[Bug bootstrap/82939] genmatch fills up terminal with endless printing of periods

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82939

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
Unreliable testcase ("works" for me at -O2 but not -O0 -- we need the
default-constructed assignment RHS on the stack to have an uninitialized value
of non-zero):

struct line_maps {
    ~line_maps ();
    bool trace_includes;
};
line_maps::~line_maps () {}
int main ()
{
  line_maps m;
  m.trace_includes = true;
  m = line_maps ();
  if (m.trace_includes)
    return 1;
  return 0;
}

at -O2 gcc 4.2.3 optimizes this to just

main:
.LFB5:
        movzbl  %al, %eax
        ret

...