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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/110532] New: [14 Regression] Different
 results between -O0 and -O1
Date: Mon, 03 Jul 2023 11:17:24 +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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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110532

            Bug ID: 110532
           Summary: [14 Regression] Different results between -O0 and -O1
           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: ---

Compiler Explorer: https://godbolt.org/z/xE1K6zKbs

The following code snippet:

#include <stdio.h>
unsigned char res, a[25], b[25];
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))
int main() {
    for (int i =3D 0; i < 25; ++i)
        a[i] =3D 116, b[i] =3D 213;
    res =3D (unsigned char)min(b[0] ? (_Bool)-11818 : a[2], max(b[2], 1));
    printf("%d\n", res);
}

> $ /usr/gcc-trunk/bin/gcc -O0 bug.c; ./a.out
> 1
> $ /usr/gcc-trunk/bin/gcc -O1 bug.c; ./a.out
> 213
> $ /usr/gcc-trunk/bin/gcc -O2 bug.c; ./a.out
> 1
> $ /usr/gcc-trunk/bin/gcc -O3 bug.c; ./a.out
> 1
> $ /usr/gcc-trunk/bin/gcc -Os bug.c; ./a.out
> 1
When compiled with -O1, it prints the wrong result 213 instead of 1. 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 20230703 (experimental) [master r14-2244-g1ebf37ece3] (G=
CC)=