794457f6f9
Pass variadic arguments without changing their type, unlike the fixed ones. Fixed arguments are modified to better fit into registers. This patch leaves those unchanged. Splitting struct types into individual fields and packing small structs into integers works well for passing via registers. Variadic arguments are currently unimplemented in the backend. They're likely to be implemented as a pointer to stack memory in which case register-themed optimisations are inapplicable. Splitting the struct into fields makes it difficult to implement va_arg robustly. The rules around padding and alignment to inverse the struct splitting could be constructed, but at high complexity and no particular advantage. Passing types as-is means there is a 1:1 correspondence with the type information va_arg has to work with and the parameter type at the call site. This is an ABI change, but as the only functions affected are variadic ones which are presently a compilation error, not a functional break. Factored out of the larger #93362 and can land independently.
13 KiB
13 KiB