Call arguments are evaluated right to left on x86

[u7k4rs6]

Summary

On x86 we evaluate function arguments right to left, but Rust evaluates them left to right. Method calls and overloaded operators go through the same path, so a() + b() on a user type runs b() first too. The gimplifier evaluates call arguments in the target's push order, which is reversed on x86.

Reproducer

I tried this code:

#![feature(no_core)]
#![no_core]

static mut N: i32 = 0;

fn tick() -> i32 {
    unsafe {
        N += 1;
        N
    }
}

fn three(a: i32, b: i32, c: i32) -> i32 {
    a * 100 + b * 10 + c
}

fn main() -> i32 {
    // rustc gives 123
    three(tick(), tick(), tick()) - 123
}

Does the code make use of any (1.49) nightly feature ?

• Nightly

Godbolt link

No response

Actual behavior

three gets 3, 2, 1, so the program exits with a non-zero code.

Expected behavior

three gets 1, 2, 3 and the program exits with 0.

GCC Version

36b5a15