Call `basic_free_stack` before return statement

[Thirumalai-Shaktivel]

from lpython import S
from sympy import pi

def func() -> S:
    print(pi)
    return pi

def test_func():
    print(func())

test_func()

(SubroutineCall
    2 basic_const_pi
    2 basic_const_pi
    [((Var 3 _lpython_return_variable))]
    ()
)
(Return)
(SubroutineCall                    ;; <== Here
    2 basic_free_stack
    2 basic_free_stack
    [((Var 3 _lpython_return_variable))]
    ()
)
(SubroutineCall
    2 basic_free_stack
    2 basic_free_stack
    [((Var 3 stack0))]
    ()
)

[certik]

Consider this example:

from lpython import S
from sympy import pi, Symbol

def func() -> S:
    return pi

def test_func():
    z: S = func()
    print(z)

test_func()

I recommend to fix it by calling the subroutine_from_function pass, which transforms the above into the following ASR code:

from lpython import S
from sympy import pi, Symbol

def func(r: Out[S]) -> None:
    r = pi

def test_func():
    z: S
    func(z)
    print(z)

test_func()

And this code in turn should already work today, so nothing needs to be implemented in the Symbolic pass.

[certik]

The first issue to fix is:

$ lpython a.py --verbose
ASR Pass starts: 'nested_vars'
ASR Pass ends: 'nested_vars'
ASR Pass starts: 'global_stmts'
ASR Pass ends: 'global_stmts'
ASR Pass starts: 'init_expr'
ASR Pass ends: 'init_expr'
ASR Pass starts: 'implied_do_loops'
ASR Pass ends: 'implied_do_loops'
ASR Pass starts: 'class_constructor'
ASR Pass ends: 'class_constructor'
ASR Pass starts: 'pass_list_expr'
ASR Pass ends: 'pass_list_expr'
ASR Pass starts: 'where'
ASR Pass ends: 'where'
ASR Pass starts: 'subroutine_from_function'
ASR Pass ends: 'subroutine_from_function'
ASR Pass starts: 'array_op'
ASR Pass ends: 'array_op'
ASR Pass starts: 'symbolic'
Traceback (most recent call last):
  File "/Users/ondrej/repos/lpython/src/bin/lpython.cpp", line 1869
    err = compile_python_to_object_file(arg_file, tmp_o, runtime_library_dir,
  File "/Users/ondrej/repos/lpython/src/bin/lpython.cpp", line 828
    res = fe.get_llvm3(*asr, pass_manager, diagnostics, infile);
  File "/Users/ondrej/repos/lpython/src/lpython/python_evaluator.cpp", line 71
    run_fn, infile);
  File "/Users/ondrej/repos/lpython/src/libasr/codegen/asr_to_llvm.cpp", line 8925
    pass_manager.apply_passes(al, &asr, pass_options, diagnostics);
  File "/Users/ondrej/repos/lpython/src/libasr/pass/pass_manager.h", line 305
    apply_passes(al, asr, _passes, pass_options, diagnostics);
  File "/Users/ondrej/repos/lpython/src/libasr/pass/pass_manager.h", line 166
    if (!asr_verify(*asr, true, diagnostics)) {
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 1161
    v.visit_TranslationUnit(unit);
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 109
    for (auto &a : x.m_symtab->get_scope()) {
  File "../libasr/asr.h", line 5040
  File "../libasr/asr.h", line 4755
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 317
    for (auto &a : x.m_symtab->get_scope()) {
  File "../libasr/asr.h", line 5040
  File "../libasr/asr.h", line 4756
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 435
    visit_stmt(*x.m_body[i]);
  File "../libasr/asr.h", line 5057
  File "../libasr/asr.h", line 4806
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 870
    require(symtab_in_scope(current_symtab, x.m_name),
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 68
    unsigned int symtab_ID = symbol_parent_symtab(sym)->counter;
  File "/Users/ondrej/repos/lpython/src/libasr/asr_verify.cpp", line 68
    unsigned int symtab_ID = symbol_parent_symtab(sym)->counter;
  Binary file "/usr/lib/system/libsystem_platform.dylib", local address: 0x1803244e3
Segfault: Signal SIGSEGV (segmentation fault) received

[certik]

There are several independent issues that we need to fix:

• Call basic_free_stack before return statement #2411 (comment)
• Port the --dump-all-passes and --dump-all-passes-fortran from LFortran #2413
• Make sure the subroutine_from_function pass works as above
• Implemented visit_Return for freeing variables #2412 (not clear if it is related to this problem at all, but it's independent of the above two points)

[anutosh491]

Considering the above comment. I would say this

from lpython import S
from sympy import pi, Symbol

def func(r: Out[S]) -> None:
    r = pi

def test_func():
    z: S
    func(z)
    print(z)

test_func()

Should transform into something like this

def func(r: Out[CPtr]) -> None:
    basic_const_pi(r)

def test_func():
    _z: i64 = i64(0)
    z: CPtr = empty_c_void_p()
    p_c_pointer(pointer(_z, i64), z)
    basic_new_stack(z)
    func(z)
    print(basic_str(z))

test_func()

This works with the c backend

(lf) anutosh491@spbhat68:~/lpython/lpython$ lpython --enable-symengine --backend=c integration_tests/symbolics_08.py
pi

But with the llvm backend we face this issue

code generation error: asr_to_llvm: module failed verification. Error:
Call parameter type does not match function signature!
void** %r
 void*  call void @basic_const_pi(void** %r)
Call parameter type does not match function signature!
  %2 = load void*, void** %z, align 8
 void**  call void @__module___main___func(void* %2)

We define basic_const_pi like

@ccall(header="symengine/cwrapper.h", c_shared_lib="symengine", c_shared_lib_path=f"{os.environ['CONDA_PREFIX']}/lib")
def basic_const_pi(x: CPtr) -> None:
   pass

But if you see the error message it is passing a double pointer as the first argument. Is this because r has an intent of type Out ?
cc @certik @Thirumalai-Shaktivel

[Thirumalai-Shaktivel]

Yup, it's because of intent Out.
I don't know how to proceed here; I will have to look into it soon and report back.

[certik]

@anutosh491 yes, correct. I reopened this issue since the comment #2411 (comment) is not fixed. You are on the right track, we first need to get the Out[S] arguments working.

[anutosh491]

I think we have all 4 TODOS of #2411 (comment) addressed now. Hence the issue can be closed.

[certik]

@anutosh491 great job!