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Re: C++: taking address of const object with non-const operator&
On May 17, 2002, Jason Merrill <jason@redhat.com> wrote:
>>>>>> "Alexandre" == Alexandre Oliva <aoliva@redhat.com> writes:
>> Yet another error condition whose testcase I'm not allowed to
>> contribute :-(
> If you can't contribute the original testcase, then create a new
> one. Or if you're worried about contamination, ask someone else to.
This is exactly what I'm doing by posting the description. Sorry if
this was not clear.
> Here, I'll write you a new testcase for this bug:
Thanks. I've included it in the patch below.
> No, -fpermissive should not change behavior.
I see.
> Rather, we should always reject bad candidates for op&, op-> and
> op,.
I don't see the point of rejecting candidates for `op->'. It's not
like there would ever be a built-in operand that would match, so it
appears to me that the extension is safe in this case. Am I missing
anything, or is this patch ok to install? Tested on
athlon-pc-linux-gnu.
Index: gcc/cp/ChangeLog
from Alexandre Oliva <aoliva@redhat.com>
* call.c (any_strictly_viable): New.
(build_new_op): Use it for COMPOUND_EXPR and ADDR_EXPRs.
Index: gcc/cp/call.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cp/call.c,v
retrieving revision 1.318
diff -u -p -r1.318 call.c
--- gcc/cp/call.c 19 Apr 2002 06:22:13 -0000 1.318
+++ gcc/cp/call.c 19 May 2002 09:10:21 -0000
@@ -62,6 +62,7 @@ static void print_z_candidates PARAMS ((
static tree build_this PARAMS ((tree));
static struct z_candidate * splice_viable PARAMS ((struct z_candidate *));
static int any_viable PARAMS ((struct z_candidate *));
+static int any_strictly_viable PARAMS ((struct z_candidate *));
static struct z_candidate * add_template_candidate
PARAMS ((struct z_candidate *, tree, tree, tree, tree, tree, int,
unification_kind_t));
@@ -2319,6 +2320,16 @@ any_viable (cands)
return 0;
}
+static int
+any_strictly_viable (cands)
+ struct z_candidate *cands;
+{
+ for (; cands; cands = cands->next)
+ if (cands->viable == 1)
+ return 1;
+ return 0;
+}
+
static struct z_candidate *
splice_viable (cands)
struct z_candidate *cands;
@@ -3228,6 +3239,7 @@ build_new_op (code, flags, arg1, arg2, a
enum tree_code code2 = NOP_EXPR;
tree templates = NULL_TREE;
tree conv;
+ bool viable_candidates;
if (arg1 == error_mark_node
|| arg2 == error_mark_node
@@ -3392,7 +3404,25 @@ build_new_op (code, flags, arg1, arg2, a
(candidates, code, code2, fnname, args, flags);
}
- if (! any_viable (candidates))
+ switch (code)
+ {
+ case COMPOUND_EXPR:
+ case ADDR_EXPR:
+ /* For these, the built-in candidates set is empty
+ [over.match.oper]/3. We don't want non-strict matches
+ because exact matches are always possible with built-in
+ operators. The built-in candidate set for COMPONENT_REF
+ would be empty too, but since there are no such built-in
+ operators, we accept non-strict matches for them. */
+ viable_candidates = any_strictly_viable (candidates);
+ break;
+
+ default:
+ viable_candidates = any_viable (candidates);
+ break;
+ }
+
+ if (! viable_candidates)
{
switch (code)
{
Index: gcc/testsuite/ChangeLog
2002-05-19 Jason Merrill <jason2redhat.com>
* g++.dg/ext/oper1.C: New test.
from David Billinghurst <David.Billinghurst@riotinto.com>
Index: gcc/testsuite/g++.dg/ext/oper1.C
===================================================================
RCS file: gcc/testsuite/g++.dg/ext/oper1.C
diff -N gcc/testsuite/g++.dg/ext/oper1.C
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ gcc/testsuite/g++.dg/ext/oper1.C 19 May 2002 09:10:27 -0000
@@ -0,0 +1,19 @@
+// { dg-do run }
+
+// Copyright 2002 Free Software Foundation
+// Contributed by Jason Merrill <jason@redhat.com>
+
+// Make sure the GNU extension of accepting dropping cv-qualifiers for
+// the implicit this argument does not kick in when taking the address
+// of an object, since this extension would change the meaning of a
+// well-defined program.
+
+struct A {
+ A* operator&() { return 0; }
+};
+
+int main ()
+{
+ const A a = {};
+ return (&a == 0);
+}
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist Professional serial bug killer