Const i32 expressions do not support integer div/mod operations

[dylon]

I have the following source:

# path: /var/tmp/lp/qux.py
from lpython import Const, i32
foo: Const[i32] = 4
bar: Const[i32] = foo // 2

running it through lpython breaks with the following error:

$ ~/Workspace/lpython/src/bin/lpython /var/tmp/lp/qux.py
semantic error: Arguments do not match for any generic procedure, _lpython_floordiv
 --> /var/tmp/lp/qux.py:4:19
  |
4 | bar: Const[i32] = foo // 2
  |                   ^^^^^^^^


Note: Please report unclear or confusing messages as bugs at
https://github.com/lcompilers/lpython/issues.

This should be supported, especially since lpython does not complain about multiplication:

# path: /var/tmp/lp/qux.py
from lpython import Const, i32
foo: Const[i32] = 4
bar: Const[i32] = foo * 2

def main() -> None:
    print(foo)
    print(bar)

main()

$ ~/Workspace/lpython/src/bin/lpython /var/tmp/lp/qux.py
4
8

The following does work, but is ugly:

# path: /var/tmp/lp/qux.py
from lpython import Const, i32
foo: Const[i32] = 4
bar: Const[i32] = i32(foo / 2)

def main() -> None:
    print(foo)
    print(bar)

main()

$ ~/Workspace/lpython/src/bin/lpython /var/tmp/lp/qux.py
4
2

Note that mod (%) also does not work:

$ cat /var/tmp/lp/qux.py
# path: /var/tmp/lp/qux.py
from lpython import Const, i32
foo: Const[i32] = 4
bar: Const[i32] = foo % 2

$ ~/Workspace/lpython/src/bin/lpython /var/tmp/lp/qux.py
semantic error: Arguments do not match for any generic procedure, _mod
 --> /var/tmp/lp/qux.py:4:19
  |
4 | bar: Const[i32] = foo % 2
  |                   ^^^^^^^


Note: Please report unclear or confusing messages as bugs at
https://github.com/lcompilers/lpython/issues.

[Thirumalai-Shaktivel]

I think, the Const[i32] is not handled in _lpython_floordiv and _mod

[abhi-glitchhg]

Can I try this one? Though I would need some guidance for this.

…

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[Thirumalai-Shaktivel]

Sure, go ahead and submit a PR!

[AnandRaj-7]

If i am right then this is becasue in C and C++ comments start with "//" so it is unable to recognize it as a floor division operator and thinks of it as a comment.

[certik]

No, the error comes from LPython not being able to find an implementation for this case. Rather, we should be routing this operation via an explicit ASR node, or via the IntrinsicFunction node.

[ubaidsk]

I think we can implement floordiv operation similar to the mod operation using IntrinsicFunction node as in lfortran/lfortran#2519.

[abhi-glitchhg]

I was thinking of overloading the _lpython_floordiv function with inputs dtypes const[i32]. is this approach not good/preferred?

[certik]

You can try it, and if the patch is simple, we can merge it as a short-term workaround. Floor belongs into ASR itself as IntrinsicFunction, so it's always better to invest into the long-term solution.

[certik]

The following now works:

$ cat qux.py 
from lpython import Const, i32
foo: Const[i32] = 4
bar: Const[i32] = foo // 2
print(foo, bar)
$ lpython qux.py
4 2

Thanks @Shaikh-Ubaid !