[Bug c/81740] New: wrong code at -O3 in both 32-bit and 64-bit modes on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81740

            Bug ID: 81740
           Summary: wrong code at -O3 in both 32-bit and 64-bit modes on
                    x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com
  Target Milestone: ---

$ gcc-trunk -v 
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 8.0.0 20170806 (experimental) [trunk revision 250895] (GCC) 
$ 
$ gcc-trunk -O3 small.c ; ./a.out > O3.txt
$ gcc-trunk -O0 small.c ; ./a.out > O0.txt
$ diff O3.txt O0.txt 
37c37
< 0
---
> 4
$ cat small.c
extern int printf(const char *, ...);
int a[8][10];
short b;
int c, i, d;
int main() {
  a[2][5] = b = 4;
  for (; b; b--) {
    c = 0;
    for (; c <= 6; c++)
      a[c + 1][b + 2] = a[c][b + 1];
  }
  for (; i < 8; i++) {
    d = 0;
    for (; d < 10; d++)
      printf("%d\n", a[i][d]);
  }
  return 0;
}
$