As we mentioned yesterday at #ps, we're going to have a hackathon on Saturday to get the args/returns refactor started. Information about the refactor is located on the wiki:
http://trac.parrot.org/parrot/wiki/CallingConventionsTasklist For people who aren't familiar with the task at hand, here's a nutshell version: In current function calls in PIR, we call the get_results opcode BEFORE we invoke the Sub PMC. This means two things: (1) we have to pack pointers to the return results into the CallContext PMC, and (2) we need to use different functions for passing arguments and passing returns, even though the two should use the same mechanism. After the refactor, both function call and function return will use the same mechanism: Pass "arguments" ("returns") into a CallContext, invoke the function (invoke the return), and unpack the "parameters" ("results"). To make this work, there are a few tasks to complete. I'm listing them in a general order that I think things could go in, but this isn't a firm timeline: 1) We need to modify IMCC to output the correct opcode sequence for a function call. I'm sure it's not so simple, but it looks to me like the primary place to make this change is going to be in compilers/imcc/pcc.c:expand_pcc_sub_call(), and related functions. 2) We need to remove return_flags, current_returns, returns_values, returns_sizes and returns_size_threshold attributes, and supporting code from CallContext PMC. 3) Modify the set_returns opcode to create a new CallContext to pass the returns. set_returns is going to act almost identically to the set_args opcode. We need to build the CallContext, passing the returns like how set_args passes arguments. The relevant ops are in src/ops/core.ops. We're probably also going to need to look at src/call/args.c:Parrot_pcc_build_sig_object_from_op(), mostly for inspiration. We should probably delete src/call/args.c:Parrot_pcc_build_sig_object_returns_from_op(), replacing with the former function. 4) We need to unify the argument passing code. Specifically, we need to unify the functions src/call/args.c:Parrot_pcc_fill_params_from_op with src/call/args.c:Parrot_pcc_fill_returns_from_op, and unify src/call/args.c:Parrot_pcc_fill_params_from_varargs with src/call/args.c:Parrot_pcc_fill_returns_from_varargs. We're also going to need to take a close look at src/call/args.c:Parrot_pcc_fill_returns_from_continuation. At the very least we should rename it to "Parrot_pcc_fill_params_from_continuation". 5) Unify supporting functions, src/call/args.c:fill_params with src/call/args.c:fill_results. These functions are large and ugly, so this could be the hardest part of the refactor. Also, merge src/call/args.c:assign_default_result_value -> src/call/args.c:assign_default_param_value. 6) Find and kill any dead code that is no longer used. I think that's a pretty comprehensive list of the tasks that need to be completed for this hackathon. I'm sure I'm missing something, so please post a follow-up email if you can point other items out. There is a branch for this already, but it's several days old. If there are no commits to the branch, we'll delete it and create a new more up-to-date branch on Friday to support the work. Comments/questions can come to the list or go to IRC if people are around. Send me a message and I'll make sure you get the answers you need, or I'll make sure to get you in touch with whoever has answers. Clarifications for various subtasks can go to the wiki. I look forward to seeing a bunch of hackers on Saturday! --Andrew Whitworth _______________________________________________ http://lists.parrot.org/mailman/listinfo/parrot-dev
