this-pointer NULL-checks in hotspot codebase [-Wtautological-undefined-compare]

[Florian Weimer]

* Matthias Baesken:

> Do you think the NULL-checks can be removed or is there still some
> value in doing them ?

I believe you need to build OpenJDK in a mode where the compiler assumes
that the this pointer can be null:

  # These flags are required for GCC 6 builds as undefined behaviour in
  # OpenJDK code runs afoul of the more aggressive versions of these
  # optimisations.  Notably, value range propagation now assumes that
  # the this pointer of C++ member functions is non-null.

Thanks,
Florian