[Bug rtl-optimization/81063] New: wrong code at -O1 and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81063

            Bug ID: 81063
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

This appears to be a very recent regression. 

$ 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 20170611 (experimental) [trunk revision 249105] (GCC) 
$ 
$ gcc-trunk -O0 small.c; ./a.out
$ 
$ gcc-trunk -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 


---------------------------------


struct A
{
  int b;
  int c:2;
};

struct B
{
  int e;
  struct A f;
} g = {0, {0, 1}}, j;

struct A *h = &g.f;

int main ()
{
  struct A k;
  struct B l = j, i = l;
  if (!i.f.b)
    k = i.f;
  *h = k;
  if (g.f.c != 0) 
    __builtin_abort (); 
  return 0; 
}