Division by zero error when shifting right by the bit size of the result in Brillig

[ggiraldez]

Aim

Execute this program:

unconstrained fn main() {
    let a: u1 = 1 >> 1;
    assert(a == 0);
}

Expected Behavior

The execution completes successfully.

Bug

We get a runtime error:

error: Failed to solve brillig function, reason: Division by zero
  ┌─ /home/ggiraldez/Scratchpad/noir/bit_shifts_comptime/src/main.nr:2:22
  │
2 │     let a: u1 = 1 >> 1;
  │                      -
  │
  = Call stack:
    1. /home/ggiraldez/Scratchpad/noir/bit_shifts_comptime/src/main.nr:2:22

Failed to solve brillig function, reason: Division by zero

To Reproduce

Attempt to execute the given program.

Installation Method

Binary

Nargo Version

nargo version = 0.22.0 noirc version = 0.22.0+3fae4a03fded4e3f5065e7461c563f7e39745604 (git version hash: 3fae4a0, is dirty: false)

Additional Context

Removing the unconstrained keyword makes the program execute correctly, even when the input is not a constant to avoid optimizing away the operations.

The same error reproduces when changing the bit size of the variable along with the shifting amount, ie.: let a: u8 = 1 >> 8;

This was found while testing the debugger (which outputs Brillig by default) with the execution success case bit_shifts_comptime.

Would you like to submit a PR for this Issue?

No

Support Needs

No response

[TomAFrench]

Fixed in #4301