[PATCH] D62319: IR: add 'size <N>' attribute to 'byval' function parameters

[Tim Northover via Phabricator via llvm-commits]

t.p.northover added a comment.

> One of the other suggestions was to pass a _type_ as a parameter to byval. IMO that would be the nicest idea (but I don't know if it's infeasibly difficult?)

I wouldn't worry about the implementation difficulty, I can see a pretty clear path there. I also like the spelling of that option, it certainly bypasses the ambiguity of a bare number. I wonder if it's promising more than we actually deliver though. SelectionDAG only exposes the size and alignment to backends.

A final point in favour of the type idea is that I think targets where pointers are special (e.g. CHERI where a pointer in memory is only usable if it was stored by a special, blessed instruction) couldn't work with a plain size. They don't work with SelectionDAG either but in future they might want to use byval. I'm not entirely sure how theoretical that argument is though.


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  https://reviews.llvm.org/D62319/new/

https://reviews.llvm.org/D62319