[PATCH] coroutines: Add a cleanup expression for g-r-o when needed [PR95477].

[Nathan Sidwell]

On 6/8/20 5:17 AM, Iain Sandoe wrote:
> Hi
> 
> The PR reports that we fail to destroy the object initially created from
> the get-return-object call.   Fixed by adding a cleanup when the DTOR is
> non-trivial.  In addition, to meet the specific wording that the call to
> get_return_object creates the glvalue for the return, we must construct
> that in-place in the return object to avoid a second copy/move CTOR.
> 
> tested on x86_64,powerpc64-linux, x86_64-darwin
> OK for master?
> 10.2?
> thanks
> Iain
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/95477
> 	* coroutines.cc (morph_fn_to_coro): Apply a cleanup to
> 	the get return object when the DTOR is non-trivial.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/coroutines/pr95477.C: New test.
> ---
>   gcc/cp/coroutines.cc                      | 61 +++++++++++++++++++----
>   gcc/testsuite/g++.dg/coroutines/pr95477.C | 37 ++++++++++++++
>   2 files changed, 89 insertions(+), 9 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/coroutines/pr95477.C
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index f2d7853477d..5a78bec1c9a 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -4284,12 +4284,34 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   
>     tree gro = NULL_TREE;
>     tree gro_bind_vars = NULL_TREE;
> +  tree gro_cleanup_stmt = NULL_TREE;
>     /* We have to sequence the call to get_return_object before initial
>        suspend.  */
>     if (gro_is_void_p)
> -    finish_expr_stmt (get_ro);
> +    r = get_ro;
> +  else if (same_type_p (gro_type, fn_return_type))
> +    {
> +     /* [dcl.fct.def.coroutine] / 7
> +	The expression promise.get_return_object() is used to initialize the
> +	glvalue result or... (see below)
> +	Construct the return result directly.  */
> +      if (TYPE_NEEDS_CONSTRUCTING (gro_type))
> +	{
> +	  vec<tree, va_gc> *arg = make_tree_vector_single (get_ro);
> +	  r = build_special_member_call (DECL_RESULT (orig),
> +					 complete_ctor_identifier,
> +					 &arg, gro_type, LOOKUP_NORMAL,
> +					 tf_warning_or_error);
> +	  release_tree_vector (arg);
> +	}
> +      else
> +	r = build2_loc (fn_start, INIT_EXPR, gro_type,
> +			DECL_RESULT (orig), get_ro);
> +    }
>     else
>       {
> +      /* ... or ... Construct an object that will be used as the single
> +	param to the CTOR for the return object.  */
>         gro = build_lang_decl (VAR_DECL, get_identifier ("coro.gro"), gro_type);
>         DECL_CONTEXT (gro) = current_scope ();
>         DECL_ARTIFICIAL (gro) = true;
> @@ -4306,8 +4328,21 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   	}
>         else
>   	r = build2_loc (fn_start, INIT_EXPR, gro_type, gro, get_ro);
> -      finish_expr_stmt (r);
> +      /* The constructed object might require a cleanup.  */
> +      if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (gro_type))
> +	{
> +	  tree cleanup
> +	    = build_special_member_call (gro, complete_dtor_identifier,
> +					 NULL, gro_type, LOOKUP_NORMAL,
> +					 tf_warning_or_error);
> +	  gro_cleanup_stmt = build_stmt (input_location, CLEANUP_STMT, NULL,
> +					 cleanup, gro);
> +	}
>       }
> +  finish_expr_stmt (r);
> +
> +  if (gro_cleanup_stmt)
> +    CLEANUP_BODY (gro_cleanup_stmt) = push_stmt_list ();
>   
>     /* Initialize the resume_idx_name to 0, meaning "not started".  */
>     tree resume_idx_m
> @@ -4349,14 +4384,15 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>        promise was constructed.  We now supply a reference to that var,
>        either as the return value (if it's the same type) or to the CTOR
>        for an object of the return type.  */
> -  if (gro_is_void_p)
> -    r = NULL_TREE;
> -  else
> -    r = rvalue (gro);
>   
> -  if (!same_type_p (gro_type, fn_return_type))
> +  if (same_type_p (gro_type, fn_return_type))
> +    r = gro_is_void_p ? NULL_TREE : DECL_RESULT (orig);
> +  else
>       {
> -      /* The return object is , even if the gro is void.  */
> +      /* If we have void gro and a non-class return type, then pick a
> +	 defensive initialisation value.  */
> +      r = gro_is_void_p ? integer_zero_node : rvalue (gro);
> +      /* The return object is constructed, even if the gro is void.  */

Would error_mark_node work here?  I presume we've already diagnosed the 
problem, so will result in no cascade of errors.

>         if (CLASS_TYPE_P (fn_return_type))
>   	{
>   	  vec<tree, va_gc> *args = NULL;
> @@ -4374,12 +4410,19 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   	  if (args)
>   	    release_tree_vector (args);
>   	}
> -      else /* ??? suppose we have non-class return and void gro?  */
> +      else
>   	r = build1_loc (input_location, CONVERT_EXPR, fn_return_type, r);
>       }
>   
>     finish_return_stmt (r);
>   
> +  if (gro_cleanup_stmt)
> +    {
> +      CLEANUP_BODY (gro_cleanup_stmt)
> +        = pop_stmt_list (CLEANUP_BODY (gro_cleanup_stmt));
> +      add_stmt (gro_cleanup_stmt);
> +    }
> +
>     /* Finish up the ramp function.  */
>     BIND_EXPR_VARS (gro_context_bind) = gro_bind_vars;
>     BIND_EXPR_BODY (gro_context_bind) = pop_stmt_list (gro_context_body);
> diff --git a/gcc/testsuite/g++.dg/coroutines/pr95477.C b/gcc/testsuite/g++.dg/coroutines/pr95477.C
> new file mode 100644
> index 00000000000..7050aee0078
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/coroutines/pr95477.C
> @@ -0,0 +1,37 @@
> +//  { dg-do run }
> +
> +#include "coro.h"
> +
> +struct simple {
> +  static inline int alive = 0;
> +  simple() { ++alive; }
> +  simple(simple&&) { ++alive; }
> +  ~simple() { --alive; }
> +
> +  struct promise_type {
> +    simple get_return_object() { return simple{}; }
> +    void return_void() {}
> +    void unhandled_exception() {}
> +    auto initial_suspend() noexcept { return coro::suspend_never{}; }
> +    auto final_suspend() noexcept { return coro::suspend_never{}; }
> +  };
> +};
> +
> +simple
> +f()
> +{
> +  co_return;
> +}
> +
> +int main() {
> +  {
> +    f();
> +  }
> +
> +  if (simple::alive != 0)
> +   {
> +     PRINTF ("something wrong with dtors: %d\n", simple::alive);
> +     abort ();
> +   }
> +  return 0;
> +}
> 


-- 
Nathan Sidwell