optimization where we don't fire kernels for loops that trip less than 10 times. What do you expect GpuDiagnostics to do in that case? My answer to that is very clear and that it should not count that as a launch.