folkertdev wrote:
I believe this change is incomplete, consider
```rust
#![feature(c_variadic)]
#[unsafe(no_mangle)]
unsafe extern "C" fn foo(x: ...) -> u32 {
let mut x = core::hint::black_box(x);
let _ = unsafe { x.arg::<u32>() };
unsafe { x.arg::<u32>() }
}
#[unsafe(no_mangle)]
unsafe extern "C" fn bar() -> u32 {
foo(123u32, 456u32)
}
```
This currently produces
```asm
.type bar,@function
bar:
.functype bar () -> (i32)
.local i64, i32
global.get __stack_pointer
i64.const 16
i64.sub
local.tee 0
global.set __stack_pointer
local.get 0
i64.const 1958505087099
i64.store 0
local.get 0
call foo
local.set 1
local.get 0
i64.const 16
i64.add
global.set __stack_pointer
local.get 1
end_function
```
where `1958505087099` is `123 | 456 << 32`. In other words, the call itself
passes the arguments with a slot size of 4 as well.
I believe that the slot size is mostly relevant for aligning the values in the
variable arguments list. That might be less important for wasm, although the
alignment of 64-bit integers is 8 on the vast majority of host targets that
might run a wasm interpreter.
https://github.com/llvm/llvm-project/pull/173580
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