Rust inline asm with generics and macros builds using --release, fails in debug

[danlehmann]

I tried this code:

use std::arch::{asm, global_asm};

global_asm!("
.macro test
.endm
");

fn function<const N: u32>() {
    unsafe {
        asm!("test", options(noreturn))
    }
}

fn main() {
    function::<1>()
}

I expected to see this happen: This code should work when compiling for release and debug.

Instead, this happened: It builds fine using --release. In debug mode, the inline assembler can't see the macro test.

I'd expect that either both Debug and Release work or that both fail equally.

~/CLionProjects/untitled1 % cargo run                                                   
   Compiling untitled1 v0.1.0 (/Users/daniel/CLionProjects/untitled1)
error: unrecognized instruction mnemonic, did you mean: tst?
  --> src/main.rs:11:15
   |
11 |         asm!("test", options(noreturn))
   |               ^
   |
note: instantiated into assembly here
  --> <inline asm>:1:2
   |
1  |     test
   |     ^

error: could not compile `untitled1` due to previous error



~/CLionProjects/untitled1 % cargo run --release
   Compiling untitled1 v0.1.0 (/Users/daniel/CLionProjects/untitled1)
    Finished release [optimized] target(s) in 0.10s
     Running `target/release/untitled1`

Meta

rustc --version --verbose:

rustc 1.68.0-nightly (3020239de 2023-01-09)
binary: rustc
commit-hash: 3020239de947ec52677e9b4e853a6a9fc073d1f9
commit-date: 2023-01-09
host: aarch64-apple-darwin
release: 1.68.0-nightly
LLVM version: 15.0.6

[asquared31415]

@rustbot label +A-inline-assembly

I did some poking and it seems to be tied to the presence of the -C incremental flag, which is passed by default in the default cargo debug profile.

[asquared31415]

oh this is an example of how #81838 can break

[Amanieu]

This is explicitly not supported by inline assembly:

If inline assembly includes any "stateful" directive that modifies how subsequent assembly is processed, the block must undo the effects of any such directives before the inline assembly ends.

Basically you can't rely on things defined in other asm blocks.