[Bug tree-optimization/86886] New: Gcc miscompiles at -O3 on valid code

["helloqirun at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86886

            Bug ID: 86886
           Summary: Gcc miscompiles at -O3 on valid code
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: helloqirun at gmail dot com
  Target Milestone: ---

It also affects gcc-8.1 at -O3. gcc-6.1 works fine.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/home/absozero/trunk/root-gcc/libexec/gcc/x86_64-pc-linux-gnu/9.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --prefix=/home/absozero/trunk/root-gcc
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 9.0.0 20180807 (experimental) [trunk revision 263356] (GCC)



$ gcc-6.1 -O3 abc.c; ./a.out
0

$ gcc abc.c; ./a.out
0

$ gcc-8.1 -O3 abc.c; ./a.out
1

$ gcc-trunk -O3 abc.c; ./a.out
1


$ cat abc.c
void printf();
typedef int f;
short g, k, l, n;
union {
  int b;
  short c;
} h;
f d, e;
unsigned short *i = &h.c;
unsigned short **j = &i;
f *m = &d, *o = &h.b;
void p(f a) {
  *o = 0;
  for (; e;)
    ;
  n = **j;
  l = n;
  unsigned char aq = n;
  k = g == 0 ? aq : 0;
  *m = k;
}
int main() {
  **j = 1;
  p(6);
  printf("%d\n", d);
}