Closed
Description
On aarch64-unknown-linux-gnu (a tier 1 target), consider this testcase:
#![feature(rustc_attrs)]
type T = (f32, f32, f32);
#[repr(transparent)]
struct Wrapper2<T>((), T);
#[rustc_abi(debug)]
extern "C" fn test1(_x: T) {}
#[rustc_abi(debug)]
extern "C" fn test2(_x: Wrapper2<T>) {}
fn main() {}test1 passes its argument as
mode: Cast(
CastTarget {
prefix: [
None,
None,
None,
None,
None,
None,
None,
None,
],
rest: Uniform {
unit: Reg {
kind: Float,
size: Size(4 bytes),
},
total: Size(12 bytes),
},
attrs: ArgAttributes {
regular: (empty),
arg_ext: None,
pointee_size: Size(0 bytes),
pointee_align: None,
},
},
false,
),
test2 uses
mode: Cast(
CastTarget {
prefix: [
None,
None,
None,
None,
None,
None,
None,
None,
],
rest: Uniform {
unit: Reg {
kind: Integer,
size: Size(8 bytes),
},
total: Size(12 bytes),
},
attrs: ArgAttributes {
regular: (empty),
arg_ext: None,
pointee_size: Size(0 bytes),
pointee_align: None,
},
},
false,
),
IOW, test1 uses float registers and test2 uses int registers. This violates our promise that repr(transparent) types are ABI-compatible.
I think this might indicate a bug in the homogeneous_aggregate function? At least I don't see anything in the aarch64 adjustment that would be obviously wrong.