Added support for functions to accept symbolic variables

[anutosh491]

Now that we have started porting sympy functions to LPython, I realized that there are some errors while trying to have symbolic parameters. Consider the following program

from sympy import pi, Symbol

def printsym(x: S):
    print(x)

def main0():
    a : S = Symbol("x")
    printsym(a)

If we look at the C code generated for this.

void printsym(void* x)
{
    _x = 0;
    x = NULL;
    x = (void*) &_x;
    basic_new_stack(x);
    printf("%s\n", basic_str(x));
    basic_free_stack(x);
}

void main0()
{
    int64_t _a;
    void* a;
    _a = 0;
    a = NULL;
    a = (void*) &_a;
    basic_new_stack(a);
    symbol_set(a, "x");
    printsym(a);
    basic_free_stack(a);
}

But this would end up giving a segmentation fault, we don't need to apply the transformations which we apply on local variables (a in this case) to the parameterized variable (x in this case). Something as simple as the following would do the job.

void printsym(void* x)
{
    printf("%s\n", basic_str(x));
}

Hence the changes introduced are the following

1. Only apply the transformation if a local variable is being considered. Taken care through an if check
2. The parameter x: S is being changed to x: CPtr to replicate the void pointer (printsym(void* x))
3. I don't think the parameterized variables need to be freed, only the local ones should be hence that is being taken care of .For eg

def printsym(x: S):
   a: S = pi
   print(a)
   print(x)

Here a should be freed but freeing of x has been taken care in main0

[anutosh491]

An example for reference

(lf) anutosh491@spbhat68:~/lpython/lpython$ cat examples/expr2.py 
from sympy import pi, Symbol

def printsym(x: S, y: S):
    z: S = Symbol("z")
    print(x + y + z + pi)

def main0():
    a : S = Symbol("x")
    b : S = Symbol("y")
    printsym(a, b)

if __name__ == "__main__":
   main0()
(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --enable-symengine --backend=llvm  examples/expr2.py 
x + y + z + pi
(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --enable-symengine --backend=c  examples/expr2.py 
x + y + z + pi

[certik]

Can you add a test for this?

[anutosh491]

I think so maybe we would need a visit_SubRoutineCall function in our pass to handle something like this

from sympy import pi, Symbol
from lpython import S

def printsym(x: S):
    print(x)

def main0():
    printsym(Symbol("x"))

main0()

Where we are passing Symbol("x") directly rather than storing it in a symbolic variable first and then moving on from there.
I'll try to get this soon and add tests for the same .

[certik]

Just add a test for the feature you implemented in this PR, and later once you implement printsym(Symbol("x")) you can test it too.

[anutosh491]

Yes, I think so I can implement the case for printsym(Symbol("x")) ( through a visit_SubroutineCall function) in the subsequent PR.

[anutosh491]

Also I am not sure why do we get an error through the llvm backend. Everything looks correct to me as in I don't see any obvious error . Consider this simple program

from sympy import pi, Symbol

def main0():
    i: i32 = 2
    _i: S = S(i)
    print(_i)

The C backend works perfectly

(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --show-c examples/expr2.py 

void main0()
{
    int64_t __i;
    void* _i;
    int32_t i;
    __i = 0;
    _i = NULL;
    _i = (void*) &__i;
    basic_new_stack(_i);
    i = 2;
    integer_set_si(_i, i);
    printf("%s\n", basic_str(_i));
    basic_free_stack(_i);
}

(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --enable-symengine --backend=c examples/expr2.py 
2
(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --show-llvm examples/expr2.py 

declare void @_lpython_set_argv(i32, i8**)
code generation error: asr_to_llvm: module failed verification. Error:
Call parameter type does not match function signature!
  %3 = load i32, i32* %i, align 4
 i64  call void @integer_set_si(void* %2, i32 %3)

@Thirumalai-Shaktivel would you mind helping me out here. Once this is fixed the failing llvm_sym test woudl work as expected.

[Thirumalai-Shaktivel]

I think you have to cast the second argument from i32 to i64. As you can see, declare accepts i64.

declare void @integer_set_si(void*, i64)
...
  %3 = load i32, i32* %i, align 4
  call void @integer_set_si(void* %2, i32 %3)
...

In C, I think there might be an implicit cast for i32 to i64, so it works.

[anutosh491]

I think you have to cast the second argument from i32 to i64. As you can see, declare accepts i64.

Oops, sorry I think so I overlooked this. Thanks for the help !
This is now ready.

[anutosh491]

I have a few doubts regarding few corner cases, hence converting to draft.

[anutosh491]

I think this is ready now.

[certik]

I think that this is good. Thanks!