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 target/99434] std::bit_cast generates more instructions than __builtin_bit_cast and memcpy with -march=native
Date: Mon, 08 Mar 2021 16:50:21 +0000	[thread overview]
Message-ID: <bug-99434-4-kihIZQhmPn@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-99434-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99434

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Testcase without includes:
template<typename _To, typename _From>
constexpr _To
bit_cast(const _From& __from) noexcept
{
  return __builtin_bit_cast(_To, __from);
}

struct u64x2_t
{
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
  unsigned long long high,low;
#else
  unsigned long long low,high;
#endif
};
u64x2_t umul5(unsigned long long a,unsigned long long b) noexcept
{
  return bit_cast<u64x2_t>(static_cast<__uint128_t>(a)*b);
}

u64x2_t umul_builtin(unsigned long long a,unsigned long long b) noexcept
{
  return __builtin_bit_cast(u64x2_t,static_cast<__uint128_t>(a)*b);
}

  parent reply	other threads:[~2021-03-08 16:50 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-06 20:12 [Bug tree-optimization/99434] New: " unlvsur at live dot com
2021-03-06 21:25 ` [Bug target/99434] " pinskia at gcc dot gnu.org
2021-03-06 21:36 ` unlvsur at live dot com
2021-03-06 22:50 ` pinskia at gcc dot gnu.org
2021-03-08 16:49 ` jakub at gcc dot gnu.org
2021-03-08 16:50 ` jakub at gcc dot gnu.org [this message]
2021-03-08 20:40 ` unlvsur at live 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-99434-4-kihIZQhmPn@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).