[RFC] ordered comparison of pointer with integer zero warning in Wextra

["Manuel LÃpez-IbÃÃez" <lopezibanez at gmail dot com>]

Dear all,

Currently Wextra warns about a pointer compared against integer zero
with <, <=, >, or >=. This warning is not available in C++ (the
documentation does not say this) and it is implemented in
gcc/c-typeck.c (build_binary_op) in this manner:

     else if (code0 == POINTER_TYPE && null_pointer_constant_p (orig_op1))
	{
	  result_type = type0;
	  if (pedantic || extra_warnings)
	    pedwarn ("ordered comparison of pointer with integer zero");
	}
     else if (code1 == POINTER_TYPE && null_pointer_constant_p (orig_op0))
	{
	  result_type = type1;
	  if (pedantic)
	    pedwarn ("ordered comparison of pointer with integer zero");
	}

That is, given int *p and -Wextra, the above code warns for p < 0 but
not for 0 > p. Given -pedantic, we warn for both situations. This is
also the only warning activated by both pedantic and -Wextra.

Taking into account the above, is there a reason for this? For me, the
best would be to NOT enable the warning for Wextra, so I don't need to
come up with a name for this warning flag. Otherwise, we would have to
document that the warning is enabled by both pedantic and Wextra, so a
user won't be surprised when the warning does not go away by using the
Wno-* form just because pedantic is enabled.

Please, I would appreciate your comments on this, so I can submit a
patch implementing whichever is thought to be the best approach.

Cheers,

Manuel.