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From: "jwzeng at nuaa dot edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110410] New: [14 Regression] Different
 results between -O0 and -O2
Date: Mon, 26 Jun 2023 09:38:55 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: jwzeng at nuaa dot edu.cn
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110410

            Bug ID: 110410
           Summary: [14 Regression] Different results between -O0 and -O2
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jwzeng at nuaa dot edu.cn
  Target Milestone: ---

The following code snippet:

#include <stdio.h>
int seed;
void hash(int *seed, int v) { *seed ^=3D v; }
unsigned int var_6 =3D 1341494070U;
int var_7 =3D 0;
unsigned short var_8 =3D 7472;
int var_13 =3D 518868156U;
unsigned var_17;
#define min(a, b) ((a) < (b) ? (a) : (b))
void test() {
    for (int ii_0 =3D 0; ii_0 < 20; ++ii_0)
        for (int ii_1 =3D 0; ii_1 < 10; ++ii_1)
            var_17 =3D min(var_6 ? var_8 >> (var_13 - 518868145U) : var_7,
1887837879 || 0);
}
int main() {
    test(2062689408U);
    hash(&seed, var_17);
    printf("%d\n", seed);
    return 0;
}

> $ /usr/gcc-trunk/bin/gcc -O0 bug.c; ./a.out
> 1
> $ /usr/gcc-trunk/bin/gcc -O2 bug.c; ./a.out
> 3

When compiled with -O2 or -O3, it prints 3 instead of 1. Earlier GCCs do not
have this bug.

> $ /usr/gcc-trunk/bin/gcc --version
gcc (GCC) 14.0.0 20230619 (experimental) [master r14-1917-gf8e0270272]
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=