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From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/116316] New: incorrect code with -O2
Date: Fri, 09 Aug 2024 18:42:36 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 15.0
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X-Bugzilla-Who: qinzhao at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D116316

            Bug ID: 116316
           Summary: incorrect code with -O2
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qinzhao at gcc dot gnu.org
  Target Milestone: ---

the following testing case failed on both x86 and aarch64 with -O2, but pas=
sed
with -O1:

#include <stdio.h>
struct annotated {
  int b;
  int c[];
} *array_annotated;

int main(int argc, char *argv[])
{
  size_t __size =3D sizeof(struct annotated) + sizeof(*array_annotated->c) =
* 10;
  array_annotated =3D (struct annotated *) __builtin_malloc(__size);
  __builtin_memset(array_annotated, 0, __size);
  if (&(array_annotated->b))
    *(size_t *)(&(array_annotated->b)) =3D 10;
  if (array_annotated->b !=3D 10)
    __builtin_abort ();

  printf("pass\n");
  return 0;
}


adding -fno-tree-fre -fno-tree-pre -fno-code-hoisting cures the issue

[opc@qinzhao-aarch64-ol8 ~]$ ./Install/latest-d/bin/gcc t.c -O2
[opc@qinzhao-aarch64-ol8 ~]$ ./a.out
Aborted (core dumped)
[opc@qinzhao-aarch64-ol8 ~]$ ./Install/latest-d/bin/gcc t.c -O2 -fno-tree-f=
re
-fno-tree-pre -fno-code-hoisting
[opc@qinzhao-aarch64-ol8 ~]$ ./a.out
pass=