Bug 18274 – va_arg (TypeInfo) broken for static arrays

This code is currently broken: https://run.dlang.io/is/68hf1w --------------------------------------------- void foo(...) { uint[4] data; va_arg(_argptr, _arguments[0], &data); //data = va_arg!(uint[4])(_argptr); writeln(data); } void main() { uint[4] value = [1, 2, 3, 4]; foo(value); } --------------------------------------------- [4, 0, 3567405808, 32767] The commented, static variant works. The problem is that DMD passes static arrays as {.ptr, .length} slice with TypeInfo_Tuple for D variadic functions. va_arg would have to detect this and instead of just copying the data it has to dereference the pointer. I'm not sure if this is easily possible though: DMD passes TypeInfo_Tuple instead of TypeInfo_StaticArray. Can TypeInfo_Tuple only occur for static arrays? If so, fixing this is easy. If not, we have to pass proper TypeInfo for static array parameters. I don't know why we even do this, at least on AArch64 we can have much better performance by just passing static arrays by value in the same way a struct would be passed. Passing as ptr+length requires another special case in the va_arg function for static arrays.

OK, I see that my assumption to get out exactly the same type as passed in was flawed. If you strictly interpret the passed arguments according to _arguments, the type of the data changed from static to dynamic array, but the data is still correct. So this is not really a bug.