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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/110494] New: [14 Regression] Wrong code at
 -O3 on x86_64-pc-linux-gnu
Date: Fri, 30 Jun 2023 05:12:15 +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-Who: jwzeng at nuaa dot edu.cn
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110494

            Bug ID: 110494
           Summary: [14 Regression] Wrong code at -O3 on
                    x86_64-pc-linux-gnu
           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: ---

Link to the Compiler Explorer: https://godbolt.org/z/dq38c9zea

The following code snippet:

#include <stdio.h>
unsigned long long int seed =3D 0;
unsigned int var_1 =3D 631366671U;
#define min(a, b) ((a) < (b) ? (a) : (b))
int main() {
    short a[18];
    int b =3D 1;
    unsigned long long int c[18];
    unsigned long long int d[18];
    for (int i =3D 0; i < 18; ++i)
        a[i] =3D 4, c[i] =3D 3, d[i] =3D 2;
    for (unsigned short i =3D 1; i < 16; i +=3D var_1 - 57737)
        a[i] =3D (short)min(b % (~var_1), c[i] ? d[i] : (long long unsigned
int)b);
    for (int i =3D 0; i < 18; ++i)
        seed ^=3D a[i];
    printf("%llu\n", seed);
}

> $ /usr/gcc-trunk/bin/gcc -O0 bug.c; ./a.out
> 5
> $ /usr/gcc-trunk/bin/gcc -O1 bug.c; ./a.out
> 5
> $ /usr/gcc-trunk/bin/gcc -O2 bug.c; ./a.out
> 5
> $ /usr/gcc-trunk/bin/gcc -O3 bug.c; ./a.out
> 7
> $ /usr/gcc-trunk/bin/gcc -Os bug.c; ./a.out
> 5
When compiled with -O3, it prints the wrong result 7 instead of 5. Earlier =
GCCs
do not have this bug.

> $ /usr/gcc-trunk/bin/gcc --version
Using built-in specs.
COLLECT_GCC=3D/home/compilers/gcc/gcc-trunk/bin/gcc
COLLECT_LTO_WRAPPER=3D/home/compilers/gcc/gcc-trunk/bin/../libexec/gcc/x86_=
64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk-source/gcc/configure
--enable-languages=3Dc,c++,fortran --enable-checking=3Drelease
--enable-valgrind-annotations --disable-werror --disable-libstdcxx-pch
--enable-libgomp --enable-lto --enable-gold --with-plugin-ld=3Dgold
--prefix=3D/usr/local/gcc-trunk
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230619 (experimental) [master r14-1917-gf8e0270272] (G=
CC)=