Patch Set 1:
all checks of (this == null) will be eliminated by GCC >= 6.1 (https://gcc.gnu.org/gcc-6/changes.html, Value range propagation now assumes that the this pointer of C++ member functions is non-null. This eliminates common null pointer checks but also breaks some non-conforming code-bases (such as Qt-5, Chromium, KDevelop). As a temporary work-around -fno-delete-null-pointer-checks can be used. Wrong code can be identified by using -fsanitize=undefined.)
But given the "make check" failure we seem to expect that. You will need to move the null check before calling the function or create a method wrapper where the tbf pointer is passed so we can do the null check there.
thanks for the explanation. this is also the reason, why make check fails on my laptop. gcc --version gcc (GCC) 6.1.1 20160501