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From: "tangyixuan at mail dot dlut.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115582] New: [regression 15] wrong code when
 accessing members of incompatible type structure
Date: Fri, 21 Jun 2024 13:48:52 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 15.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115582

            Bug ID: 115582
           Summary: [regression 15] wrong code when accessing members of
                    incompatible type structure
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tangyixuan at mail dot dlut.edu.cn
  Target Milestone: ---

Hi, I find GCC produces wrong code under optimizations when pointers point =
to
incompatible type structure but the member types are compatible.

Compiler Explorer: https://godbolt.org/z/jjY599Yfe

$ cat s.c

int printf(const char *, ...);
struct s {int x; } __attribute__((packed));
struct t {int x; };

void swap(struct s* p, struct t* q)
{
  p->x =3D q->x;
  q->x =3D p->x;
}
int main()
{=20=20=20=20
  struct t a[2];
  a[0].x =3D 1234;
  a[1].x =3D 5678;
  swap ((struct s *)((char *)a + 1), a);
  printf("%d",a[0].x);
  return 0;
}=