Test closures_mut_ref fails with inliner <= 0 and brillig

[aakoshh]

Aim

Trying to run test_programs with different --inliner-aggressiveness in #6429

Expected Behavior

Tests under execution_success should work.

Bug

❯ nargo execute --force --inliner-aggressiveness 0 --force-brillig
error: Failed to solve program: 'Failed to solve brillig function'
   ┌─ /Users/aakoshh/Work/aztec/noir/test_programs/execution_success/closures_mut_ref/src/main.nr:23:12
   │
23 │     assert(*x1 == 44);
   │            ---------
   │
   = Call stack:
     1. /Users/aakoshh/Work/aztec/noir/test_programs/execution_success/closures_mut_ref/src/main.nr:14:5
     2. /Users/aakoshh/Work/aztec/noir/test_programs/execution_success/closures_mut_ref/src/main.nr:23:12

Failed to solve program: 'Failed to solve brillig function'

To Reproduce

1. cd test_programs/execution_success/closures_mut_ref
2. nargo execute --force --force-brillig --inliner-aggressiveness 0 or
3. nargo execute --force --force-brillig --inliner-aggressiveness -9223372036854775808

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

None

Blocker Context

No response

Nargo Version

nargo version = 0.36.0 noirc version = 0.36.0+2f0cb3e80f3d93a1dee77fffacc397811e300257 (git version hash: 2f0cb3e, is dirty: false)

NoirJS Version

No response

Proving Backend Tooling & Version

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response

[aakoshh]

The problem indeed seems to be the same as #6443

Reduced the test program to be just the following:

fn main(mut x: Field) {
    issue_2120();
}
fn issue_2120() {
    let x1 = &mut 42;
    let set_x1 = |y| { *x1 = y; };
    set_x1(44);
    assert(*x1 == 44);
}

The test fails at the assertion. Looking at the SSA, we can see that the f2 function representing the set_x1 lambda gets its body eliminated:

❯ cargo run -q -p nargo_cli --  --program-dir . execute --force --force-brillig --inliner-aggressiveness -9223372036854775808 --show-ssa
Initial SSA:
brillig(inline) fn main f0 {
  b0(v0: Field):
    v1 = allocate
    store v0 at v1
    call f1()
    return 
}
acir(inline) fn issue_2120 f1 {
  b0():
    v0 = allocate
    store Field 42 at v0
    call f2(v0, Field 44)
    v4 = load v0
    v5 = eq v4, Field 44
    constrain v4 == Field 44
    return 
}
acir(inline) fn lambda f2 {
  b0(v0: &mut Field, v1: Field):
    v2 = allocate
    store v0 at v2
    v3 = load v2
    store v1 at v3
    return 
}

...

After Array Set Optimizations:
brillig(inline) fn main f0 {
  b0(v0: Field):
    call f1()
    return 
}
brillig(inline) fn issue_2120 f1 {
  b0():
    v0 = allocate
    store Field 42 at v0
    call f2(v0, Field 44)
    v4 = load v0
    constrain v4 == Field 44
    return 
}
brillig(inline) fn lambda f2 {
  b0(v0: &mut Field, v1: Field):
    return 
}

[aakoshh]

Fixed by #6452