Inline `asm!` is unnecessarily duplicated

[ChrisDenton]

The following example code:

unsafe extern "system" {
    safe fn finish_ffi_stuff(handle: isize) -> bool;
    safe fn do_ffi_stuff(path: *const u8) -> isize;
    safe fn get_ffi_result() -> u32;
}

//#[inline(never)]
fn get_result() -> u32 {
    let code: u32;
    #[cfg(target_arch = "x86_64")]
    unsafe {
        core::arch::asm!(
            "call {}", // yes, I know. this is just an example.
            sym get_ffi_result,
            out("eax") code,
            options(nostack, preserves_flags, pure, readonly)
        );
    }
    code
}

fn finish_stuff(handle: isize) -> Result<(), u32> {
    match finish_ffi_stuff(handle) {
        false => Err(get_result()),
        true => Ok(())
    }
}

fn do_stuff(path: &str) -> Result<isize, u32> {
    let handle = do_ffi_stuff(path.as_ptr());
    match handle {
        -1 => Err(get_result()),
        _ => Ok(handle)
    }
}

pub fn my_main() -> u32 {
    match do_stuff("meow") {
        Ok(meow) => finish_stuff(meow).err().unwrap_or(0),
        Err(e) => e
    }
}

Produces the following x86_64 assembly:

example[46d8dd5c5912c656]::my_main:
        push    rax
        lea     rdi, [rip + .Lanon.014ce376276f773fc8cbe61d4d1296c1.0]
        call    qword ptr [rip + do_ffi_stuff@GOTPCREL]
        cmp     rax, -1
        je      .LBB0_3
        mov     rdi, rax
        call    qword ptr [rip + finish_ffi_stuff@GOTPCREL]
        test    al, al
        je      .LBB0_4
        xor     eax, eax
        pop     rcx
        ret
.LBB0_3:

        call    get_ffi_result

        pop     rcx
        ret
.LBB0_4:

        call    get_ffi_result

        pop     rcx
        ret

.Lanon.014ce376276f773fc8cbe61d4d1296c1.0:
        .ascii  "meow"

Note that .LBB0_3 and .LBB0_4 are exact duplicates. While the compiler can't see inside asm blocks, I'd assume it at least knows that they are the same in this case.

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rustc --version --verbose:

rustc 1.94.0-nightly (ba86c0460 2025-12-06)
binary: rustc
commit-hash: ba86c0460b0233319e01fd789a42a7276eade805
commit-date: 2025-12-06
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.5