[PATCH v6 10/11] Add rvalue references to overloading resolution

Keith Seitz
2017-03-10T20:14:29Z

This patch introduces changes to rank_one_type() dealing with ranking an rvalue
reference type when selecting a best viable function from a set of candidate
functions. The 4 new added rules for rvalue references are:

1) An rvalue argument cannot be bound to a non-const lvalue reference parameter
and an lvalue argument cannot be bound to an rvalue reference parameter.
[C++11 13.3.3.1.4p3]

2) If a conversion to one type of reference is an identity conversion, and a
conversion to the second type of reference is a non-identity conversion, choose
the first type. [C++11 13.3.3.2p3]

3) An rvalue should be first tried to bind to an rvalue reference, and then to
an lvalue reference. [C++11 13.3.3.2p3]

4) An lvalue reference to a function gets higher priority than an rvalue
reference to a function. [C++11 13.3.3.2p3]

There are no changes to this patch from v5.

NOTE: This patch is not exactly correct. See c++/15372 for tracking overload
resolution bugs.

gdb/ChangeLog

PR gdb/14441
From Artemiy Volkov <artemiyv@acm.org>
* gdbtypes.c (rank_one_type): Implement overloading
resolution rules regarding rvalue references.
---
gdb/ChangeLog | 7 +++++++
gdb/gdbtypes.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ee3de5c..338f412 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -2,6 +2,13 @@

PR gdb/14441
From Artemiy Volkov <artemiyv@acm.org>
+ * gdbtypes.c (rank_one_type): Implement overloading
+ resolution rules regarding rvalue references.
+
+2017-MM-DD Keith Seitz <keiths@redhat.com>
+
+ PR gdb/14441
+ From Artemiy Volkov <artemiyv@acm.org>
* aarch64-tdep.c (aarch64_type_align)
(aarch64_extract_return_value, aarch64_store_return_value): Change
lvalue reference type checks to general reference type checks.
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index defc00d..6f3aeab 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -58,6 +58,8 @@ const struct rank VOID_PTR_CONVERSION_BADNESS = {2,0};
const struct rank BOOL_CONVERSION_BADNESS = {3,0};
const struct rank BASE_CONVERSION_BADNESS = {2,0};
const struct rank REFERENCE_CONVERSION_BADNESS = {2,0};
+const struct rank LVALUE_REFERENCE_TO_RVALUE_BINDING_BADNESS = {5,0};
+const struct rank DIFFERENT_REFERENCE_TYPE_BADNESS = {6,0};
const struct rank NULL_POINTER_CONVERSION_BADNESS = {2,0};
const struct rank NS_POINTER_CONVERSION_BADNESS = {10,0};
const struct rank NS_INTEGER_POINTER_CONVERSION_BADNESS = {3,0};
@@ -3611,15 +3613,65 @@ rank_one_type (struct type *parm, struct type *arg, struct value *value)
{
struct rank rank = {0,0};

- if (types_equal (parm, arg))
- return EXACT_MATCH_BADNESS;
-
/* Resolve typedefs */
if (TYPE_CODE (parm) == TYPE_CODE_TYPEDEF)
parm = check_typedef (parm);
if (TYPE_CODE (arg) == TYPE_CODE_TYPEDEF)
arg = check_typedef (arg);

+ if (value != NULL)
+ {
+ /* An rvalue argument cannot be bound to a non-const lvalue
+ reference parameter... */
+ if (VALUE_LVAL (value) == not_lval
+ && TYPE_CODE (parm) == TYPE_CODE_REF
+ && !TYPE_CONST (parm->main_type->target_type))
+ return INCOMPATIBLE_TYPE_BADNESS;
+
+ /* ... and an lvalue argument cannot be bound to an rvalue
+ reference parameter. [C++ 13.3.3.1.4p3] */
+ if (VALUE_LVAL (value) != not_lval
+ && TYPE_CODE (parm) == TYPE_CODE_RVALUE_REF)
+ return INCOMPATIBLE_TYPE_BADNESS;
+ }
+
+ if (types_equal (parm, arg))
+ return EXACT_MATCH_BADNESS;
+
+ /* An lvalue reference to a function should get higher priority than an
+ rvalue reference to a function. */
+
+ if (value != NULL && TYPE_CODE (arg) == TYPE_CODE_RVALUE_REF
+ && TYPE_CODE (TYPE_TARGET_TYPE (arg)) == TYPE_CODE_FUNC)
+ {
+ return (sum_ranks (rank_one_type (parm,
+ lookup_pointer_type (TYPE_TARGET_TYPE (arg)), NULL),
+ DIFFERENT_REFERENCE_TYPE_BADNESS));
+ }
+
+ /* If a conversion to one type of reference is an identity conversion, and a
+ conversion to the second type of reference is a non-identity conversion,
+ choose the first type. */
+
+ if (value != NULL && TYPE_IS_REFERENCE (parm) && TYPE_IS_REFERENCE (arg)
+ && TYPE_CODE (parm) != TYPE_CODE (arg))
+ {
+ return (sum_ranks (rank_one_type (TYPE_TARGET_TYPE (parm),
+ TYPE_TARGET_TYPE (arg), NULL), DIFFERENT_REFERENCE_TYPE_BADNESS));
+ }
+
+ /* An rvalue should be first tried to bind to an rvalue reference, and then to
+ an lvalue reference. */
+
+ if (value != NULL && TYPE_CODE (parm) == TYPE_CODE_REF
+ && VALUE_LVAL (value) == not_lval)
+ {
+ if (TYPE_IS_REFERENCE (arg))
+ arg = TYPE_TARGET_TYPE (arg);
+ return (sum_ranks (rank_one_type (TYPE_TARGET_TYPE (parm), arg, NULL),
+ LVALUE_REFERENCE_TO_RVALUE_BINDING_BADNESS));
+ }
+
/* See through references, since we can almost make non-references
references. */

--
2.1.0