coroutines: Handle lambda closure pointers like 'this'.

Hi,

We didn’t quite have time to push this through before the 10.1
deadline, but (since it’s a correctness issue) it should be applied
to the branch too.

tested on x86_64-darwin, linux
OK for master?
10.2 after some bake time?
thanks
Iain

=======

It was agreed amongst the implementors that the correct
interpretation of the standard is that lambda closure pointers
should be treated in the same manner as class object pointers.

gcc/cp/ChangeLog:

	* coroutines.cc (instantiate_coro_traits): Pass a reference
	to lambda closure objects to traits instantiation.
	(morph_fn_to_coro): Likewise for promise parameter
	preview and allocator lookup.
---
 gcc/cp/coroutines.cc | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

On 5/22/20 8:27 AM, Iain Sandoe wrote:
> Hi,
> 
> We didn’t quite have time to push this through before the 10.1
> deadline, but (since it’s a correctness issue) it should be applied
> to the branch too.
> 
> tested on x86_64-darwin, linux
> OK for master?
> 10.2 after some bake time?
> thanks
> Iain
> 
> =======
> 
> It was agreed amongst the implementors that the correct
> interpretation of the standard is that lambda closure pointers
> should be treated in the same manner as class object pointers.
> 
> gcc/cp/ChangeLog:
> 
> 	* coroutines.cc (instantiate_coro_traits): Pass a reference
> 	to lambda closure objects to traits instantiation.
> 	(morph_fn_to_coro): Likewise for promise parameter
> 	preview and allocator lookup.
> ---
>   gcc/cp/coroutines.cc | 19 +++++--------------
>   1 file changed, 5 insertions(+), 14 deletions(-)
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index b79e2c66b70..6e3f03bdb0d 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -304,8 +304,8 @@ instantiate_coro_traits (tree fndecl, location_t kw)
>   
>     while (arg_node != NULL_TREE && !VOID_TYPE_P (TREE_VALUE (arg_node)))
>       {
> -      /* See PR94807, as to why we must exclude lambda here.  */
> -      if (is_this_parameter (arg) && !lambda_p)
> +      if (is_this_parameter (arg)
> +	  || (lambda_p && DECL_NAME (arg) == closure_identifier))

DECL_NAME (arg) == closure_identifier is sufficient -- it's in the 
implementor's namespace.  Just like how is_this_parameter works. (that I 
fixed trunk to not label a lambda's instantiation a this pointer doesn't 
matter here, so you don't have to account for it not being so on 10.2).

>   	{
>   	  /* We pass a reference to *this to the param preview.  */
>   	  tree ct = TREE_TYPE (TREE_TYPE (arg));
> @@ -3793,13 +3793,8 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
>   	    parm.frame_type = actual_type;
>   
>   	  parm.this_ptr = is_this_parameter (arg);
> -	  /* See PR94807.  When a lambda is in a template instantiation, the
> -	     closure object is named 'this' instead of '__closure'.  */
>   	  if (lambda_p)
> -	    {
> -	      parm.lambda_cobj = DECL_NAME (arg) == closure_identifier;
> -	      gcc_checking_assert (!parm.this_ptr);
> -	    }
> +	    parm.lambda_cobj = DECL_NAME (arg) == closure_identifier;

but this bit will be different on 10.2.  I think you want
if (lambda_p)
  { parm.lambda_cobj = parm.this_ptr || DECL_NAME (arg) == 
closure_identifier;
    parm.this_pointer = false;
}
?


looks ok otherwise, for both.