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From: "jwzeng at nuaa dot edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/112344] New: [14 Regression] Wrong code at -O2 on
 x86_64-pc-linux-gnu
Date: Thu, 02 Nov 2023 06:30:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112344

            Bug ID: 112344
           Summary: [14 Regression] Wrong code at -O2 on
                    x86_64-pc-linux-gnu
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jwzeng at nuaa dot edu.cn
  Target Milestone: ---

I compiled the following code with gcc at -O2, and it produces the wrong co=
de.=20

The correct output result should be 13, but 73 was output under -O2.=20

This bug seems to only exist on gcc-trunk. The gcc-tk used below is the
earliest version I can use that triggers this bug.

Compiler explorer: https://godbolt.org/z/8hq64asT5

```c
$ cat test.c
int printf(const char *, ...);
int a;
void b() {
  long c =3D 3;
  unsigned int d =3D 50253292;
  int e =3D 2147483648;
  for (; a < 5; a++)
    do {
      e +=3D 4;
      d -=3D c;
    } while (e < 20);
  printf("%d\n", d);
}
int main() { b(); }
$
$ gcc-tk test.c -O2; ./test.c
73
$
$ gcc-tk test.c -O0; ./test.c
13
$ gcc-tk test.c -O1; ./test.c
13
$ gcc-tk test.c -O3; ./test.c
13
$ gcc-tk test.c -Os; ./test.c
13
$ ccomp test.c -O1; ./a.out
13
$
$ gcc-tk --version
gcc (GCC) 14.0.0 20230922 (experimental) [master r14-4213-gd35e12e1c0]
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$
$ ccomp --version
The CompCert C verified compiler, version 3.12
```=