From: Jason Merrill <jason@redhat.com>
To: Kai Tietz <ktietz70@googlemail.com>
Cc: Kai Tietz <ktietz@redhat.com>,
gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: C++ delayed folding branch review
Date: Mon, 03 Aug 2015 15:39:00 -0000 [thread overview]
Message-ID: <55BF8B2B.9040001@redhat.com> (raw)
In-Reply-To: <CAEwic4aQeu6c88q+RfZ=mGu6tObjzq9tWR4YgRnxCjk2PG=cXQ@mail.gmail.com>
On 08/03/2015 05:42 AM, Kai Tietz wrote:
> 2015-08-03 5:49 GMT+02:00 Jason Merrill <jason@redhat.com>:
>> On 07/31/2015 05:54 PM, Kai Tietz wrote:
>>>
>>> The "STRIP_NOPS-requirement in 'reduced_constant_expression_p'" I could
>>> remove, but for one case in constexpr. Without folding we don't do
>>> type-sinking/raising.
>>
>>
>> Right.
>>
>>> So binary/unary operations might be containing cast, which were in the
>>> past unexpected.
>>
>> Why aren't the casts folded away?
>
> On such cast constructs, as for this vector-sample, we can't fold away
Which testcase is this?
> the cast chain. The difference here to none-delayed-folding branch is
> that the cast isn't moved out of the plus-expr. What we see now is
> (plus ((vec) (const vector ...) { .... }), ...). Before we had (vec)
> (plus (const vector ...) { ... }).
How could a PLUS_EXPR be considered a reduced constant, regardless of
where the cast is?
>>> On verify_constant we check by reduced_constant_expression_p, if value is
>>> a constant. We don't handle here, that NOP_EXPRs are something we want to
>>> look through here, as it doesn't change anything if this is a constant, or
>>> not.
>>
>> NOPs around constants should have been folded away by the time we get there.
>
> Not in this cases, as the we actually have here a switch from const to
> none-const. So there is an attribute-change, which we can't ignore in
> general.
I wasn't suggesting we ignore it, we should be able to change the type
of the vector_cst.
> But I agree that for constexpr's we could special case cast
> from const to none-const (as required in expressions like const vec v
> = v + 1).
Right. But really this should happen in convert.c, it shouldn't be
specific to C++.
Jason
next prev parent reply other threads:[~2015-08-03 15:39 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-12 5:41 Jason Merrill
2015-06-12 16:17 ` Kai Tietz
2015-06-13 7:58 ` Jason Merrill
2015-07-27 19:01 ` Jason Merrill
2015-07-28 2:40 ` Kai Tietz
2015-07-28 20:35 ` Kai Tietz
2015-07-29 18:48 ` Jason Merrill
2015-07-29 23:03 ` Kai Tietz
2015-07-30 14:40 ` Kai Tietz
2015-07-30 18:41 ` Jason Merrill
2015-07-30 21:33 ` Kai Tietz
2015-07-31 0:43 ` Jason Merrill
2015-07-31 7:08 ` Jeff Law
2015-07-31 23:00 ` Kai Tietz
2015-08-03 3:49 ` Jason Merrill
2015-08-03 9:42 ` Kai Tietz
2015-08-03 15:39 ` Jason Merrill [this message]
2015-08-24 7:20 ` Kai Tietz
2015-08-27 2:57 ` Jason Merrill
2015-08-27 10:54 ` Kai Tietz
2015-08-27 13:35 ` Jason Merrill
2015-08-27 13:44 ` Kai Tietz
2015-08-27 18:15 ` Kai Tietz
2015-08-28 3:03 ` Jason Merrill
2015-08-28 7:43 ` Kai Tietz
2015-08-28 11:18 ` Kai Tietz
2015-08-28 2:12 ` Jason Merrill
2015-07-31 4:00 ` Jeff Law
2015-07-31 16:26 ` Jason Merrill
2015-07-31 16:43 ` Kai Tietz
2015-07-31 16:52 ` Jakub Jelinek
2015-07-31 16:53 ` Jason Merrill
2015-07-31 21:31 ` Kai Tietz
-- strict thread matches above, loose matches on Subject: below --
2015-04-24 4:23 Jason Merrill
2015-04-24 13:46 ` Kai Tietz
2015-04-24 18:25 ` Jason Merrill
2015-04-28 12:06 ` Kai Tietz
2015-04-28 13:57 ` Jason Merrill
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