Packed struct

[antoyo]

No description provided.

[bjorn3]

I think this is already supported. For

#[repr(packed)]
pub struct Foo(u8, u64, u64);

pub fn foo(v: Foo) -> Foo {
    v
}

//#[repr(packed)]
pub struct Bar(u8, u64, u64);

pub fn bar(v: Bar) -> Bar {
    v
}

the only difference between cg_llvm and cg_gcc seems to be different register selection choices, different instruction ordering and gcc using a potentially more efficient instruction for loading a single byte.

https://rust.godbolt.org/z/xdfKxo3v1

[antoyo]

Are you sure that if you have such a struct in memory, it will have the correct size?

I thought it's not supported because I don't set the __packed__ attribute.

[bjorn3]

I checked that statics work correctly: https://rust.godbolt.org/z/W9j1Y3j7M

Locals however don't work correctly:

#[repr(packed)]
pub struct Foo(u8, u64, u64);

pub fn foo(mut v: Foo) -> Foo {
    v.0 += 1;
    v.1 += 2; // cg_gcc uses offset 8 here while cg_llvm uses offset 1
    v
}

//#[repr(packed)]
pub struct Bar(u8, u64, u64);

pub fn bar(mut v: Bar) -> Bar {
    v.0 += 1;
    v.1 += 2;
    v
}

https://rust.godbolt.org/z/abEnddxbj

[bjorn3]

Fixed by #148, right?