On Mon, Jan 09, 2017 at 12:18:01PM +0100, Jakub Jelinek wrote:
> On Mon, Jan 09, 2017 at 10:21:47AM +0100, Marek Polacek wrote:
> > +/* Callback function to determine whether an expression TP or one of its
> > + subexpressions comes from macro expansion. Used to suppress bogus
> > + warnings. */
> > +
> > +static tree
> > +expr_from_macro_expansion_r (tree *tp, int *, void *)
> > +{
> > + if (CAN_HAVE_LOCATION_P (*tp)
> > + && from_macro_expansion_at (EXPR_LOCATION (*tp)))
> > + return integer_zero_node;
> > +
> > + return NULL_TREE;
> > +}
>
> I know this is hard issue, but won't it disable the warning way too often?
>
> Perhaps it is good enough for the initial version (GCC 7), but doesn't it stop
> whenever one uses NULL in the branches, or some other trivial macros like
> that? Perhaps we want to do the analysis if there is anything from macro
> expansion side-by-side on both the expressions and if you find something
> from a macro expansion, then still warn if both corresponding expressions
> are from the same macro expansion (either only non-function like one, or
> perhaps also function-like one with the same arguments, if it is possible
> to figure out those somehow)? And perhaps it would be nice to choose
> warning level, whether you want to warn only under these rules (no macros
> or something smarter if implemented) vs. some certainly non-default more
> aggressive mode that will just warn no matter what macros there are.
I agree that not warning for
if (foo)
return NULL;
else
return NULL;
is bad. But how can I compare those expressions side-by-side? I'm not finding
anything. :(
As for the idea of multiple levels, sure, I could do that, although I'd prefer
to get the initial version in first.
Marek
