Handle array as return variable using the lpython decorator

[Thirumalai-Shaktivel]

Related to #703

[Thirumalai-Shaktivel]

Sometimes I get:

python(12438,0x1e33a1e00) malloc: Heap corruption detected, free list is damaged at 0x600000e7cb00
*** Incorrect guard value: 4634274385308418048
python(12438,0x1e33a1e00) malloc: *** set a breakpoint in malloc_error_break to debug

we need to fix this!

[Thirumalai-Shaktivel]

Here is the generated C code for the above function:

void multiply(int32_t n, struct r64* x, struct r64* _lpython_return_variable)
{
    int32_t __1_t;
    int32_t __1_v;
    int32_t i;
    for (i=0; i<=n - 1; i++) {
        x->data[(i - x->dims[0].lower_bound)] = x->data[(i - x->dims[0].lower_bound)]*  5.00000000000000000e+00;
    }
    __1_v = ((int32_t)x->dims[1-1].lower_bound);
    for (__1_t=((int32_t)_lpython_return_variable->dims[1-1].lower_bound); __1_t<=((int32_t) _lpython_return_variable->dims[1-1].length + _lpython_return_variable->dims[1-1].lower_bound - 1); __1_t++) {
        _lpython_return_variable->data[(__1_t - _lpython_return_variable->dims[0].lower_bound)] = x->data[(__1_v - x->dims[0].lower_bound)];
        __1_v = __1_v + 1;
    }
    return;
}

Here, I think the second for loop iteration should access the x variable instead of _lpython_return_variable. I need to investigate more about this.

[certik]

The second loop seems to copy x into _lpython_return_variable, which seems correct:

        _lpython_return_variable->data[(__1_t - _lpython_return_variable->dims[0].lower_bound)] = x->data[(__1_v - x->dims[0].lower_bound)];

[certik]

This needs to be changed to:

n = TypeVar("n")
def multiply(n: i32, x: f64[:]) -> f64[n]:

The return array must have a length that is determined using the function arguments.

[Thirumalai-Shaktivel]

Cool, @certik This PR is ready, kindly review and provide feedback, if any.

[Thirumalai-Shaktivel]

This: #1891 (comment) is fixed!

[certik]

I think this looks good.