Unsigned integer division doesn't work with --experimental-ssa

[shuklaayush]

Aim

use dep::std::println;

#[test]
fn test_div() {
    let a: u16 = 5;
    let b: u16 = 2;

    let c = a / b;

    // 0x183227397098d014dc2822db40c0ac2e9419f4243cdcb848a1f0fac9f8000003
    println(c);
    // This fails
    assert(c == 2);
}

Expected Behavior

The test should pass

Bug

Dividing unsigned ints with --experimental-ssa seems to calculate multiplication with the field inverse instead of standard integer division

To Reproduce

1. Copy the above code
2. Run the test

nargo test --show-output --experimental-ssa

Installation Method

Compiled from source

Nargo Version

nargo 0.8.0 (git version hash: 4969da7, is dirty: false)

Additional Context

No response

Would you like to submit a PR for this Issue?

Maybe

Support Needs

No response

[kevaundray]

Thanks for opening this issue and bring it up on the call!

The bug is in this function:

noir/crates/noirc_evaluator/src/ssa_refactor/ir/instruction.rs

Line 771 in 4969da7

fn eval_constants(

When we have instructions with constant values, they get simplified on the fly. The problem is that our simplification pass is not taking into consideration the type. See division where it is doing lhs / rhs where these are FieldElements.

This method should be modified to check if we want to do field arithmetic or integer arithmetic and evaluate the constant expression accordingly.

Note: that this will only fail for constants. Non-constants won't be simplified and we do the division via acir_gen.