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From: "vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/94337] New: Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning Date: Thu, 26 Mar 2020 02:03:46 +0000 [thread overview] Message-ID: <bug-94337-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94337 Bug ID: 94337 Summary: Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: vincent-gcc at vinc17 dot net Target Milestone: --- Consider the following example. #include <stdio.h> struct s1 { int a; }; struct s2 { int a, b; }; int main (void) { union { struct s1 m1[1]; struct s2 m2[1]; } u; (u.m2)->b = 17; printf ("%d\n", ((struct s2 *) (struct s1 *) u.m2)->b); printf ("%d\n", ((struct s2 *) u.m1)->b); return 0; } zira:~> gcc-10 tst.c -o tst -O2 -Wstrict-aliasing tst.c: In function ‘main’: tst.c:22:20: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] 22 | printf ("%d\n", ((struct s2 *) u.m1)->b); | ~^~~~~~~~~~~~~~~~~~~ But there is no type-punning here. All accesses are done via struct s2. Everything else is pointer conversions, which are not related to the aliasing rules.
next reply other threads:[~2020-03-26 2:03 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-26 2:03 vincent-gcc at vinc17 dot net [this message] 2020-03-26 7:03 ` [Bug c/94337] " rguenth at gcc dot gnu.org 2020-03-26 9:12 ` vincent-gcc at vinc17 dot net
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