https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97520
--- Comment #5 from suochenyao at 163 dot com <suochenyao at 163 dot com> ---
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I think this can be reproduced with "-fno-strict-aliasing"...
I am not sure whether it can be helpful...
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OS and Platform:
CentOS Linux release 7.8.2003 (Core), x86_64 GNU/Linux
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Program:
int printf(const char *, ...);
union {
long a;
int b;
} c;
int d=0;
long e=0;
long *f = &c.a;
short g=0;
int *h = &c.b;
short i(int j) {
g = *h;
*f = 3;
for (;; e--) {
if (*h)
return d;
*h = j;
}
return 0;
}
int main() {
i(1);
printf("%d\n", (int)e);
return 0;
}
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gcc version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=/home/suocy/bin/gcc-dev/bin/gcc
COLLECT_LTO_WRAPPER=/home/suocy/bin/gcc-dev/libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/home/suocy/bin/gcc-dev/
--disable-multilib --enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.0.0 20201029 (experimental) (GCC)
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Command Lines:
$ gcc a.c -o a.o1
$ gcc -Wall -Wextra -fno-strict-aliasing -fwrapv -Og -fgcse -fstrict-aliasing
a.c -o a.o2
$ gcc -Og -fgcse -fstrict-aliasing a.c -o a.o3
$ ./a.o1
0
$ ./a.o2
-1
$ ./a.o3
-1
