A let variable, initialized with a mutable variable behaves as an alias: it changes after change in the mutable variable: possible ssa regression

[alehander92]

Aim

We were trying to make our closure reforms PR pass the old higher_order_functions tests, and it seemed it didn't work with the alias of a mutable variable case: however it seems it is because this behavior changed

a minimal example is

use dep::std;

fn main() -> pub Field {
    let mut x = 2;
    let z = x;

    x = x + 1;
    assert(z == 2);
    x
}

Expected Behavior

Circuit witness successfully solved
Circuit output: Field(2)

Bug

instead we get

error: 
  ┌─ /home/al/noir/a/src/main.nr:8:12
  │
8 │     assert(z == 2);
  │            ------ Failed constraint

and an assert(z == 3) passes instead:

it seems, it worked as expected with the original ssa backend(tested before rebasing on a commit that drops it)

To Reproduce

write down a program like

use dep::std;

fn main() -> pub Field {
    let mut x = 2;
    let z = x;

    x = x + 1;
    assert(z == 2);
    x
}

and run it with

nargo execute

Installation Method

Compiled from source

Nargo Version

nargo 0.9.0 (git version hash: 0189e270bc6c15c26d3197400e76ef74ec285c6a, is dirty: true)

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response