newruntime and computed goto: variables inside the loop are in generated code uninitialised

[RSDuck]

Here's an example:

Example

proc test(a: range[0..1]) =
    while true:
        {.computedGoto.}
        
        let b = int(a) * 2

        case a
        of 0:
            echo b
            break
        of 1:
            echo b
            break

test(1)

The reason for this is that in C code b is always redefined, for each individual case. This is the reason the value assigned to b during the previous iteration is lost.

Current Output

This can vary based on what's still in register/memory

42

Expected Output

2

Additional Information

Nim Compiler Version 1.1.1 [Windows: amd64]
Compiled at 2019-11-29
Copyright (c) 2006-2019 by Andreas Rumpf

git hash: c5c6bae2a42734df2ba5fdb7cd8cf327d4e7005f
active boot switches: -d:release

[Araq]

Is this related in any way to --newruntime? Cause it looks like it isn't.

[RSDuck]

yes, atleast I think so. If you compare the generated code without newruntime enabled, you see that b is only declared once, while it is declared multiple times with newruntime enabled.

I'm still using the same git revision as in the original post.