[Bug rtl-optimization/68011] New: wrong code at -O1 and above on x86_64-linux-gnu in 64-bit mode

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68011

            Bug ID: 68011
           Summary: wrong code at -O1 and above on x86_64-linux-gnu in
                    64-bit mode
           Product: gcc
           Version: 6.0
            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: ---

The current gcc trunk mis-compiles the following code on x86_64-linux-gnu at
-O1 and above in the 64-bit mode (but not in the 32-bit mode). 

This is a regression from 5.2.x.


$ 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/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20151018 (experimental) [trunk revision 228953] (GCC) 
$ 
$ gcc-trunk -m64 -O0 small.c; ./a.out
$ gcc-trunk -m32 -O1 small.c; ./a.out
$ gcc-5.2 -m64 -O1 small.c; ./a.out
$ 
$ gcc-trunk -m64 -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


struct S
{
  int f0;
  int f1;
  int f2;
  short f3;
  int f4:1;
} a, c = {0, 0, 1, 0, 0};

int d;

int
main ()
{
  struct S e = c;
  e.f0++;
  d = e.f3;
  a = e;

  if (a.f2 != 1)
    __builtin_abort ();

  return 0;
}