[hramrach]

I believe it completely solves the question

? May we remove '*p = 0;', whether we remove the malloc+free or not?

Sure, it does not solve the question when arbitrarily removing NULL pointer checks is OK.

It is true that when the compiler is inlining code or expanding a macro it may have a NULL check that is spurious in environments that do not map page 0 based on the observation that the pointer was dereferenced previously.

And this assumption is incorrect in environments that do map page 0 causing wrong code generation.