Support passing dict as return value of functions

[harshsingh-24]

Adds to #983 by giving full support of dictionary return type in LLVM and C backend respectively.

[harshsingh-24]

Hey @certik @Thirumalai-Shaktivel . Can you please help me out a little with this implementation? I am facing issues. If you can point me out a little to some portions. After doing this, it basically says AssertFailed: src->getType() == dest->getType() when deep_copy method of dict is being called.

Test case -

def fun() -> dict[i32, i32]:
    return {2: 4, 3: 6}

num : dict[i32, i32]
num = fun()
print(num[2])

Also, I have witnessed that while deep copying - the value dict and target dict are as follows -

VALUE DICT
 %0 = call %dict @__module__global_symbols_fun()
TARGET DICT
@num = global %dict zeroinitializer

I feel that for it should be something of %0 = alloca % dict, align 8 or similar to that? What do you think?

[czgdp1807]

I tried your branch by commenting out the last two lines in your example,

from lpython import i32

def fun() -> dict[i32, i32]:
    return {2: 4, 3: 6}

num : dict[i32, i32]
# num = fun()
# print(num[2])

LLVM code,

; ModuleID = 'LFortran'
source_filename = "LFortran"

%dict = type { i32, %list, %list, i8* }
%list = type { i32, i32, i32* }

@num = global %dict zeroinitializer

define %dict @fun() {
.entry:
  %_lpython_return_variable = alloca %dict, align 8
  %const_dict = alloca %dict, align 8
  %0 = getelementptr %dict, %dict* %const_dict, i32 0, i32 0
  store i32 0, i32* %0, align 4
.
.
.

You can see fun is returning a dict (non-pointer) where as @num is a pointer that's why the assert fails. Now how do we fix this? In a way similar how we do it for lists (check integration_tests/test_list_01.py and see the LLVM code generated for that test, same pattern can be applied to dicts as well).

P.S. Also read #955 (comment)

[harshsingh-24]

@czgdp1807 I added ASR::is_a<ASR::Dict_t>(*asr_type) to the check static inline bool is_llvm_struct(ASR::ttype_t* asr_type) in llvm_utils.h to incorporate Dict return type using the above logic as suggested by you.

[harshsingh-24]

Can you please check @Thirumalai-Shaktivel and @czgdp1807 as to why the build is failing on C Backend?

[czgdp1807]

code generation error: Return type not supported in function 'fill_rollnumber2cpi'

You need to support dict as a return type in C backend as well (concerned files asr_to_c.cpp, asr_to_c_cpp.h and asr_to_cpp.h).

[harshsingh-24]

Can you please review ? @Thirumalai-Shaktivel @czgdp1807 @certik

[harshsingh-24]

Can you review? @czgdp1807 @certik . CI tests have passed.

[certik]

This looks good to me, but I would like @czgdp1807 to also review. The history needs polishing or squashing. I rebased on top of the latest master.