[PATCH] D104007: [BasicAA] Properly mark that coroutine suspension may modify parameters

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> However latter optimization passes could very well optimize out that copy because the copy would appear to be useless without considering what coro_suspend does, which is why we are changing BasicAA to prevent such elimination.

If an argument is just a pointer without any argument attributes, BasicAA will assume coro_suspend frees the underlying allocations.  Not because it has any particular knowledge of how coro_suspend works, but because that's the default assumption for any function call with unknown semantics.

BasicAA treats arguments marked byval differently because it understands the semantics of byval: it uses escape analysis to prove an arbitrary function call can't modify the contents.

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I guess in some sense, it's possible to specify a world where coro_suspend frees byval allocations.  But such a world doesn't really make sense.  And we'd need to audit every pass that knows anything about byval semantics, so I really don't want to go down that path.


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https://reviews.llvm.org/D104007