From: Jonathan Wakely <jwakely@redhat.com>
To: "François Dumont" <frs.dumont@gmail.com>
Cc: "libstdc++@gcc.gnu.org" <libstdc++@gcc.gnu.org>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Help compiler detect invalid code
Date: Fri, 27 Sep 2019 11:24:00 -0000 [thread overview]
Message-ID: <20190927112424.GV9487@redhat.com> (raw)
In-Reply-To: <96b51704-67fe-3ac4-405c-6997151d926c@gmail.com>
On 20/09/19 07:08 +0200, François Dumont wrote:
>I already realized that previous patch will be too controversial to be
>accepted.
>
>In this new version I just implement a real memmove in __memmove so
A real memmove doesn't just work backwards, it needs to detect any
overlaps and work forwards *or* backwards, as needed.
I think your change will break this case:
#include <algorithm>
constexpr int f(int i, int j, int k)
{
int arr[5] = { 0, 0, i, j, k };
std::move(arr+2, arr+5, arr);
return arr[0] + arr[1] + arr[2];
}
static_assert( f(1, 2, 3) == 6 );
This is valid because std::move only requires that the result iterator
is not in the input range, but it's OK for the two ranges to overlap.
I haven't tested it, but I think with your change the array will end
up containing {3, 2, 3, 2, 3} instead of {1, 2, 3, 2, 3}.
next prev parent reply other threads:[~2019-09-27 11:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 20:28 François Dumont
2019-09-20 5:08 ` François Dumont
2019-09-25 20:40 ` François Dumont
2019-09-27 11:24 ` Jonathan Wakely [this message]
2019-10-01 20:05 ` François Dumont
2019-10-10 20:03 ` Jonathan Wakely
2019-10-16 20:22 ` François Dumont
2019-09-27 12:11 ` Jonathan Wakely
2019-09-27 16:24 ` François Dumont
2019-09-27 16:45 ` Jonathan Wakely
2019-09-28 21:12 ` [PATCH] Fix algo constexpr tests in Debug mode François Dumont
2019-09-30 9:03 ` Jonathan Wakely
2019-09-30 20:21 ` François Dumont
2019-10-01 11:21 ` Jonathan Wakely
2019-10-23 15:26 ` Jonathan Wakely
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