[PATCH] D130224: [Clang][Attribute] Introduce maybe_undef attribute for function arguments which accepts undef values

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added a comment.

In D130224#3677224 <https://reviews.llvm.org/D130224#3677224>, @aaron.ballman wrote:

> However, what I think I'm hearing from this thread is that there are alternative approaches that have been thought about but not tried, we're not certain how feasible those approaches are in practice, but we expect them to be materially worse than what's proposed here. So it's not "this was the path of least resistance", but "this is the correct design." Do others agree with that assessment?

I think this is just the least bad on the menu of available options. I don't like it, but it at least provides documentation about this special behavior.

I think the only other plausible option is to assert this is still undefined behavior and force users to update their (newly declared invalid) code. We could at least partially re-optimize to uninitialized values in the backend (although this is apparently difficult in some situations)


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