#[target_feature(enable="...")] does not enable use of feature-specific registers

[nagisa]

On x86 the following does not compile:

#![feature(asm)]

#[target_feature(enable="avx")]
pub unsafe fn foo() {
    let mut x = 0;
    asm!("vmovaps {}, {}", lateout(ymm_reg) x, in(ymm_reg) x);
}

ubt it does compile with -Ctarget-feature=+avx specified. Both should work?

[nagisa]

I don't think this needs to block the stabilization of the feature, however. Enabling this allows more programs to compile, not fewer.

[dobasy]

This compiles without attributes nor compiler options:

#![feature(asm)]

pub unsafe fn foo(a: &[u8; 32], b: &mut [u8; 32]) {
    asm!(
        "vmovups ymm0, ymmword ptr [{a}]",
        "vmovups ymmword ptr [{b}], ymm0",
        a = in(reg) a.as_ptr(),
        b = in(reg) b.as_mut_ptr(),
        out("ymm0") _,
    );
}

[nagisa]

Clobbers don't require a target feature. See also https://zulip-archive.rust-lang.org/stream/216763-project-inline-asm/topic/register.20class.20feature.20checks.html

[dobasy]

Isn't this clobber too?:

#![feature(asm)]

pub unsafe fn foo(a: &[u8; 32], b: &mut [u8; 32]) {
    asm!(
        "vmovups {ymm}, ymmword ptr [{a}]",
        "vmovups ymmword ptr [{b}], {ymm}",
        a = in(reg) a.as_ptr(),
        b = in(reg) b.as_mut_ptr(),
        ymm = out(ymm_reg) _,
    );
}

It doesn't compile.

[asquared31415]

@rustbot claim