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From: "rhalbersma at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/113806] New: [performance] bitset::operator>>=
 unnecessarily sanitizes the high-word
Date: Wed, 07 Feb 2024 12:21:46 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113806

            Bug ID: 113806
           Summary: [performance] bitset::operator>>=3D unnecessarily
                    sanitizes the high-word
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rhalbersma at gmail dot com
  Target Milestone: ---

It seems that since time immemorial, bitset::operator>>=3D unnecessarily
sanitizes the high word by calling this->_M_do_sanitize();=20

It is unnecessary since right-shifting moves bits away from the high-word so
that the class invariant can not be violated (in contrast to
bitset::operator<<=3D where bits flow into the high word, and where t).=20

Current LOC is 1092 in <bitset> on libstdc++ trunk, and could be removed wi=
th
no functional change.=