Full C calling convention

[raviqqe]

Problems

• High-level programming languages have FFI compatible with C calling convention and ABI.
• If F-- is used as backend, people need to implement those by themselves as the LLVM backend doesn't implement this properly.
  • struct type arguments are not put on stacks and passed as pointers.
  • Values of struct types are not returned from functions through mutable memory which is allocated on the caller side.
• In those high-level programming languages, it's also a solution to allocate heap always for struct types although that incurs extra overhead.

Solution

• Implement C calling convention for the target calling convention.
• It might make sense to add another c calling convention as the ABI requirements are only required in FFI.

References

• C wrapper emission | MLIR

[raviqqe]

Closed by #349.