public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/86369] constexpr const char* comparison fails
Date: Thu, 05 Aug 2021 18:09:16 +0000	[thread overview]
Message-ID: <bug-86369-4-4k6HxpgHvH@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-86369-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86369

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Another possibility would be to detect it in cxx_eval_binary_expression before
calling fold_binary_loc and punt.

But, the constant evaluation actually doesn't track whether it is the same or
different evaluation of the same string literal, so not optimizing it would on
the other side mean we'd reject valid code.  Consider

constexpr auto name3(const char *p) { return p; }

int main() {
    constexpr auto p1 = "test3";
    constexpr auto p2 = "test4";
    constexpr auto b1 = (name3(p1) == name3(p1)); // should be true
    constexpr auto b2 = (name3(p1) == name3(p2)); // should be false
}

Note, latest clang++ seems to accept b1 in both #c0 and #c6 testcases and
reject b2 in both.

  parent reply	other threads:[~2021-08-05 18:09 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-86369-4@http.gcc.gnu.org/bugzilla/>
2021-08-05  4:43 ` pinskia at gcc dot gnu.org
2021-08-05 15:24 ` redi at gcc dot gnu.org
2021-08-05 15:30 ` jakub at gcc dot gnu.org
2021-08-05 18:09 ` jakub at gcc dot gnu.org [this message]
2021-08-06  7:27 ` rguenth at gcc dot gnu.org
2022-01-18 13:18 ` jason at gcc dot gnu.org
2022-11-04 13:10 ` aaron at aaronballman dot com
2022-11-04 13:27 ` jakub at gcc dot gnu.org
2022-11-04 13:53 ` aaron at aaronballman dot com

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-86369-4-4k6HxpgHvH@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).