Inline asm!() with "i" constraint produces the wrong assembly due to (now-fixed) LLVM bug

[stevecheckoway]

Nightly rustc correctly handles the first of these two inline assembly statements but silently does the wrong thing with the second one (example on Compiler Explorer).

#![feature(asm)]
static FOO: usize = 0;

pub unsafe fn example() {
    asm!("movq $0, %rax" :: "i"(&FOO) :: "volatile");
    asm!("mov rbx, $0" :: "i"(&FOO) :: "intel", "volatile");
}

The issue is LLVM's call asm inteldialect had a bug that was fixed. I think the solution is to cherry-pick the LLVM fix.

You can see the problem directly using LLVM IR here.

[Amanieu]

This issue does not apply to the new asm! (RFC 2850) which uses sym operands. Note that sym operands only produce the raw symbol name, you are responsible for adding offset as needed.

The legacy llvm_asm! is deprecated and is no longer maintained.

[stevecheckoway]

Thanks. I'll take a look at the new asm!.

[Amanieu]

I believe we got the LLVM bug fix when we upgraded to LLVM 10.