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List:       gcc-patches
Subject:    Re: [PATCH RFC] c++: fix broken conversion in coroutines
From:       Iain Sandoe <iain () sandoe ! co ! uk>
Date:       2022-09-30 22:50:03
Message-ID: 219253A3-8202-4286-9621-982BC5CD24DF () sandoe ! co ! uk
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Hi Jason,

> On 30 Sep 2022, at 23:06, Jason Merrill <jason@redhat.com> wrote:
> 
> You can't use CONVERT_EXPR to convert between two class types, and it was
> breaking copy elision.
> 
> Unfortunately, this patch breaks symmetric-transfer-00-basic.C, where
> susp_type is Loopy<int>::handle_type.  How is this supposed to work?

We are trying to save a type-erased handle (which the symmetric transfer makes
and indirect call through, nothing else).

so, I suppose the equivalent could be:

conthand = coroutine_handle::from_address (suspend.address())

or, is there some cast version that would be valid here?
Iain

> 
> gcc/cp/ChangeLog:
> 
> 	* coroutines.cc (expand_one_await_expression): Change conversion
> 	to assert.
> ---
> gcc/cp/coroutines.cc | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index eca01abcb7a..568f2edf67d 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -1728,7 +1728,9 @@ expand_one_await_expression (tree *stmt, tree *await_expr, void *d)
>     }
>   else
>     {
> -      r = build1_loc (loc, CONVERT_EXPR, void_coro_handle_type, suspend);
> +      gcc_checking_assert (same_type_ignoring_top_level_qualifiers_p
> +			   (void_coro_handle_type, susp_type));
> +      r = suspend;
>       r = build2_loc (loc, INIT_EXPR, void_coro_handle_type, data->conthand, r);
>       r = build1 (CONVERT_EXPR, void_type_node, r);
>       append_to_statement_list (r, &body_list);
> 
> base-commit: 43faf3e5445b571731e52faa1be085ecd0a09323
> -- 
> 2.31.1
> 

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