[PATCH] D132952: [Sema] disable -Wvla for function array parameters

[Eli Friedman via Phabricator via cfe-commits]

efriedma added a comment.

In D132952#3759226 <https://reviews.llvm.org/D132952#3759226>, @aaron.ballman wrote:

>> We could theoretically mess with the AST representation somehow, but I don't see any compelling reason to.  We probably just want to emit the warn_vla_used diagnostic somewhere else.
>
> Yeah, re-reading the C standard, I think I got VM types slightly wrong. Consider:
>
>   void func(int n, int array[n]);
>
> `array` is a VLA (C2x 6.7.6.2p4) before pointer adjustment (C2x 6.7.6.3p6), which makes `func` a VM type (C2x 6.7.6p3), not `array`.

The type of parameter array after promotion (which is the type that matters for almost any purpose), is `int*`.  That isn't variably modified.  And the function type is just `void(int,int*)`; there's no way we can possibly treat that as variably modified.

If you wrote, say `void func(int n, int array[n][n])`, then array is variably modified.  "func" is still not variably modified, I think?  "array" is not part of the "nested sequence of declarators", despite the fact that the parameter list contains a variably modified type.  At least, that's clang's current interpretation of the rules.


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https://reviews.llvm.org/D132952