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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/115160] Enabling undefined behaviour sanitizer causes or'ed bit shift to report wrong result Date: Mon, 20 May 2024 17:56:24 +0000 [thread overview] Message-ID: <bug-115160-4-qwBdMwacqi@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-115160-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115160 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID CC| |jakub at gcc dot gnu.org --- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- This is just bogus testcase, anything can happen. If you use unsigned char data[] = { 1, 0, 0, 0 }, *b = data; instead of the std::vector<uint8_t> data; data.emplace_back(1); data.emplace_back(0); data.emplace_back(0); data.emplace_back(0); auto b = data.begin(); lines, g++ -Wall diagnoses it: pr115160.C: In function ‘int main()’: pr115160.C:12:50: warning: operation on ‘b’ may be undefined [-Wsequence-point] 12 | std::cout << (int)( (*b++) | (*b++ << 8) | (*b++ << 16 ) | ( *b << 24 ) )<< std::endl; | ~^~ pr115160.C:12:50: warning: operation on ‘b’ may be undefined [-Wsequence-point] pr115160.C:12:50: warning: operation on ‘b’ may be undefined [-Wsequence-point] pr115160.C:12:50: warning: operation on ‘b’ may be undefined [-Wsequence-point] While https://wg21.link/p0145r3 in C++17 made evaluation order in some cases well defined, it certainly didn't do that for non-overloaded operator| or similar operators.
next prev parent reply other threads:[~2024-05-20 17:56 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-05-20 10:03 [Bug c++/115160] New: " raanan.lori at getnexar dot com 2024-05-20 17:56 ` jakub at gcc dot gnu.org [this message] 2024-05-21 9:41 ` [Bug c++/115160] " raanan.lori at getnexar dot com 2024-05-21 9:53 ` jakub at gcc dot gnu.org 2024-05-21 10:07 ` raanan.lori at getnexar dot com 2024-05-21 11:46 ` redi at gcc dot gnu.org 2024-05-21 12:09 ` jakub at gcc dot gnu.org
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