Operator == takes references and those can never be 0 according to the standard.

So the code "if (!!&a != !!&b) return false;" (and similar), which was apparently meant to handle null referrences, is going to get optimized out.

The introduction of null referrences by calling operator == on dereferenced pointers is actually undefined behavior.

The clang compiler also warns about this issue:

.../src/shared/qbs/src/lib/corelib/language/resolvedfilecontext.cpp:78: warning: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to always convert to true [-Wundefined-bool-conversion]
if (!!&a != !!&b)
~ ^