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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/98465] [11 Regression] Bogus -Wstringop-overread with -std=gnu++20 -O2 and std::string::insert
Date: Thu, 04 Feb 2021 16:58:08 +0000 [thread overview]
Message-ID: <bug-98465-4-OSJINkNFAH@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98465-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98465
--- Comment #24 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ok, so for GCC 11, can we just help the optimizers a little bit and at the same
time get rid of the warning?
Like:
--- libstdc++-v3/include/bits/basic_string.tcc.jj 2021-01-04
10:26:02.930960956 +0100
+++ libstdc++-v3/include/bits/basic_string.tcc 2021-02-04 17:44:10.592843195
+0100
@@ -477,7 +477,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
if (__s + __len2 <= __p + __len1)
this->_S_move(__p, __s, __len2);
+#if _GLIBCXX_HAS_BUILTIN(__builtin_object_size) && defined(__OPTIMIZE__)
+ /* Help the optimizers rule out impossible cases and
+ get rid of false positive warnings at the same time.
+ If we know the maximum size of the __s object and
+ it is shorter than 2 * __len2 - __len1, then
+ __s >= __p + __len1 case is impossible. */
+ else if (!(__builtin_constant_p((2 * __len2 - __len1)
+ * sizeof(_CharT))
+ && __builtin_object_size(__s, 0)
+ < (2 * __len2 - __len1) * sizeof(_CharT))
+ && __s >= __p + __len1)
+#else
else if (__s >= __p + __len1)
+#endif
this->_S_copy(__p, __s + __len2 - __len1, __len2);
else
{
I don't get the warning anymore and function size on #c0 testcase shrunk with
-O2 -std=gnu++20 -Wall from 614 bytes to 568.
This code is handling the non-disjunct case, and when __s >= __p + __len1 and
__len1 < __len2, we need to copy from (__s + __len2 - __len1) __len2, i.e. have
access up to __s + 2 * __len2 - __len1 - 1. If we know that is certainly out
of bounds, most likely it isn't the non-disjunct case at all, but even if it
would, this copying wouldn't be a valid option.
next prev parent reply other threads:[~2021-02-04 16:58 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-28 18:36 [Bug middle-end/98465] New: Bogus warning stringop-overread wuth " romain.geissler at amadeus dot com
2020-12-28 20:54 ` [Bug middle-end/98465] " msebor at gcc dot gnu.org
2020-12-30 12:49 ` romain.geissler at amadeus dot com
2020-12-30 13:22 ` romain.geissler at amadeus dot com
2020-12-30 21:25 ` msebor at gcc dot gnu.org
2021-01-06 22:38 ` msebor at gcc dot gnu.org
2021-01-06 22:59 ` msebor at gcc dot gnu.org
2021-01-06 23:14 ` msebor at gcc dot gnu.org
2021-01-07 20:26 ` msebor at gcc dot gnu.org
2021-01-13 18:19 ` msebor at gcc dot gnu.org
2021-01-13 18:41 ` law at redhat dot com
2021-01-13 18:52 ` jakub at gcc dot gnu.org
2021-01-13 19:02 ` msebor at gcc dot gnu.org
2021-01-13 19:14 ` jakub at gcc dot gnu.org
2021-01-13 19:30 ` msebor at gcc dot gnu.org
2021-01-14 2:21 ` msebor at gcc dot gnu.org
2021-01-19 19:00 ` msebor at gcc dot gnu.org
2021-01-20 23:20 ` [Bug middle-end/98465] [11 Regression] Bogus -Wstringop-overread with " msebor at gcc dot gnu.org
2021-02-04 14:03 ` jakub at gcc dot gnu.org
2021-02-04 14:39 ` redi at gcc dot gnu.org
2021-02-04 15:25 ` jakub at gcc dot gnu.org
2021-02-04 15:53 ` redi at gcc dot gnu.org
2021-02-04 15:54 ` redi at gcc dot gnu.org
2021-02-04 16:02 ` msebor at gcc dot gnu.org
2021-02-04 16:58 ` jakub at gcc dot gnu.org [this message]
2021-02-04 17:12 ` jakub at gcc dot gnu.org
2021-02-04 20:57 ` msebor at gcc dot gnu.org
2021-02-04 21:09 ` jakub at gcc dot gnu.org
2021-02-05 10:15 ` jakub at gcc dot gnu.org
2021-02-08 18:51 ` jakub at gcc dot gnu.org
2021-02-09 11:33 ` cvs-commit at gcc dot gnu.org
2021-02-09 11:35 ` [Bug middle-end/98465] " jakub at gcc dot gnu.org
2021-02-19 23:41 ` msebor at gcc dot gnu.org
2021-11-12 19:53 ` msebor at gcc dot gnu.org
2022-02-15 3:55 ` Randy at miningrigrentals dot com
2022-02-15 9:47 ` redi at gcc dot gnu.org
2022-02-15 9:55 ` Randy at miningrigrentals dot com
2022-02-15 10:02 ` redi at gcc dot gnu.org
2022-02-15 10:50 ` Randy at miningrigrentals dot com
2022-02-15 12:29 ` redi at gcc dot gnu.org
2022-02-15 12:40 ` Randy at miningrigrentals dot com
2022-02-15 12:52 ` redi at gcc dot gnu.org
2022-02-15 19:23 ` Randy at miningrigrentals dot com
2022-02-17 10:37 ` redi at gcc dot gnu.org
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