Tail recursion warning and attribute, take 3

[dawedawe]

This is an alternative approach to #15260 (RFC1011)
Instead of operating in PostInferenceChecks.fs this PR is using the IL level to emit warnings.
It seems a lot easier to emit warnings from there, but this approach currently suffers from a lot of false positives as can be seen in the tests.

• Identify calls from outside the rec def, so we don't emit false positives
• Identify rewrites to loops, so we don't emit false positives

[vzarytovskii]

Haven't reviewed it in detail yet, however, the first thouhg is that ilxgen doesn't feel like the right place for doing the tailcall analysis.

The analysis happens when we emit call(virt)s, which is orthogonal to the F#'s (tail) recursion (when we unroll recursion to loops, etc).

[dawedawe]

Haven't reviewed it in detail yet, however, the first thouhg is that ilxgen doesn't feel like the right place for doing the tailcall analysis.

The analysis happens when we emit call(virt)s, which is orthogonal to the F#'s (tail) recursion (when we unroll recursion to loops, etc).

@vzarytovskii Thanks for your thoughts on this.
Yeah, I'm struggling a bit with finding the right place which provides the needed information.
Can you point me into some direction? Should it all be done in the optimizer?

[vzarytovskii]

Haven't reviewed it in detail yet, however, the first thouhg is that ilxgen doesn't feel like the right place for doing the tailcall analysis.
The analysis happens when we emit call(virt)s, which is orthogonal to the F#'s (tail) recursion (when we unroll recursion to loops, etc).

@vzarytovskii Thanks for your thoughts on this. Yeah, I'm struggling a bit with finding the right place which provides the needed information. Can you point me into some direction? Should it all be done in the optimizer?

That's a good question, I would think that post inference phase, or optimization phase are the most fitting ones.

[dawedawe]

For those following along, I thing this PR is superseded by #15503
Please go there for the lastest work.