first pass at null pointer constants

AFAICS, that should do null pointer constants right.  We assign
special instance of void * (&null_ctype) to (void *)<zero integer
constant expression> and replace it with normal void * when we
don't want null pointer constant.  is_zero_constant() checks if
we have an integer constant expression, does conservative expand
(i.e. instead of generating an error on 1/0, etc. leaves the
node unreplaced) and checks if we have reduced the sucker to
EXPR_VALUE[0] without comma taint.

Implemented all (AFAICS) special cases involving null pointer
constants; most changes in evaluate_compare() and evaluate_conditional().
Both are still incomplete; handling of qualifiers is still missing,
but that's a separate story.

Note that we get two new sets of warnings on the kernel build; one is
due to wrong size_t (handled in the next patch; didn't show up until
now since we didn't warn on comparison of pointers to incompatible
types) and another is a pile of warnings about integer 0 used as NULL
on
	if (p == 0)
where p is a pointer.  Additionally, there's an idiotic
	(p>0)
in one place (again, p is a pointer).  Bugger if I know how gcc doesn't
warn on that one, it's certainly a standard violation and bloody pointless
even as extension...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 1 insertions, 0 deletions

diff --git a/expression.h b/expression.h
index 23ca408..02eec02 100644
--- a/expression.h
+++ b/expression.h
@@ -154,6 +154,7 @@ struct expression {
 };
 
 /* Constant expression values */
+int is_zero_constant(struct expression *);
 long long get_expression_value(struct expression *);
 long long const_expression_value(struct expression *);