Stream: general

Topic: Componnet model: canonical ABI for return values

Wang Xin (Aug 31 2023 at 23:37):

Hi @Luke Wagner I have a question regard to the return values in the cannon-lift. The proposal simply put a "i32" type as flat_results. I wonder if we should be more specific about it? Like it is value or pointer? I assume if the ft has single primitive type as return, it can be a value. for other situation, it is probabaly a pointer to flatten items.

MAX_FLAT_PARAMS = 16
MAX_FLAT_RESULTS = 1

def flatten_functype(ft, context):
  flat_params = flatten_types(ft.param_types())
  if len(flat_params) > MAX_FLAT_PARAMS:
    flat_params = ['i32']

  flat_results = flatten_types(ft.result_types())
  if len(flat_results) > MAX_FLAT_RESULTS:
    match context:
      case 'lift':
        flat_results = ['i32']
      case 'lower':
        flat_params += ['i32']
        flat_results = []

  return CoreFuncType(flat_params, flat_results)

Luke Wagner (Aug 31 2023 at 23:40):

@Wang Xin thanks for the question: in this case where we have more than MAX_FLAT_RESULTS (currently 1, due to lack of multi-return support in certain parts of the LLVM toolchain), the i32 is always a pointer to linear memory that will hold all the return values as a tuple. (Once multi-return support is implemented in the right places, we can increase MAX_FLAT_RESULTS or add a canonopt to do that.)

Wang Xin (Aug 31 2023 at 23:48):

@Luke Wagner Thanks! I got it.

Last updated: Nov 22 2024 at 17:03 UTC