[PATCH] D103275: Update musttail verification to check all swiftasync->swiftasync tail calls.

[Duncan P. N. Exon Smith via Phabricator via llvm-commits]

dexonsmith added a subscriber: rjmccall.
dexonsmith added a comment.

In D103275#2785679 <https://reviews.llvm.org/D103275#2785679>, @dexonsmith wrote:

> I guess I'm wondering what the trajectory is - if the goal is for this to eventually be an IR invariant for the calling convention, I think a verifier check makes sense; once the codegen bugs are sorted out, and the bitcode upgrade is done, the flag can be switched to on-by-default and eventually removed. But if this will never be an invariant of the IR, I'm not sure the LLVM IR verifier is really the right place for the check.

Ah, I see you've already answered that:

>> Is the goal to eventually have it on always in the fullness of time?
>
> Ideally yes. There shouldn't be a good reason for us to miss musttail on tail calls like this one.

In that case, should this patch also document the intended invariant (maybe with a caveat that it's not enforced yet?) at the swifttailcc entry in LangRef? (https://llvm.org/docs/LangRef.html#calling-conventions)

@rjmccall , I'd be curious about your thoughts.

(Just to explain the other option on my mind -- if this isn't an IR invariant for the calling convention, just a linting check for IR with bad style, maybe there should be a separate pass for linting, and we keep the verifier focused on whether IR is valid.)


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https://reviews.llvm.org/D103275