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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/110557] New: Wrong code for x86_64-linux-gnu with -O3 -mavx2: vectorized loop mishandles signed bit-fields Date: Wed, 05 Jul 2023 11:10:20 +0000 [thread overview] Message-ID: <bug-110557-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110557 Bug ID: 110557 Summary: Wrong code for x86_64-linux-gnu with -O3 -mavx2: vectorized loop mishandles signed bit-fields Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: xry111 at gcc dot gnu.org Target Milestone: --- $ cat test.cc #include <cstddef> size_t max(size_t a, size_t b) { return a < b ? b : a; } struct Item { int x : 8; std::ptrdiff_t y : 56; }; __attribute__((noipa)) std::size_t test(Item *a, int cnt) { std::size_t size = 0; for (int i = 0; i < cnt; i++) size = max(static_cast<size_t>(-(a[i].y * 4)), size); return size; } int main() { struct Item items[] = { {1, -1}, {2, -2}, {3, -3}, {4, -4}, }; if (test(items, 4) != 16) __builtin_trap(); } $ g++ test.cc -Wall -Wextra -O3 -fsanitize=undefined $ ./a.out && echo ok ok $ g++ test.cc -Wall -Wextra -O3 -mavx2 $ ./a.out && echo ok Illegal instruction (core dumped) Reproducible with GCC 13.1 and trunk. Interestingly if I convert the test case to C (instead of C++) the issue won't reproduce. This test case is reduced from WebKit, it crashes with GCC 13.1 and -O3 -mavx2. The WebKit code has "<< 2" instead of "* 4", thus invoking an undefined behavior. But it still crashes even if I change "<< 2" to "* 4".
next reply other threads:[~2023-07-05 11:10 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-07-05 11:10 xry111 at gcc dot gnu.org [this message] 2023-07-05 11:11 ` [Bug target/110557] [13/14 Regression] " xry111 at gcc dot gnu.org 2023-07-05 13:15 ` [Bug tree-optimization/110557] " pinskia at gcc dot gnu.org 2023-07-06 8:17 ` rguenth at gcc dot gnu.org 2023-07-06 10:17 ` avieira at gcc dot gnu.org 2023-07-06 10:21 ` xry111 at gcc dot gnu.org 2023-07-06 11:30 ` xry111 at gcc dot gnu.org 2023-07-06 14:58 ` avieira at gcc dot gnu.org 2023-07-06 16:18 ` xry111 at gcc dot gnu.org 2023-07-06 16:32 ` xry111 at gcc dot gnu.org 2023-07-10 10:36 ` cvs-commit at gcc dot gnu.org 2023-07-10 10:36 ` cvs-commit at gcc dot gnu.org 2023-07-10 10:38 ` xry111 at gcc dot gnu.org 2023-07-11 8:16 ` xry111 at gcc dot gnu.org
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