return true;
}
+/* Return true if a class CTYPE is either std::reference_wrapper or
+ std::ref_view, or a reference wrapper class. We consider a class
+ a reference wrapper class if it has a reference member and a
+ constructor taking the same reference type. */
+
+static bool
+reference_like_class_p (tree ctype)
+{
+ if (!CLASS_TYPE_P (ctype))
+ return false;
+
+ /* Also accept a std::pair<const T&, const T&>. */
+ if (std_pair_ref_ref_p (ctype))
+ return true;
+
+ tree tdecl = TYPE_NAME (TYPE_MAIN_VARIANT (ctype));
+ if (decl_in_std_namespace_p (tdecl))
+ {
+ tree name = DECL_NAME (tdecl);
+ return (name
+ && (id_equal (name, "reference_wrapper")
+ || id_equal (name, "ref_view")));
+ }
+ for (tree fields = TYPE_FIELDS (ctype);
+ fields;
+ fields = DECL_CHAIN (fields))
+ {
+ if (TREE_CODE (fields) != FIELD_DECL || DECL_ARTIFICIAL (fields))
+ continue;
+ tree type = TREE_TYPE (fields);
+ if (!TYPE_REF_P (type))
+ continue;
+ /* OK, the field is a reference member. Do we have a constructor
+ taking its type? */
+ for (tree fn : ovl_range (CLASSTYPE_CONSTRUCTORS (ctype)))
+ {
+ tree args = FUNCTION_FIRST_USER_PARMTYPE (fn);
+ if (args
+ && same_type_p (TREE_VALUE (args), type)
+ && TREE_CHAIN (args) == void_list_node)
+ return true;
+ }
+ }
+ return false;
+}
+
/* Helper for maybe_warn_dangling_reference to find a problematic CALL_EXPR
that initializes the LHS (and at least one of its arguments represents
a temporary, as outlined in maybe_warn_dangling_reference), or NULL_TREE
const int& y = (f(1), 42); // NULL_TREE
const int& z = f(f(1)); // f(f(1))
- EXPR is the initializer. */
+ EXPR is the initializer. If ARG_P is true, we're processing an argument
+ to a function; the point is to distinguish between, for example,
+
+ Ref::inner (&TARGET_EXPR <D.2839, F::foo (fm)>)
+
+ where we shouldn't warn, and
+
+ Ref::inner (&TARGET_EXPR <D.2908, F::foo (&TARGET_EXPR <...>)>)
+
+ where we should warn (Ref is a reference_like_class_p so we see through
+ it. */
static tree
-do_warn_dangling_reference (tree expr)
+do_warn_dangling_reference (tree expr, bool arg_p)
{
STRIP_NOPS (expr);
+
+ if (arg_p && expr_represents_temporary_p (expr))
+ {
+ /* An attempt to reduce the number of -Wdangling-reference
+ false positives concerning reference wrappers (c++/107532).
+ When we encounter a reference_like_class_p, we don't warn
+ just yet; instead, we keep recursing to see if there were
+ any temporaries behind the reference-wrapper class. */
+ tree e = expr;
+ while (handled_component_p (e))
+ e = TREE_OPERAND (e, 0);
+ if (!reference_like_class_p (TREE_TYPE (e)))
+ return expr;
+ }
+
switch (TREE_CODE (expr))
{
case CALL_EXPR:
std::pair<const int&, const int&> v = std::minmax(1, 2);
which also creates a dangling reference, because std::minmax
returns std::pair<const T&, const T&>(b, a). */
- if (!(TYPE_REF_OBJ_P (rettype) || std_pair_ref_ref_p (rettype)))
+ if (!(TYPE_REF_OBJ_P (rettype) || reference_like_class_p (rettype)))
return NULL_TREE;
/* Here we're looking to see if any of the arguments is a temporary
if (!DECL_NONSTATIC_MEMBER_FUNCTION_P (fndecl)
&& !TYPE_REF_P (TREE_TYPE (arg)))
continue;
- /* It could also be another call taking a temporary and returning
- it and initializing this reference parameter. */
- if (do_warn_dangling_reference (arg))
- return expr;
STRIP_NOPS (arg);
if (TREE_CODE (arg) == ADDR_EXPR)
arg = TREE_OPERAND (arg, 0);
- if (expr_represents_temporary_p (arg))
+ /* Recurse to see if the argument is a temporary. It could also
+ be another call taking a temporary and returning it and
+ initializing this reference parameter. */
+ if (do_warn_dangling_reference (arg, /*arg_p=*/true))
return expr;
/* Don't warn about member function like:
std::any a(...);
return NULL_TREE;
}
case COMPOUND_EXPR:
- return do_warn_dangling_reference (TREE_OPERAND (expr, 1));
+ return do_warn_dangling_reference (TREE_OPERAND (expr, 1), arg_p);
case COND_EXPR:
- if (tree t = do_warn_dangling_reference (TREE_OPERAND (expr, 1)))
+ if (tree t = do_warn_dangling_reference (TREE_OPERAND (expr, 1), arg_p))
return t;
- return do_warn_dangling_reference (TREE_OPERAND (expr, 2));
+ return do_warn_dangling_reference (TREE_OPERAND (expr, 2), arg_p);
case PAREN_EXPR:
- return do_warn_dangling_reference (TREE_OPERAND (expr, 0));
+ return do_warn_dangling_reference (TREE_OPERAND (expr, 0), arg_p);
case TARGET_EXPR:
- return do_warn_dangling_reference (TARGET_EXPR_INITIAL (expr));
+ return do_warn_dangling_reference (TARGET_EXPR_INITIAL (expr), arg_p);
default:
return NULL_TREE;
}
= make_temp_override (global_dc->dc_warn_system_headers,
(!in_system_header_at (DECL_SOURCE_LOCATION (decl))
|| global_dc->dc_warn_system_headers));
- if (tree call = do_warn_dangling_reference (init))
+ if (tree call = do_warn_dangling_reference (init, /*arg_p=*/false))
{
auto_diagnostic_group d;
if (warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wdangling_reference,
--- /dev/null
+// PR c++/107532
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wdangling-reference" }
+
+struct Plane { unsigned int bytesused; };
+
+// Passes a reference through. Does not change lifetime.
+template <typename T>
+struct Ref {
+ const T& i_;
+ Ref(const T & i) : i_(i) {}
+ const T & inner();
+};
+
+struct FrameMetadata {
+ Ref<const Plane> planes() const { return p_; }
+
+ Plane p_;
+};
+
+void bar(const Plane & meta);
+void foo(const FrameMetadata & fm)
+{
+ const Plane & meta = fm.planes().inner();
+ bar(meta);
+ const Plane & meta2 = FrameMetadata().planes().inner(); // { dg-warning "dangling reference" }
+ bar(meta2);
+}
+
+struct S {
+ const S& self () { return *this; }
+} s;
+
+const S& r1 = s.self();
+const S& r2 = S().self(); // { dg-warning "dangling reference" }
+
+struct D {
+};
+
+struct C {
+ D d;
+ Ref<const D> get() const { return d; }
+};
+
+struct B {
+ C c;
+ const C& get() const { return c; }
+ B();
+};
+
+struct A {
+ B b;
+ const B& get() const { return b; }
+};
+
+void
+g (const A& a)
+{
+ const auto& d1 = a.get().get().get().inner();
+ (void) d1;
+ const auto& d2 = A().get().get().get().inner(); // { dg-warning "dangling reference" }
+ (void) d2;
+ const auto& d3 = A().b.get().get().inner(); // { dg-warning "dangling reference" }
+ (void) d3;
+ const auto& d4 = a.b.get().get().inner();
+ (void) d4;
+ const auto& d5 = a.b.c.get().inner();
+ (void) d5;
+ const auto& d6 = A().b.c.get().inner(); // { dg-warning "dangling reference" }
+ (void) d6;
+ Plane p;
+ Ref<Plane> r(p);
+ const auto& d7 = r.inner();
+ (void) d7;
+ const auto& d8 = Ref<Plane>(p).inner();
+ (void) d8;
+}