[pushed] gdb: fix overload resolution for see-through references
Commit Message
Sourceware to Gerrit sync has submitted this change.
Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/617
......................................................................
gdb: fix overload resolution for see-through references
The overload resolution mechanism assigns badness values to the
necessary conversions to be made on types to pick a champion. A
badness value consists of a "rank" that scores the conversion and a
"subrank" to differentiate conversions of the same kind.
An auxiliary function, 'sum_ranks', is used for adding two badness
values. In all of its uses, except two, 'sum_ranks' is used for
populating the subrank of a badness value. The two exceptions are in
'rank_one_type':
~~~
/* See through references, since we can almost make non-references
references. */
if (TYPE_IS_REFERENCE (arg))
return (sum_ranks (rank_one_type (parm, TYPE_TARGET_TYPE (arg), NULL),
REFERENCE_CONVERSION_BADNESS));
if (TYPE_IS_REFERENCE (parm))
return (sum_ranks (rank_one_type (TYPE_TARGET_TYPE (parm), arg, NULL),
REFERENCE_CONVERSION_BADNESS));
~~~
Here, the result of a recursive call is combined with
REFERENCE_CONVERSION_BADNESS. This leads to the problem of
over-punishment by combining two ranks. Consider this:
void an_overloaded_function (const foo &);
void an_overloaded_function (const foo &&);
...
foo arg;
an_overloaded_function(arg);
When ranking 'an_overloaded_function (const foo &)', the badness
values REFERENCE_CONVERSION_BADNESS and CV_CONVERSION_BADNESS are
combined, whereas 'rank_one_type' assigns only the
REFERENCE_CONVERSION_BADNESS value to 'an_overloaded_function (const
foo &&)' (there is a different execution flow for that). This yields
in GDB picking the latter function as the overload champion instead of
the former.
In fact, the 'rank_one_type' function should have given
'an_overloaded_function (const foo &)' the CV_CONVERSION_BADNESS
value, with the see-through referencing increasing the subrank a
little bit. This can be achieved by introducing a new badness value,
REFERENCE_SEE_THROUGH_BADNESS, which bumps up the subrank only, and
using it in the two "exceptional" cases of 'sum_ranks'.
gdb/ChangeLog:
2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdbtypes.h: Define the REFERENCE_SEE_THROUGH_BADNESS value.
* gdbtypes.c (rank_one_type): Use REFERENCE_SEE_THROUGH_BADNESS
for ranking see-through reference cases.
gdb/testsuite/ChangeLog:
2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdb.cp/rvalue-ref-overload.cc: Add a case that involves both
CV and reference conversion for overload resolution.
* gdb.cp/rvalue-ref-overload.exp: Test it.
Change-Id: I39ae6505ab85ad0bd21915368c82540ceeb3aae9
---
M gdb/ChangeLog
M gdb/gdbtypes.c
M gdb/gdbtypes.h
M gdb/testsuite/ChangeLog
M gdb/testsuite/gdb.cp/rvalue-ref-overload.cc
M gdb/testsuite/gdb.cp/rvalue-ref-overload.exp
6 files changed, 29 insertions(+), 2 deletions(-)
@@ -1,3 +1,9 @@
+2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
+
+ * gdbtypes.h: Define the REFERENCE_SEE_THROUGH_BADNESS value.
+ * gdbtypes.c (rank_one_type): Use REFERENCE_SEE_THROUGH_BADNESS
+ for ranking see-through reference cases.
+
2019-12-06 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* stack.c (faas_command): Check a command is provided.
* thread.c (taas_command, tfaas_command): Likewise.
@@ -60,6 +60,7 @@
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 REFERENCE_SEE_THROUGH_BADNESS = {0,1};
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};
@@ -4338,10 +4339,10 @@
if (TYPE_IS_REFERENCE (arg))
return (sum_ranks (rank_one_type (parm, TYPE_TARGET_TYPE (arg), NULL),
- REFERENCE_CONVERSION_BADNESS));
+ REFERENCE_SEE_THROUGH_BADNESS));
if (TYPE_IS_REFERENCE (parm))
return (sum_ranks (rank_one_type (TYPE_TARGET_TYPE (parm), arg, NULL),
- REFERENCE_CONVERSION_BADNESS));
+ REFERENCE_SEE_THROUGH_BADNESS));
if (overload_debug)
/* Debugging only. */
fprintf_filtered (gdb_stderr,
@@ -2105,6 +2105,7 @@
/* * Badness of converting from non-reference to reference. Subrank
is the type of reference conversion being done. */
extern const struct rank REFERENCE_CONVERSION_BADNESS;
+extern const struct rank REFERENCE_SEE_THROUGH_BADNESS;
/* * Conversion to rvalue reference. */
#define REFERENCE_CONVERSION_RVALUE 1
/* * Conversion to const lvalue reference. */
@@ -1,3 +1,9 @@
+2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
+
+ * gdb.cp/rvalue-ref-overload.cc: Add a case that involves both
+ CV and reference conversion for overload resolution.
+ * gdb.cp/rvalue-ref-overload.exp: Test it.
+
2019-12-06 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* gdb.threads/pthreads.exp: Test taas and tfaas without command.
@@ -35,6 +35,8 @@
int overload1arg (foo_lval_ref);
int overload1arg (foo_rval_ref);
+ int overloadConst (const foo &);
+ int overloadConst (const foo &&);
};
void
@@ -71,6 +73,11 @@
// result = 1 + 2 + 3 + 3 = 9
int result = f (i) + f (ci) + f (0) + f (std::move (i));
+ /* Overload resolution below requires both a CV-conversion
+ and reference conversion. */
+ int test_const // = 3
+ = foo_rr_instance1.overloadConst (arg);
+
marker1 (); // marker1-returns-here
return result;
}
@@ -84,3 +91,5 @@
int foo::overload1arg (foo_lval_ref arg) { return 1; }
int foo::overload1arg (foo_rval_ref arg) { return 2; }
+int foo::overloadConst (const foo &arg) { return 3; }
+int foo::overloadConst (const foo &&arg) { return 4; }
@@ -49,6 +49,8 @@
{ method public "~foo();" }
{ method public "int overload1arg(foo_lval_ref);" }
{ method public "int overload1arg(foo_rval_ref);" }
+ { method public "int overloadConst(const foo &);" }
+ { method public "int overloadConst(const foo &&);" }
}
gdb_test "print foo_rr_instance1.overload1arg(arg)" \
@@ -59,6 +61,8 @@
"\\$\[0-9\]+ = 2" \
"print call overloaded func foo && arg"
+gdb_test "print foo_rr_instance1.overloadConst(arg)" "3"
+
# Test lvalue vs rvalue function overloads
gdb_test "print f (i)" "= 1" "lvalue reference overload"