[ER] One useless division by zero test

[leonardo-m]

This is an enhancement request. This program scans every possible input for the foo function, showing it never gives a division by zero error:

type T = u16;

#[inline(never)]
pub fn foo(x: T, y: T) -> T {
    if x > y {
        100 / (x - y)
    } else {
        100
    }
}

fn main() {
    let mut tot: T = 0;
    for x in T::MIN ..= T::MAX {
        for y in T::MIN ..= T::MAX {
            tot = tot.wrapping_add(foo(x, y));
        }
    }
    println!("{}", tot);
}

But LLVM adds an useless division by zero test (the same happens for T = u32):

foo:
    mov     ax, 100
    sub     di, si
    jbe     .LBB0_3
    je      .LBB0_4
    mov     ax, 100
    xor     edx, edx
    div     di
.LBB0_3:
    ret
.LBB0_4:
    push    rax
    lea     rdi, [rip + str.0]
    lea     rdx, [rip + .L__unnamed_1]
    mov     esi, 25
    call    qword ptr [rip + core::panicking::panic@GOTPCREL]
    ud2

[leonardo-m]

The problems is still present in LLVM V.11.

[nikic]

Godbolt: https://rust.godbolt.org/z/6cWWYvWcr Still present.

[MSxDOS]

LLVM 13 - no change.
No such failure with GCC: https://godbolt.org/z/5jGWfGc7z

[workingjubilee]

Leaving this open because clang trunk fixes this: https://godbolt.org/z/f516vsxd7

[veera-sivarajan]

Fixed since rustc 1.65.0: https://rust.godbolt.org/z/dTxdorYz3

@rustbot label +llvm-fixed-upstream +E-needs-test