[review] gdb: rank an lvalue argument incompatible for an rvalue parameter
Commit Message
Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/752
......................................................................
gdb: rank an lvalue argument incompatible for an rvalue parameter
Passing an lvalue argument to a function that takes an rvalue parameter
is not allowed per C++ rules. Consider this function:
int g (int &&x) { return x; }
Calling g as in
int i = 5;
int j = g (i);
is illegal. For instance, GCC 9.2.1 yields
~~~
test.cpp: In function ‘int main()’:
test.cpp:6:14: error: cannot bind rvalue reference of type ‘int&&’ to
lvalue of type ‘int’
6 | int j = g (i);
| ^
~~~
GDB currently allows this function call:
~~~
(gdb) print g(i)
$1 = 5
~~~
Fix this by ranking an lvalue argument incompatible with an rvalue
parameter. The behavior after this patch is:
~~~
(gdb) print g(i)
Cannot resolve function g to any overloaded instance
~~~
Tested with GCC 9.2.1.
gdb/ChangeLog:
2019-12-09 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdbtypes.c (rank_one_type): Return INCOMPATIBLE_TYPE_BADNESS
when ranking an lvalue argument for an rvalue parameter.
gdb/testsuite/ChangeLog:
2019-12-09 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdb.cp/rvalue-ref-overload.cc (g): New function that takes
an rvalue parameter.
* gdb.cp/rvalue-ref-overload.exp: Test calling it with an lvalue
parameter.
Change-Id: I4a6dfc7dac63efa1e3b9f8f391e4b736fbdccdc1
---
M gdb/gdbtypes.c
M gdb/testsuite/gdb.cp/rvalue-ref-overload.cc
M gdb/testsuite/gdb.cp/rvalue-ref-overload.exp
3 files changed, 18 insertions(+), 5 deletions(-)
Comments
Simon Marchi has posted comments on this change.
Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/752
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Patch Set 1: Code-Review+2
LGTM, thanks for the nice commit message and the test!
@@ -4303,12 +4303,9 @@
}
else
{
- /* Lvalues should prefer lvalue overloads. */
+ /* It's illegal to pass an lvalue as an rvalue. */
if (TYPE_CODE (parm) == TYPE_CODE_RVALUE_REF)
- {
- rank.subrank = REFERENCE_CONVERSION_RVALUE;
- return sum_ranks (rank, REFERENCE_CONVERSION_BADNESS);
- }
+ return INCOMPATIBLE_TYPE_BADNESS;
}
}
@@ -62,6 +62,12 @@
return 3;
}
+static int
+g (int &&x)
+{
+ return x;
+}
+
int
main ()
{
@@ -78,6 +84,12 @@
int test_const // = 3
= foo_rr_instance1.overloadConst (arg);
+ /* The statement below is illegal: cannot bind rvalue reference of
+ type 'int&&' to lvalue of type 'int'.
+
+ result = g (i); */
+ result = g (5); // this is OK
+
marker1 (); // marker1-returns-here
return result;
}
@@ -66,3 +66,7 @@
setup_kfail "c++/15372" "*-*-*"
gdb_test "print f (3)" "3" "rvalue reference overload"
+
+gdb_test "print g (i)" \
+ "Cannot resolve function g to any overloaded instance" \
+ "passing lvalue arg to rvalue parameter"