[Bug target/77826] New: [7 Regression] ICE in decompose, at wide-int.h:928 w/ -m64 -O2 and above

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77826

            Bug ID: 77826
           Summary: [7 Regression] ICE in decompose, at wide-int.h:928 w/
                    -m64 -O2 and above
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu
             Build: x86_64-pc-linux-gnu

At least gcc-7.0.0-alpha20160925 and gcc-7.0.0-alpha20161002 ICE when compiling
the following reduced snippet at -O2 (-Os, -O2, -Ofast):

void
fi(unsigned long int *v0, unsigned int ow, int q2)
{
  if (ow + q2 != 0)
    if (q2 == 1)
    {
      *v0 |= q2;
      q2 ^= *v0;
    }
}

% x86_64-pc-linux-gnu-gcc-7.0.0-alpha20161002 -O2 -c cj0mr0fp.c
cj0mr0fp.c: In function 'fi':
cj0mr0fp.c:10:1: internal compiler error: in decompose, at wide-int.h:928
 }
 ^

I cannot reproduce it w/ -m32, or w/ the same snapshot targeted against 32-bit
BE powerpc.