erichkeane added a comment.
In https://reviews.llvm.org/D45383#1061780, @efriedma wrote:
> Identical to what? `__builtin_va_start` and `__builtin_va_end` specifically
> are weird because they're builtins which have a signature which can't be
> expressed in C. vprintf doesn't have that problem.
> Builtins.def makes the relevant distinction already: a "BUILTIN" is a
> reserved identifier the user isn't allowed to redeclare, and a "LIBBUILTIN"
> is a library function which the compiler has special knowledge of.
In the context of this patch, vprintf is handled using the exact same
code-paths. SO, it'll have its 2nd parameter created with type 'char*&', which
can cause the same crash that I observed with overloading va_end. Currently,
you ARE permitted to redeclare a BUILTIN (see my 1st test above), but a
conflicting type is an error. A LIBBUILTIN is a warning to have a conflicting
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