Re: [PATCH 6/8] coroutines: Convert implementation variables to debug-friendly form.

[Jason Merrill <jason@redhat.com>]

On 9/1/21 6:55 AM, Iain Sandoe wrote:
> 
> The user might well wish to inspect some of the state that represents
> the implementation of the coroutine machine.
> 
> In particular:
>    The promise object.
>    The function pointers for the resumer and destroyer.
>    The current resume index (suspend point).
>    The handle that represent this coroutine 'self handle'.
>    Whether the coroutine frame is allocated and needs to be freed.
> 
> These variables are given names that can be 'well-known' and advertised
> in debug documentation - they are placed in the implementation namespace
> and all begin with _Coro_.

> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> gcc/cp/ChangeLog:
> 
> 	* coroutines.cc (transform_await_expr): Use debug-friendly
> 	names for coroutine implementation.
> 	(build_actor_fn): Likewise.
> 	(build_destroy_fn): Likewise.
> 	(coro_rewrite_function_body): Likewise.
> 	(morph_fn_to_coro): Likewise.

Hmm, this patch doesn't seem to match the description and ChangeLog 
entry other than in the names of the functions changed.

> ---
>   gcc/cp/coroutines.cc | 214 +++++++++++++++++++------------------------
>   1 file changed, 94 insertions(+), 120 deletions(-)
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index 3b46aac4dc5..aacf352f1c9 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -1906,7 +1906,6 @@ transform_await_expr (tree await_expr, await_xform_data *xform)
>     /* So, on entry, we have:
>        in : CO_AWAIT_EXPR (a, e_proxy, o, awr_call_vector, mode)
>   	  We no longer need a [it had diagnostic value, maybe?]
> -	  We need to replace the promise proxy in all elements
>   	  We need to replace the e_proxy in the awr_call.  */
>   
>     tree coro_frame_type = TREE_TYPE (xform->actor_frame);
> @@ -1932,16 +1931,6 @@ transform_await_expr (tree await_expr, await_xform_data *xform)
>         TREE_OPERAND (await_expr, 1) = as;
>       }
>   
> -  /* Now do the self_handle.  */
> -  data.from = xform->self_h_proxy;
> -  data.to = xform->real_self_h;
> -  cp_walk_tree (&await_expr, replace_proxy, &data, NULL);
> -
> -  /* Now do the promise.  */
> -  data.from = xform->promise_proxy;
> -  data.to = xform->real_promise;
> -  cp_walk_tree (&await_expr, replace_proxy, &data, NULL);
> -
>     return await_expr;
>   }
>   
> @@ -2128,10 +2117,9 @@ coro_get_frame_dtor (tree coro_fp, tree orig, tree frame_size,
>   
>   static void
>   build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
> -		tree orig, hash_map<tree, param_info> *param_uses,
> -		hash_map<tree, local_var_info> *local_var_uses,
> -		vec<tree, va_gc> *param_dtor_list, tree resume_fn_field,
> -		tree resume_idx_field, unsigned body_count, tree frame_size)
> +		tree orig, hash_map<tree, local_var_info> *local_var_uses,
> +		vec<tree, va_gc> *param_dtor_list,
> +		tree resume_idx_var, unsigned body_count, tree frame_size)
>   {
>     verify_stmt_tree (fnbody);
>     /* Some things we inherit from the original function.  */
> @@ -2216,8 +2204,8 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>       = {actor, actor_frame, coro_frame_type, loc, local_var_uses};
>     cp_walk_tree (&fnbody, transform_local_var_uses, &xform_vars_data, NULL);
>   
> -  tree rat_field = lookup_member (coro_frame_type, coro_resume_index_field, 1, 0,
> -				  tf_warning_or_error);
> +  tree rat_field = lookup_member (coro_frame_type, coro_resume_index_field,
> +				  1, 0, tf_warning_or_error);
>     tree rat = build3 (COMPONENT_REF, short_unsigned_type_node, actor_frame,
>   		     rat_field, NULL_TREE);
>   
> @@ -2319,14 +2307,8 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>     tree r = build_stmt (loc, LABEL_EXPR, actor_begin_label);
>     add_stmt (r);
>   
> -  /* actor's version of the promise.  */
> -  tree ap_m = lookup_member (coro_frame_type, get_identifier ("_Coro_promise"), 1, 0,
> -			     tf_warning_or_error);
> -  tree ap = build_class_member_access_expr (actor_frame, ap_m, NULL_TREE, false,
> -					    tf_warning_or_error);
> -
>     /* actor's coroutine 'self handle'.  */
> -  tree ash_m = lookup_member (coro_frame_type, get_identifier ("_Coro_self_handle"), 1,
> +  tree ash_m = lookup_member (coro_frame_type, coro_self_handle_field, 1,
>   			      0, tf_warning_or_error);
>     tree ash = build_class_member_access_expr (actor_frame, ash_m, NULL_TREE,
>   					     false, tf_warning_or_error);
> @@ -2347,36 +2329,13 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>        decide where to put things.  */
>   
>     await_xform_data xform
> -    = {actor, actor_frame, promise_proxy, ap, self_h_proxy, ash};
> +    = {actor, actor_frame, NULL_TREE, NULL_TREE, self_h_proxy, ash};
>   
>     /* Transform the await expressions in the function body.  Only do each
>        await tree once!  */
>     hash_set<tree> pset;
>     cp_walk_tree (&fnbody, transform_await_wrapper, &xform, &pset);
>   
> -  /* Now replace the promise proxy with its real value.  */
> -  proxy_replace p_data;
> -  p_data.from = promise_proxy;
> -  p_data.to = ap;
> -  cp_walk_tree (&fnbody, replace_proxy, &p_data, NULL);
> -
> -  /* The rewrite of the function adds code to set the resume_fn field to
> -     nullptr when the coroutine is done and also the index to zero when
> -     calling an unhandled exception.  These are represented by two proxies
> -     in the function, so rewrite them to the proper frame access.  */
> -  tree resume_m
> -    = lookup_member (coro_frame_type, get_identifier ("_Coro_resume_fn"),
> -		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
> -  tree res_x = build_class_member_access_expr (actor_frame, resume_m, NULL_TREE,
> -					       false, tf_warning_or_error);
> -  p_data.from = resume_fn_field;
> -  p_data.to = res_x;
> -  cp_walk_tree (&fnbody, replace_proxy, &p_data, NULL);
> -
> -  p_data.from = resume_idx_field;
> -  p_data.to = rat;
> -  cp_walk_tree (&fnbody, replace_proxy, &p_data, NULL);
> -
>     /* Add in our function body with the co_returns rewritten to final form.  */
>     add_stmt (fnbody);
>   
> @@ -2385,7 +2344,7 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>     add_stmt (r);
>   
>     /* Destructors for the things we built explicitly.  */
> -  r = build_special_member_call (ap, complete_dtor_identifier, NULL,
> +  r = build_special_member_call (promise_proxy, complete_dtor_identifier, NULL,
>   				 promise_type, LOOKUP_NORMAL,
>   				 tf_warning_or_error);
>     add_stmt (r);
> @@ -2398,7 +2357,7 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>     /* Here deallocate the frame (if we allocated it), which we will have at
>        present.  */
>     tree fnf_m
> -    = lookup_member (coro_frame_type, get_identifier ("_Coro_frame_needs_free"), 1,
> +    = lookup_member (coro_frame_type, coro_frame_needs_free_field, 1,
>   		     0, tf_warning_or_error);
>     tree fnf2_x = build_class_member_access_expr (actor_frame, fnf_m, NULL_TREE,
>   						false, tf_warning_or_error);
> @@ -2477,18 +2436,10 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>     gcc_checking_assert (maybe_cleanup_point_expr_void (r) == r);
>     add_stmt (r);
>   
> -  /* We will need to know which resume point number should be encoded.  */
> -  tree res_idx_m
> -    = lookup_member (coro_frame_type, coro_resume_index_field,
> -		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
> -  tree resume_pt_number
> -    = build_class_member_access_expr (actor_frame, res_idx_m, NULL_TREE, false,
> -				      tf_warning_or_error);
> -
>     /* We've now rewritten the tree and added the initial and final
>        co_awaits.  Now pass over the tree and expand the co_awaits.  */
>   
> -  coro_aw_data data = {actor, actor_fp, resume_pt_number, NULL_TREE,
> +  coro_aw_data data = {actor, actor_fp, resume_idx_var, NULL_TREE,
>   		       ash, del_promise_label, ret_label,
>   		       continue_label, continuation, 2};
>     cp_walk_tree (&actor_body, await_statement_expander, &data, NULL);
> @@ -2502,7 +2453,7 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
>   }
>   
>   /* The prototype 'destroy' function :
> -   frame->__resume_at |= 1;
> +   frame->__Coro_resume_index |= 1;
>      actor (frame);  */
>   
>   static void
> @@ -2521,10 +2472,10 @@ build_destroy_fn (location_t loc, tree coro_frame_type, tree destroy,
>   
>     tree destr_frame = build1 (INDIRECT_REF, coro_frame_type, destr_fp);
>   
> -  tree rat_field = lookup_member (coro_frame_type, coro_resume_index_field, 1, 0,
> -				  tf_warning_or_error);
> -  tree rat = build3 (COMPONENT_REF, short_unsigned_type_node, destr_frame,
> -		     rat_field, NULL_TREE);
> +  tree rat_field = lookup_member (coro_frame_type, coro_resume_index_field,
> +				  1, 0, tf_warning_or_error);
> +  tree rat = build3 (COMPONENT_REF, short_unsigned_type_node,
> +			 destr_frame, rat_field, NULL_TREE);
>   
>     /* _resume_at |= 1 */
>     tree dstr_idx = build2 (BIT_IOR_EXPR, short_unsigned_type_node, rat,
> @@ -4040,8 +3991,8 @@ coro_build_actor_or_destroy_function (tree orig, tree fn_type,
>   
>   static tree
>   coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
> -			    tree resume_fn_ptr_type, tree& resume_fn_field,
> -			    tree& resume_idx_field, tree& fs_label)
> +			    tree resume_fn_ptr_type,
> +			    tree& resume_idx_var, tree& fs_label)
>   {
>     /* This will be our new outer scope.  */
>     tree update_body = build3 (BIND_EXPR, void_type_node, NULL, NULL, NULL);
> @@ -4074,7 +4025,6 @@ coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
>   
>     /* Wrap the function body in a try {} catch (...) {} block, if exceptions
>        are enabled.  */
> -  tree promise = get_coroutine_promise_proxy (orig);
>     tree var_list = NULL_TREE;
>     tree initial_await = build_init_or_final_await (fn_start, false);
>   
> @@ -4085,24 +4035,61 @@ coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
>     tree return_void
>       = get_coroutine_return_void_expr (current_function_decl, fn_start, false);
>   
> +  /* The pointer to the resume function.  */
> +  tree resume_fn_ptr
> +    = coro_build_artificial_var (fn_start, coro_resume_fn_field,
> +				 resume_fn_ptr_type, orig, NULL_TREE);
> +  DECL_CHAIN (resume_fn_ptr) = var_list;
> +  var_list = resume_fn_ptr;
> +  add_decl_expr (resume_fn_ptr);
> +
>     /* We will need to be able to set the resume function pointer to nullptr
>        to signal that the coroutine is 'done'.  */
> -  resume_fn_field
> -    = build_lang_decl (VAR_DECL, get_identifier ("resume.fn.ptr.proxy"),
> -		       resume_fn_ptr_type);
> -  DECL_ARTIFICIAL (resume_fn_field) = true;
>     tree zero_resume
>       = build1 (CONVERT_EXPR, resume_fn_ptr_type, integer_zero_node);
> -  zero_resume
> -    = build2 (INIT_EXPR, resume_fn_ptr_type, resume_fn_field, zero_resume);
> -  /* Likewise, the resume index needs to be reset.  */
> -  resume_idx_field
> -    = build_lang_decl (VAR_DECL, get_identifier ("resume.index.proxy"),
> -		       short_unsigned_type_node);
> -  DECL_ARTIFICIAL (resume_idx_field) = true;
> -  tree zero_resume_idx = build_int_cst (short_unsigned_type_node, 0);
> -  zero_resume_idx = build2 (INIT_EXPR, short_unsigned_type_node,
> -			    resume_idx_field, zero_resume_idx);
> +
> +  /* The pointer to the destroy function.  */
> +  tree var = coro_build_artificial_var (fn_start, coro_destroy_fn_field,
> +					resume_fn_ptr_type, orig, NULL_TREE);
> +  DECL_CHAIN (var) = var_list;
> +  var_list = var;
> +  add_decl_expr (var);
> +
> +  /* The promise was created on demand when parsing we now link it into
> +      our scope.  */
> +  tree promise = get_coroutine_promise_proxy (orig);
> +  DECL_CONTEXT (promise) = orig;
> +  DECL_SOURCE_LOCATION (promise) = fn_start;
> +  DECL_CHAIN (promise) = var_list;
> +  var_list = promise;
> +  add_decl_expr (promise);
> +
> +  /* We need a handle to this coroutine, which is passed to every
> +     await_suspend().  This was created on demand when parsing we now link it
> +     into our scope.  */
> +  var = get_coroutine_self_handle_proxy (orig);
> +  DECL_CONTEXT (var) = orig;
> +  DECL_SOURCE_LOCATION (var) = fn_start;
> +  DECL_CHAIN (var) = var_list;
> +  var_list = var;
> +  add_decl_expr (var);
> +
> +
> +  /* We create a resume index, this is initialized in the ramp.  */
> +  resume_idx_var
> +    = coro_build_artificial_var (fn_start, coro_resume_index_field,
> +				 short_unsigned_type_node, orig, NULL_TREE);
> +  DECL_CHAIN (resume_idx_var) = var_list;
> +  var_list = resume_idx_var;
> +  add_decl_expr (resume_idx_var);
> +
> +  /* If the coroutine has a frame that needs to be freed, this will be set by
> +     the ramp.  */
> +  var = coro_build_artificial_var (fn_start, coro_frame_needs_free_field,
> +				   boolean_type_node, orig, NULL_TREE);
> +  DECL_CHAIN (var) = var_list;
> +  var_list = var;
> +  add_decl_expr (var);
>   
>     if (flag_exceptions)
>       {
> @@ -4166,10 +4153,14 @@ coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
>   	 If the unhandled exception method returns, then we continue
>   	 to the final await expression (which duplicates the clearing of
>   	 the field). */
> -      finish_expr_stmt (zero_resume);
> -      finish_expr_stmt (zero_resume_idx);
> -      ueh = maybe_cleanup_point_expr_void (ueh);
> -      add_stmt (ueh);
> +      tree r = build2 (MODIFY_EXPR, resume_fn_ptr_type, resume_fn_ptr,
> +		       zero_resume);
> +      finish_expr_stmt (r);
> +      tree short_zero = build_int_cst (short_unsigned_type_node, 0);
> +      r = build2 (MODIFY_EXPR, short_unsigned_type_node, resume_idx_var,
> +		  short_zero);
> +      finish_expr_stmt (r);
> +      finish_expr_stmt (ueh);
>         finish_handler (handler);
>         TRY_HANDLERS (tcb) = pop_stmt_list (TRY_HANDLERS (tcb));
>       }
> @@ -4204,6 +4195,8 @@ coro_rewrite_function_body (location_t fn_start, tree fnbody, tree orig,
>     /* Before entering the final suspend point, we signal that this point has
>        been reached by setting the resume function pointer to zero (this is
>        what the 'done()' builtin tests) as per the current ABI.  */
> +  zero_resume = build2 (MODIFY_EXPR, resume_fn_ptr_type, resume_fn_ptr,
> +			zero_resume);
>     finish_expr_stmt (zero_resume);
>     finish_expr_stmt (build_init_or_final_await (fn_start, true));
>     BIND_EXPR_BODY (update_body) = pop_stmt_list (BIND_EXPR_BODY (update_body));
> @@ -4348,33 +4341,16 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>     /* Construct the wrapped function body; we will analyze this to determine
>        the requirements for the coroutine frame.  */
>   
> -  tree resume_fn_field = NULL_TREE;
> -  tree resume_idx_field = NULL_TREE;
> +  tree resume_idx_var = NULL_TREE;
>     tree fs_label = NULL_TREE;
>     fnbody = coro_rewrite_function_body (fn_start, fnbody, orig,
> -				       act_des_fn_ptr, resume_fn_field,
> -				       resume_idx_field, fs_label);
> +				       act_des_fn_ptr,
> +				       resume_idx_var, fs_label);
>     /* Build our dummy coro frame layout.  */
>     coro_frame_type = begin_class_definition (coro_frame_type);
>   
> +  /* The fields for the coro frame.  */
>     tree field_list = NULL_TREE;
> -  tree resume_name
> -    = coro_make_frame_entry (&field_list, "_Coro_resume_fn",
> -			     act_des_fn_ptr, fn_start);
> -  tree destroy_name
> -    = coro_make_frame_entry (&field_list, "_Coro_destroy_fn",
> -			     act_des_fn_ptr, fn_start);
> -  tree promise_name
> -    = coro_make_frame_entry (&field_list, "_Coro_promise", promise_type, fn_start);
> -  tree fnf_name = coro_make_frame_entry (&field_list, "_Coro_frame_needs_free",
> -					 boolean_type_node, fn_start);
> -  tree resume_idx_name
> -    = coro_make_frame_entry (&field_list, "_Coro_resume_index",
> -			     short_unsigned_type_node, fn_start);
> -
> -  /* We need a handle to this coroutine, which is passed to every
> -     await_suspend().  There's no point in creating it over and over.  */
> -  (void) coro_make_frame_entry (&field_list, "_Coro_self_handle", handle_type, fn_start);
>   
>     /* Now add in fields for function params (if there are any).
>        We do not attempt elision of copies at this stage, we do analyze the
> @@ -4776,8 +4752,8 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   
>     /* For now, once allocation has succeeded we always assume that this needs
>        destruction, there's no impl. for frame allocation elision.  */
> -  tree fnf_m
> -    = lookup_member (coro_frame_type, fnf_name, 1, 0, tf_warning_or_error);
> +  tree fnf_m = lookup_member (coro_frame_type, coro_frame_needs_free_field,
> +			      1, 0,tf_warning_or_error);
>     tree fnf_x = build_class_member_access_expr (deref_fp, fnf_m, NULL_TREE,
>   					       false, tf_warning_or_error);
>     r = build2 (INIT_EXPR, boolean_type_node, fnf_x, boolean_true_node);
> @@ -4788,24 +4764,22 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   
>     tree actor_addr = build1 (ADDR_EXPR, act_des_fn_ptr, actor);
>     tree resume_m
> -    = lookup_member (coro_frame_type, resume_name,
> +    = lookup_member (coro_frame_type, coro_resume_fn_field,
>   		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
>     tree resume_x = build_class_member_access_expr (deref_fp, resume_m, NULL_TREE,
>   						  false, tf_warning_or_error);
>     r = build2_loc (fn_start, INIT_EXPR, act_des_fn_ptr, resume_x, actor_addr);
> -  r = coro_build_cvt_void_expr_stmt (r, fn_start);
> -  add_stmt (r);
> +  finish_expr_stmt (r);
>   
>     tree destroy_addr = build1 (ADDR_EXPR, act_des_fn_ptr, destroy);
>     tree destroy_m
> -    = lookup_member (coro_frame_type, destroy_name,
> +    = lookup_member (coro_frame_type, coro_destroy_fn_field,
>   		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
>     tree destroy_x
>       = build_class_member_access_expr (deref_fp, destroy_m, NULL_TREE, false,
>   				      tf_warning_or_error);
>     r = build2_loc (fn_start, INIT_EXPR, act_des_fn_ptr, destroy_x, destroy_addr);
> -  r = coro_build_cvt_void_expr_stmt (r, fn_start);
> -  add_stmt (r);
> +  finish_expr_stmt (r);
>   
>     /* [dcl.fct.def.coroutine] /13
>        When a coroutine is invoked, a copy is created for each coroutine
> @@ -4896,7 +4870,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   
>     /* Set up the promise.  */
>     tree promise_m
> -    = lookup_member (coro_frame_type, promise_name,
> +    = lookup_member (coro_frame_type, coro_promise_field,
>   		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
>   
>     tree p = build_class_member_access_expr (deref_fp, promise_m, NULL_TREE,
> @@ -5042,9 +5016,9 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   			      boolean_type_node);
>         finish_expr_stmt (r);
>       }
> -  /* Initialize the resume_idx_name to 0, meaning "not started".  */
> +  /* Initialize the resume_idx_var to 0, meaning "not started".  */
>     tree resume_idx_m
> -    = lookup_member (coro_frame_type, resume_idx_name,
> +    = lookup_member (coro_frame_type, coro_resume_index_field,
>   		     /*protect=*/1, /*want_type=*/0, tf_warning_or_error);
>     tree resume_idx
>       = build_class_member_access_expr (deref_fp, resume_idx_m, NULL_TREE, false,
> @@ -5187,9 +5161,9 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>     push_deferring_access_checks (dk_no_check);
>   
>     /* Build the actor...  */
> -  build_actor_fn (fn_start, coro_frame_type, actor, fnbody, orig, param_uses,
> -		  &local_var_uses, param_dtor_list, resume_fn_field,
> -		  resume_idx_field, body_aw_points.await_number, frame_size);
> +  build_actor_fn (fn_start, coro_frame_type, actor, fnbody, orig,
> +		  &local_var_uses, param_dtor_list,
> +		  resume_idx_var, body_aw_points.await_number, frame_size);
>   
>     /* Destroyer ... */
>     build_destroy_fn (fn_start, coro_frame_type, destroy, actor);
>