[Bug tree-optimization/101062] New: wrong code with "-O2 -fno-toplevel-reorder -frename-registers"

["suochenyao at 163 dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101062

            Bug ID: 101062
           Summary: wrong code with "-O2 -fno-toplevel-reorder
                    -frename-registers"
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: suochenyao at 163 dot com
  Target Milestone: ---

*******************************************************************************
OS and Platform:
CentOS Linux release 7.8.2003 (Core), x86_64 GNU/Linux
*******************************************************************************
Program:
int printf(const char *, ...);
union a {
  signed b : 5;
};
int c;
volatile union a d[7] = {{8}};
short e = 1;
void f() {
  c = 5;
  for (; c; c--) {
    short *g = &e;
    *g = d[6].b = 0;
  }
}
int main() {
  f();
  printf("%d\n", e);
}
*******************************************************************************
gcc version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=/data/bin/gcc-dev/bin/gcc
COLLECT_LTO_WRAPPER=/data/bin/gcc-dev/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/data/bin/gcc-dev --disable-multilib
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210613 (experimental) (GCC)

git version: 681143b9b94d7f1c88a7c34e2250865c31191959
*******************************************************************************
Command Lines:
$ gcc a.c -o a1.out
$ gcc -O2 -fno-toplevel-reorder -frename-registers -Wall -Wextra
-fno-strict-aliasing -fwrapv a.c -o a2.out
$ ./a1.out
0
$ ./a2.out
1