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Re: [C++ PATCH] For -Wformat purposes use ellipsis args before class to pointer to class conversion (PR c++/84076)
On Fri, Mar 09, 2018 at 11:28:47AM -0500, Jason Merrill wrote:
> On Thu, Mar 8, 2018 at 4:26 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> > On Thu, Mar 08, 2018 at 04:20:40PM -0500, Jason Merrill wrote:
> >> On Thu, Mar 8, 2018 at 1:08 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> >> > The reporter complains that -Wformat incorrectly reports std::string* passed
> >> > to "%s" format rather than std::string, which is what the user did.
> >> >
> >> > This transformation of non-trivial copy init or dtor classes in ellipsis is
> >> > done by convert_arg_to_ellipsis; that function does many changes and all
> >> > but this one look desirable for the -Wnonnull/-Wformat/-Wsentinel/-Wrestrict
> >> > warnings. We prepare a special argument vector in any case, so this patch
> >> > just arranges to undo what convert_arg_to_ellipsis did for the classes.
> >> > I think -Wnonnull shouldn't care, because when passing such a class by
> >> > value, it will be non-NULL (and -Wnonnull looks only for literal NULLs
> >> > anyway), -Wrestrict only cares about named arguments and -Wsentinel only
> >> > cares about NULL arguments passed to ellipsis.
> >>
> >> I notice that convert_arg_to_ellipsis generates a pointer-typed
> >> expression, whereas convert_for_arg_passing generates a reference.
> >> Does correcting that inconsistency help?
> >
> > No (though I think it is a good idea anyway).
>
> Perhaps then check_format_types could look through REFERENCE_TYPE,
> since there are no actual expressions of reference type.
It can be done in the caller as well like below, or in c-format.c's
if (warn_format)
{
/* FIXME: Rewrite all the internal functions in this file
to use the ARGARRAY directly instead of constructing this
temporary list. */
tree params = NULL_TREE;
int i;
for (i = nargs - 1; i >= 0; i--)
params = tree_cons (NULL_TREE, argarray[i], params);
check_format_info (&info, params, arglocs);
}
I'm afraid the c-format.c has so many uses of the params list that it is
hard to tweak it anywhere else.
2018-03-09 Jason Merrill <jason@redhat.com>
Jakub Jelinek <jakub@redhat.com>
PR c++/84076
* call.c (convert_arg_to_ellipsis): Instead of cp_build_addr_expr
build ADDR_EXPR with REFERENCE_TYPE.
(build_over_call): For purposes of check_function_arguments, if
argarray[j] is ADDR_EXPR with REFERENCE_TYPE created above, use
its operand rather than the argument itself.
* g++.dg/warn/Wformat-2.C: New test.
--- gcc/cp/call.c.jj 2018-03-09 09:01:32.017423737 +0100
+++ gcc/cp/call.c 2018-03-09 18:12:34.973494714 +0100
@@ -7209,7 +7209,7 @@ convert_arg_to_ellipsis (tree arg, tsubs
"passing objects of non-trivially-copyable "
"type %q#T through %<...%> is conditionally supported",
arg_type);
- return cp_build_addr_expr (arg, complain);
+ return build1 (ADDR_EXPR, build_reference_type (arg_type), arg);
}
/* Build up a real lvalue-to-rvalue conversion in case the
copy constructor is trivial but not callable. */
@@ -8018,7 +8018,15 @@ build_over_call (struct z_candidate *can
tree *fargs = (!nargs ? argarray
: (tree *) alloca (nargs * sizeof (tree)));
for (j = 0; j < nargs; j++)
- fargs[j] = maybe_constant_value (argarray[j]);
+ {
+ /* For -Wformat undo the implicit passing by hidden reference
+ done by convert_arg_to_ellipsis. */
+ if (TREE_CODE (argarray[j]) == ADDR_EXPR
+ && TREE_CODE (TREE_TYPE (argarray[j])) == REFERENCE_TYPE)
+ fargs[j] = TREE_OPERAND (argarray[j], 0);
+ else
+ fargs[j] = maybe_constant_value (argarray[j]);
+ }
warned_p = check_function_arguments (input_location, fn, TREE_TYPE (fn),
nargs, fargs, NULL);
--- gcc/testsuite/g++.dg/warn/Wformat-2.C.jj 2018-03-09 17:59:57.098113181 +0100
+++ gcc/testsuite/g++.dg/warn/Wformat-2.C 2018-03-09 17:59:57.098113181 +0100
@@ -0,0 +1,17 @@
+// PR c++/84076
+// { dg-do compile }
+// { dg-options "-Wformat" }
+
+struct S { ~S (); };
+struct T { T (); T (const T &); };
+
+void
+foo ()
+{
+ S s;
+ T t;
+ __builtin_printf ("%s\n", s); // { dg-warning "format '%s' expects argument of type 'char\\*', but argument 2 has type 'S'" }
+ __builtin_printf ("%s\n", t); // { dg-warning "format '%s' expects argument of type 'char\\*', but argument 2 has type 'T'" }
+ __builtin_printf ("%s\n", &s);// { dg-warning "format '%s' expects argument of type 'char\\*', but argument 2 has type 'S\\*'" }
+ __builtin_printf ("%s\n", &t);// { dg-warning "format '%s' expects argument of type 'char\\*', but argument 2 has type 'T\\*'" }
+}
Jakub