C++ PATCH for c++/91844 - Implement CWG 2352, Similar types and reference binding.
Marek Polacek
polacek@redhat.com
Sun Sep 22 19:23:00 GMT 2019
I came across this DR while looking into P0388R4 and realized I need to implement
it before tackling P0388R4. DR 2352 changes the definitions of reference-related
(so that it uses "similar type" instead of "same type") and of reference-compatible
(use a standard conversion sequence), and then P0388R4 further adjusts the
definition of what a "similar type" is.
We have same_type_p but unfortunately we didn't have similar_type_p so I added
that; I made use of comp_cv_qual_signature there.
That means that reference-related is now more broad, which means that we
will be binding more things directly, which has certain consequences, e.g.:
ref-bind1.C is an extended testcase from the DR. We are no longer creating
a temporary, so -Wreturn-local-addr shouldn't trigger.
ref-bind2.C shows that some code is now ill-formed: [dcl.init.ref]p5.4.4
prohibits binding an rvalue reference to an lvalue if T1 is reference-related
to T2, which it now is.
ref-bind3.C shows that some code that has been invalid will become valid:
extending reference-related means avoiding creating a qualification conversion
when binding a parameter here, which changes the ranking. In this case,
it evaded an ambiguity. The comment explains it in more detail.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-09-22 Marek Polacek <polacek@redhat.com>
PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
* call.c (reference_related_p): Use similar_type_p instead of
same_type_p.
(reference_compatible_p): Update implementation to match CWG 2352.
* cp-tree.h (similar_type_p): Declare.
* typeck.c (similar_type_p): New.
* g++.dg/cpp0x/pr33930.C: Add dg-error.
* g++.dg/cpp0x/ref-bind1.C: New test.
* g++.dg/cpp0x/ref-bind2.C: New test.
* g++.dg/cpp0x/ref-bind3.C: New test.
* g++.old-deja/g++.pt/spec35.C: Remove dg-error.
diff --git gcc/cp/call.c gcc/cp/call.c
index 2dad699622e..28b3f332b5d 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -1530,9 +1530,8 @@ reference_related_p (tree t1, tree t2)
/* [dcl.init.ref]
Given types "cv1 T1" and "cv2 T2," "cv1 T1" is reference-related
- to "cv2 T2" if T1 is the same type as T2, or T1 is a base class
- of T2. */
- return (same_type_p (t1, t2)
+ to "cv2 T2" if T1 is similar to T2, or T1 is a base class of T2. */
+ return (similar_type_p (t1, t2)
|| (CLASS_TYPE_P (t1) && CLASS_TYPE_P (t2)
&& DERIVED_FROM_P (t1, t2)));
}
@@ -1545,14 +1544,15 @@ reference_compatible_p (tree t1, tree t2)
/* [dcl.init.ref]
"cv1 T1" is reference compatible with "cv2 T2" if
- * T1 is reference-related to T2 or
- * T2 is "noexcept function" and T1 is "function", where the
- function types are otherwise the same,
- and cv1 is the same cv-qualification as, or greater cv-qualification
- than, cv2. */
- return ((reference_related_p (t1, t2)
- || fnptr_conv_p (t1, t2))
- && at_least_as_qualified_p (t1, t2));
+ a prvalue of type "pointer to cv2 T2" can be converted to the type
+ "pointer to cv1 T1" via a standard conversion sequence. */
+ tree ptype1 = build_pointer_type (t1);
+ tree ptype2 = build_pointer_type (t2);
+ conversion *conv = standard_conversion (ptype1, ptype2, NULL_TREE,
+ /*c_cast_p=*/false, 0, tf_none);
+ if (!conv || conv->bad_p)
+ return false;
+ return true;
}
/* A reference of the indicated TYPE is being bound directly to the
diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
index 6d217fc27a2..9c0f3949c68 100644
--- gcc/cp/cp-tree.h
+++ gcc/cp/cp-tree.h
@@ -7361,6 +7361,7 @@ enum { ce_derived, ce_type, ce_normal, ce_exact };
extern bool comp_except_specs (const_tree, const_tree, int);
extern bool comptypes (tree, tree, int);
extern bool same_type_ignoring_top_level_qualifiers_p (tree, tree);
+extern bool similar_type_p (tree, tree);
extern bool compparms (const_tree, const_tree);
extern int comp_cv_qualification (const_tree, const_tree);
extern int comp_cv_qualification (int, int);
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index d85e5474df2..2c99efb0b03 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -1530,6 +1530,38 @@ same_type_ignoring_top_level_qualifiers_p (tree type1, tree type2)
return same_type_p (type1, type2);
}
+/* Returns nonzero iff TYPE1 and TYPE2 are similar, as per [conv.qual]. */
+
+bool
+similar_type_p (tree type1, tree type2)
+{
+ if (type1 == error_mark_node || type2 == error_mark_node)
+ return false;
+
+ /* Informally, two types are similar if, ignoring top-level cv-qualification:
+ * they are the same type; or
+ * they are both pointers, and the pointed-to types are similar; or
+ * they are both pointers to member of the same class, and the types of
+ the pointed-to members are similar; or
+ * they are both arrays of the same size or both arrays of unknown bound,
+ and the array element types are similar. */
+
+ if (same_type_ignoring_top_level_qualifiers_p (type1, type2))
+ return true;
+
+ if ((TREE_CODE (type1) == POINTER_TYPE && TREE_CODE (type2) == POINTER_TYPE)
+ || (TYPE_PTRDATAMEM_P (type1) && TYPE_PTRDATAMEM_P (type2))
+ || (TREE_CODE (type1) == ARRAY_TYPE && TREE_CODE (type2) == ARRAY_TYPE))
+ {
+ int result = comp_cv_qual_signature (TREE_TYPE (type1),
+ TREE_TYPE (type2));
+ if (result != 0)
+ return true;
+ }
+
+ return false;
+}
+
/* Returns 1 if TYPE1 is at least as qualified as TYPE2. */
bool
diff --git gcc/testsuite/g++.dg/cpp0x/pr33930.C gcc/testsuite/g++.dg/cpp0x/pr33930.C
index 8d9312c019b..ba5b4b943c8 100644
--- gcc/testsuite/g++.dg/cpp0x/pr33930.C
+++ gcc/testsuite/g++.dg/cpp0x/pr33930.C
@@ -6,5 +6,5 @@ int& foo( type&& ggg );
void bar( int* someptr )
{
- int& x = foo( someptr );
+ int& x = foo( someptr ); // { dg-error "cannot bind non-const lvalue reference" }
}
diff --git gcc/testsuite/g++.dg/cpp0x/ref-bind1.C gcc/testsuite/g++.dg/cpp0x/ref-bind1.C
new file mode 100644
index 00000000000..841ec1dc7a0
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/ref-bind1.C
@@ -0,0 +1,36 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+// These should bind directly to ptr, so no -Wreturn-local-addr warnings.
+int *ptr;
+
+const int *const &
+fn1 ()
+{
+ return ptr;
+}
+
+int **const ptr2 = nullptr;
+const int *const *const &
+fn2 ()
+{
+ return ptr2;
+}
+
+int (*ptr3)[10];
+using T = const int (*const)[10];
+
+T&
+fn3 ()
+{
+ return ptr3;
+}
+
+int (**ptr4)[5] = nullptr;
+using T2 = const int (*const *const)[5];
+
+T2&
+fn4 ()
+{
+ return ptr4;
+}
diff --git gcc/testsuite/g++.dg/cpp0x/ref-bind2.C gcc/testsuite/g++.dg/cpp0x/ref-bind2.C
new file mode 100644
index 00000000000..967c59e06fd
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/ref-bind2.C
@@ -0,0 +1,15 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+// "const int *" and "int *" are reference-related, and 5.4.4.
+// says that in that case, if the reference is an rvalue reference,
+// the initializer expression shall not be an lvalue.
+
+int &f (const int *&&);
+
+void
+fn (int *p)
+{
+ const int *&&r = p; // { dg-error "cannot bind rvalue reference" }
+ f (p); // { dg-error "cannot bind rvalue reference" }
+}
diff --git gcc/testsuite/g++.dg/cpp0x/ref-bind3.C gcc/testsuite/g++.dg/cpp0x/ref-bind3.C
new file mode 100644
index 00000000000..16e1bfe6ccc
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/ref-bind3.C
@@ -0,0 +1,22 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+template<typename T> int f (const T *const &); // (1)
+template<typename T> int f (T *const &); // (2)
+template<typename T> int f (T *); // (3)
+
+/* Before CWG 2352, (2) was a better match than (1), but (2) and (3) were
+ equally good, so there was an ambiguity. (2) was better than (1) because
+ (1) required a qualification conversion whereas (2) didn't. But with this
+ CWG, (1) no longer requires a qualification conversion, because the types
+ "const int* const" and "int *" are now considered reference-related and we
+ bind directly, and (1) is more specialized than (2). And (1) is also a
+ better match than (3). */
+
+void
+g (int *p, const int *q, const int *const r)
+{
+ f (p); // calls (1)
+ f (q); // calls (1)
+ f (r); // calls (1)
+}
diff --git gcc/testsuite/g++.old-deja/g++.pt/spec35.C gcc/testsuite/g++.old-deja/g++.pt/spec35.C
index 581bb8ed537..93e953df7e7 100644
--- gcc/testsuite/g++.old-deja/g++.pt/spec35.C
+++ gcc/testsuite/g++.old-deja/g++.pt/spec35.C
@@ -14,9 +14,9 @@ template <typename T> int Foo (T &); // { dg-message "note" } candidate
template <typename T> int Qux (T); // { dg-message "note" }
template <typename T> int Qux (T const &); // { dg-message "note" } candidate
-template <typename T> int Bar (T const *const &); // { dg-message "note" }
-template <typename T> int Bar (T *const &); // { dg-message "note" } candidate
-template <typename T> int Bar (T *); // { dg-message "note" } candidate
+template <typename T> int Bar (T const *const &);
+template <typename T> int Bar (T *const &);
+template <typename T> int Bar (T *);
template <typename T> int Baz (T *const &); // { dg-message "note" }
template <typename T> int Baz (T *); // { dg-message "note" } candidate
@@ -24,7 +24,7 @@ template <typename T> int Baz (T *); // { dg-message "note" } candi
int Baz (int const *ptr, int *ptr2)
{
Baz (ptr2); // { dg-error "ambiguous" }
- Bar (ptr2); // { dg-error "ambiguous" }
+ Bar (ptr2);
Foo (ptr2); // { dg-error "ambiguous" }
Qux (ptr2); // { dg-error "ambiguous" }
return 0;
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