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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/103534] [12 regression] Spurious -Wstringop-overflow warning with std::string concatencation
Date: Thu, 02 Dec 2021 21:53:01 +0000 [thread overview]
Message-ID: <bug-103534-4-O4desJJiQn@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-103534-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103534
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |alias, missed-optimization
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note there is one missing optimization:
D.42086._M_string_length = 0;
MEM[(char_type &)&D.42086 + 16] = 0;
MEM[(struct basic_string *)&D.41925] ={v} {CLOBBER};
MEM[(struct _Alloc_hider *)&D.41925] ={v} {CLOBBER};
MEM[(struct _Alloc_hider *)&D.41925]._M_p = &D.41925.D.33308._M_local_buf;
_69 = operator new (17);
<bb 3> [local count: 1003797485]:
D.41925._M_dataplus._M_p = _69;
D.41925.D.33308._M_allocated_capacity = 16;
__builtin_memcpy (_69, "1234567890123456", 16);
D.41925._M_string_length = 16;
MEM[(char_type &)_69 + 16] = 0;
_75 = D.42086._M_string_length;
__size_76 = _75 + 16;
pretmp_56 = D.42086._M_dataplus._M_p;
if (__size_76 > 16)
goto <bb 4>; [67.00%]
else
goto <bb 12>; [33.00%]
This might be related to that GCC does not handle the operator new better.
Obvious if that missed optimization is fixed, then the warning will be gone.
I also noticed that with -std=c++17 (or before), the constructor for
std::string is not inlined fully for both std::string objects which avoids the
false positive.
This is another case where it is a "maybe" exceeds maximum object size and we
need to come up with a solution for it.
next prev parent reply other threads:[~2021-12-02 21:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-02 19:47 [Bug c++/103534] New: " sss@li-snyder.org
2021-12-02 21:03 ` [Bug c++/103534] " msebor at gcc dot gnu.org
2021-12-02 21:53 ` pinskia at gcc dot gnu.org [this message]
2021-12-02 23:02 ` redi at gcc dot gnu.org
2021-12-02 23:19 ` msebor at gcc dot gnu.org
2021-12-06 8:16 ` rguenth at gcc dot gnu.org
2021-12-10 16:29 ` jason at gcc dot gnu.org
2021-12-10 16:30 ` jason at gcc dot gnu.org
2021-12-10 16:37 ` jason at gcc dot gnu.org
2021-12-10 16:53 ` msebor at gcc dot gnu.org
2021-12-10 17:04 ` jakub at gcc dot gnu.org
2021-12-11 4:58 ` cvs-commit at gcc dot gnu.org
2021-12-13 16:11 ` jason at gcc dot gnu.org
2021-12-13 16:11 ` jason at gcc dot gnu.org
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