[Bug ipa/63745] [4.9/5 Regression] mythtv build failure due to aggressive speculative devirtualization

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63745

--- Comment #3 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
And here's a hopefully valid testcase:

markus@x4 tmp % cat main.ii

struct VideoBuffers
{
  void StartDisplayingFrame ();
};
struct B
{
  VideoBuffers vbuffers;
  virtual void
  StartDisplay ()
  {
    vbuffers.StartDisplayingFrame ();
  }
};
struct VideoPerformanceTest
{
  B *Test_vo;
  void
  Test ()
  {
    if (!Test_vo)
      return;
    while (1)
      Test_vo->StartDisplay ();
  }
};

VideoPerformanceTest a;
int
main () { a.Test (); }