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From: Iain Sandoe <>
To: Jason Merrill <>
Cc: GCC Patches <>
Subject: Re: [PATCH RFC] c++: fix broken conversion in coroutines
Date: Thu, 6 Oct 2022 23:47:26 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

> On 6 Oct 2022, at 22:44, Jason Merrill <> wrote:
> On 10/3/22 23:53, Jason Merrill wrote:
>> On 9/30/22 18:50, Iain Sandoe wrote:
>>> Hi Jason,
>>>> On 30 Sep 2022, at 23:06, Jason Merrill <> 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).
>> The problem is you're treating one class directly as another class here, without the indirection involved in usual type-erasure idioms.
>> It does seem that the gimplifier handles this fine, but it doesn't correspond to anything in the language and much of the front end assumes that CONVERT_EXPR is only used for scalars.  VIEW_CONVERT_EXPR would better express that we're not doing anything to the value, just cheating the type system.  That's still dodgy from a language perspective, but probably safe enough in this case.
> So I'm applying this:<0001-c-fix-broken-conversion-in-coroutines.patch>

thanks, I have not had any cycles to look at this.

however, when I next do - was planning on looking at the:
cont = handle.from_address(await_suspend().address())
approach, since both .address() and .from_address() are constexpr, cp_fold_function should turn that into essentially a NOP.

      reply	other threads:[~2022-10-06 22:47 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-30 22:06 Jason Merrill
2022-09-30 22:50 ` Iain Sandoe
2022-10-04  3:53   ` Jason Merrill
2022-10-06 21:44     ` Jason Merrill
2022-10-06 22:47       ` Iain Sandoe [this message]

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