`this == nullptr` results in undefined behavior

[ShortDevelopment]

Issue

‘this’ pointer cannot be null in well-defined C++ code; pointer may be assumed to always convert to true

Tasks

• Add compiler warning
  clang: -Wundefined-bool-conversion
  msvc: ??
• ImmutableList undefined behavior #6847
• IR.cpp
• Find further places where this may happen

[ppenzin]

This warning should now be enabled in Clang by default, though didn't catch this earlier due to -Werror, I suspect it wasn't enabled in the version from the package manager.

[ShortDevelopment]

ChakraCore/lib/Backend/IR.cpp

Line 4852 in 2af598f

if (this == NULL)

[rhuanjl]

I had a look IR.cpp and the invalid check is being done part of a Debug only feature; so it's not as critical a concern as ImmutableList.

I've also done a sequence of searches in the codebase and I don't think there's anything else.