[C++] Undefined behaviour in exception handling

[haaawk]

There is a potential null pointer dereference here: https://github.com/antlr/antlr3/blob/master/runtime/Cpp/include/antlr3exception.inl#L315

m_expectingSet is very often null. It should be checked before doing anything with this pointer.

Currently it leads to undefined behaviour and sometimes crashes of the whole program.

[strfry]

An additional explanation: The bitsetLoad() function tries to work around being called with a NULL this pointer:

antlr3/runtime/Cpp/include/antlr3bitset.inl

Line 54 in 5c2a916

if (this != NULL)

Apparently this still undefined behaviour, and recent GCC versions assume this to be non-null and optimize this check away, with a warning:
include/antlr3cpp/antlr3bitset.inl:54:2: warning: nonnull argument ‘this’ compared to NULL [-Wnonnull-compare]

~~The only workaround I see is probably to manually change every line where bitsetLoad() might be called with a NULL pointer. ~~

The GCC 6 Release Notes describe this issue as a consequence of Value range propagation, -fno-delete-null-pointer-checks can be used as a compiler flag to keep the old code working.