nargo debug does not follow natural order of program statements

[smanilov]

Aim

Consider the following program (lines indexed from 1):

fn main() {
    for i in 0..2 {
        println("---Test");
    }
}

Running nargo debug on this program, and stepping through it with next yields the following behavior:

1. cursor is pointing to line 1;
2. cursor is pointing to line 2, and highlighting i;
3. cursor is pointing to line 3, and highlighting the whole println expression;
4. cursor jumps back to line 2, highlighting 2, which is the boundary check of the loop;
5. cursor is pointing to line 2, and highlighting i;
6. cursor is pointing to line 3, and highlighting the whole println expression;
7. cursor is pointing to line 3, and highlighting the whole println expression;
8. cursor jumps back to line 4, highlighting nothing, which is the closing bracket of the loop body;
9. cursor jumps back to line 2, highlighting 2, which is the boundary check of the loop;
10. cursor is pointing to line 2, and highlighting i;
11. cursor is pointing to line 3, and highlighting the whole println expression;
12. cursor is pointing to line 3, and highlighting the whole println expression;
13. cursor jumps back to line 4, highlighting nothing, which is the closing bracket of the loop body;
14. cursor jumps back to line 2, highlighting 2, which is the boundary check of the loop;
15. cursor jumps back to line 5, highlighting nothing, which is the closing bracket of the function body; and
16. finished execution.

Expected Behavior

1. cursor is pointing to line 1;
   cursor is pointing to line 2, and highlighting i;
   cursor is pointing to line 3, and highlighting the whole println expression;
2. cursor is pointing to line 2, highlighting 2, which is the boundary check of the loop;
3. cursor is pointing to line 2, and highlighting i;
4. cursor is pointing to line 3, and highlighting the whole println expression;
5. cursor is pointing to line 3, and highlighting the whole println expression;
6. cursor jumps back to line 4, highlighting nothing, which is the closing bracket of the loop body;
7. cursor jumps back to line 2, highlighting 2, which is the boundary check of the loop;
8. cursor is pointing to line 2, and highlighting i;
9. cursor is pointing to line 3, and highlighting the whole println expression;
10. cursor is pointing to line 3, and highlighting the whole println expression;
11. cursor jumps back to line 4, highlighting nothing, which is the closing bracket of the loop body;
12. cursor jumps back to line 2, highlighting 2, which is the boundary check of the loop;
13. cursor jumps back to line 5, highlighting nothing, which is the closing bracket of the function body; and
14. finished execution.

Bug

In the observed behavior, the loop seems to be entered before the first boundary check is made.

To Reproduce

1. nargo new bug_example && cd bug_example
2. copy the source mentioned earlier in src/main.nr
3. run nargo debug and step through the program using next

Workaround

Yes

Workaround Description

Commenting out Ssa::loop_invariant_code_motion and Ssa::fold_constants from the list of performed optimizations and recompiling nargo leads to the expected behavior of nargo debug.

P.S., disabling just Ssa::loop_invariant_code_motion leads to a different behavior of nargo debug, but it is still not the naturally expected one. Let me know and we can file a separate issue.

Additional Context

No response

Project Impact

Blocker

Blocker Context

Our project (a debugger GUI) depends on the natural behavior of nargo debug.

Nargo Version

nargo version = 1.0.0-beta.2 noirc version = 1.0.0-beta.2+b7ace682af1ab8a43308457302f08b151af342db (git version hash: b7ace68, 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