python confusing behavior due to implicit casting

[111116]

import luisa
luisa.init('cuda')

@luisa.func
def f():
    if dispatch_id().x == 999:
        a = 0
    else:
        a = 0.5
    print('a:', a)

f(dispatch_size=1)

Result:

a: 0

While the expected result is 0.5.

---

Change the condition to False and result will become a: 0.5

---

Above code crashes when using cpu backend instead:

thread '<unnamed>' panicked at 'index out of bounds: the len is 5 but the index is 5', luisa_compute_backend_impl/src/cpu/codegen/cpp.rs:1799:16
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
terminate called without an active exception

[Mike-Leo-Smith]

The type of a variable is decided at its first occurrence so

if dispatch_id().x == 999:
        a = 0
    else:
        a = 0.5

leads to an int-typed a (as initialized by int(0)).

On the other hand, we perform some basic control flow simplification, so if you change the condition to a constant False, the above code folds to the unbranched version

    a = 0.5

where a now is initialized by a float(0.5).

You may solve such inconsistence by either changing 0 to 0.0 or explicitly type a as float aforehand:

import luisa
luisa.init('cuda')

@luisa.func
def f():
    a = float()
    if dispatch_id().x == 999:
        a = 0
    else:
        a = 0.5
    print('a:', a)

f(dispatch_size=1)

[Mike-Leo-Smith]

Above code crashes when using cpu backend instead:

thread '<unnamed>' panicked at 'index out of bounds: the len is 5 but the index is 5', luisa_compute_backend_impl/src/cpu/codegen/cpp.rs:1799:16
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
terminate called without an active exception

This should have been fixed in new luisa-python releases. Please upgrade with the following command:

python -m pip install -U luisa-python