Re: [C++ Patch] PR 58102 aka DR 1405
Hi,
On 09/02/2014 05:45 PM, Jason Merrill wrote:
On 09/02/2014 11:07 AM, Paolo Carlini wrote:
Anyway, what about the below? Certainly works for the tests which we
have got.
Hmm. This is definitely an improvement, as it allows a subset of
a non-volatile glvalue of literal type that refers to a non-volatile
object whose lifetime began within the evalution of e
But it doesn't cover all of that, and in any case we shouldn't need to
explicitly handle that just for types with mutable subobjects.
I think perhaps it would be better to remove that hunk as in your
initial patch and replace it with a check in constant_value_1 and an
explanation in non_const_var_error.
In practice, I'm encountering a rather serious problem with moving away
the check, I'm looking more into it, but maybe I can already explain it
to you...
The issue, AFAICS, boils down to the difference itself between
cxx_eval_outermost_constant_expr and cxx_eval_constant_expression:
changing constant_value_1 means that in principle all the calls of the
latter (for VAR_DECLs) are impacted. Thus, for example, for the call at
the beginning of cxx_eval_component_reference:
struct A
{
int i;
mutable int j;
};
constexpr A a = { 0, 1 };
constexpr int i = a.i;
how do we avoid emitting a wrong error for the a of a.i?
Paolo.
Re: [C++ Patch] PR 58102 aka DR 1405
On 09/03/2014 06:53 AM, Paolo Carlini wrote:
The issue, AFAICS, boils down to the difference itself between
cxx_eval_outermost_constant_expr and cxx_eval_constant_expression:
changing constant_value_1 means that in principle all the calls of the
latter (for VAR_DECLs) are impacted.
Oh, right.
Thus, for example, for the call at
the beginning of cxx_eval_component_reference:
struct A
{
int i;
mutable int j;
};
constexpr A a = { 0, 1 };
constexpr int i = a.i;
how do we avoid emitting a wrong error for the a of a.i?
Perhaps when we get the value of a we replace the mutable initializer
with a magic mutable value and then make sure what we return from
_outermost_ doesn't contain it?
Jason
Re: [C++ Patch] PR 58102 aka DR 1405
Hi,
On 09/02/2014 04:11 PM, Jason Merrill wrote:
On 09/01/2014 09:47 AM, Paolo Carlini wrote:
-constexpr A b = a;// { dg-error mutable }
+constexpr A b = a;
This is wrong; we still need to get an error here.
Hum, interesting. Neither current EDG nor current clang error out there.
Let's see if I can tease the case out...
Thanks,
Paolo.
Re: [C++ Patch] PR 58102 aka DR 1405
On 09/01/2014 09:47 AM, Paolo Carlini wrote:
-constexpr A b = a; // { dg-error mutable }
+constexpr A b = a;
This is wrong; we still need to get an error here.
Jason
Re: [C++ Patch] PR 58102 aka DR 1405
On 09/02/2014 10:17 AM, Paolo Carlini wrote:
Let's see if I can tease the case out...
I think you need to leave that hunk alone, and instead fix the new
testcase by treating = {} more like {}, just as we already don't require
a copy constructor call for copy-list-initialization.
Jason
Re: [C++ Patch] PR 58102 aka DR 1405
Hi,
On 09/02/2014 04:28 PM, Jason Merrill wrote:
On 09/02/2014 10:17 AM, Paolo Carlini wrote:
Let's see if I can tease the case out...
I think you need to leave that hunk alone, and instead fix the new
testcase by treating = {} more like {}, just as we already don't
require a copy constructor call for copy-list-initialization.
I see. Thanks a lot for the tip!
Paolo.
Re: [C++ Patch] PR 58102 aka DR 1405
Hi again,
On 09/02/2014 04:28 PM, Jason Merrill wrote:
On 09/02/2014 10:17 AM, Paolo Carlini wrote:
Let's see if I can tease the case out...
I think you need to leave that hunk alone, and instead fix the new
testcase by treating = {} more like {}, just as we already don't
require a copy constructor call for copy-list-initialization.
By the way, now I really understand the DR (the wording in the
resolution clarifies what we are *already* doing correctly!).
Anyway, what about the below? Certainly works for the tests which we
have got.
Thanks,
Paolo.
Index: cp/semantics.c
===
--- cp/semantics.c (revision 214808)
+++ cp/semantics.c (working copy)
@@ -9859,11 +9859,14 @@ cxx_eval_outermost_constant_expr (tree t, bool all
verify_constant (r, allow_non_constant, non_constant_p, overflow_p);
if (TREE_CODE (t) != CONSTRUCTOR
+ (TREE_CODE (t) != TARGET_EXPR
+ || TREE_CODE (TARGET_EXPR_INITIAL (t)) != AGGR_INIT_EXPR)
cp_has_mutable_p (TREE_TYPE (t)))
{
/* We allow a mutable type if the original expression was a
CONSTRUCTOR so that we can do aggregate initialization of
-constexpr variables. */
+constexpr variables. Likewise for TARGET_EXPRs with an
+AGGR_INIT_EXPR as TARGET_EXPR_INITIAL (c++/58102). */
if (!allow_non_constant)
error (%qT cannot be the type of a complete constant expression
because it has mutable sub-objects, TREE_TYPE (t));
Index: testsuite/g++.dg/cpp0x/constexpr-mutable2.C
===
--- testsuite/g++.dg/cpp0x/constexpr-mutable2.C (revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-mutable2.C (working copy)
@@ -0,0 +1,10 @@
+// DR 1405, PR c++/58102
+// { dg-do compile { target c++11 } }
+
+struct S {
+ mutable int n;
+ constexpr S() : n() {}
+};
+
+constexpr S s1 {};
+constexpr S s2 = {};
Re: [C++ Patch] PR 58102 aka DR 1405
On 09/02/2014 11:07 AM, Paolo Carlini wrote: Anyway, what about the below? Certainly works for the tests which we have got. Hmm. This is definitely an improvement, as it allows a subset of a non-volatile glvalue of literal type that refers to a non-volatile object whose lifetime began within the evalution of e But it doesn't cover all of that, and in any case we shouldn't need to explicitly handle that just for types with mutable subobjects. I think perhaps it would be better to remove that hunk as in your initial patch and replace it with a check in constant_value_1 and an explanation in non_const_var_error. Jason
[C++ Patch] PR 58102 aka DR 1405
Hi,
I think that in order to implement the resolution we simply have to
remove the check. Tested x86_64-linux.
Thanks,
Paolo.
//
/cp
2014-09-01 Paolo Carlini paolo.carl...@oracle.com
DR 1405
PR c++/58102
* semantics.c (cxx_eval_outermost_constant_expr): Do not check
for mutable sub-objects.
/testsuite
2014-09-01 Paolo Carlini paolo.carl...@oracle.com
DR 1405
PR c++/58102
* g++.dg/cpp0x/constexpr-mutable2.C: New.
* g++.dg/cpp0x/constexpr-mutable1.C: Adjust.
Index: cp/semantics.c
===
--- cp/semantics.c (revision 214779)
+++ cp/semantics.c (working copy)
@@ -9858,18 +9858,6 @@ cxx_eval_outermost_constant_expr (tree t, bool all
verify_constant (r, allow_non_constant, non_constant_p, overflow_p);
- if (TREE_CODE (t) != CONSTRUCTOR
- cp_has_mutable_p (TREE_TYPE (t)))
-{
- /* We allow a mutable type if the original expression was a
-CONSTRUCTOR so that we can do aggregate initialization of
-constexpr variables. */
- if (!allow_non_constant)
- error (%qT cannot be the type of a complete constant expression
- because it has mutable sub-objects, TREE_TYPE (t));
- non_constant_p = true;
-}
-
/* Technically we should check this for all subexpressions, but that
runs into problems with our internal representation of pointer
subtraction and the 5.19 rules are still in flux. */
Index: testsuite/g++.dg/cpp0x/constexpr-mutable1.C
===
--- testsuite/g++.dg/cpp0x/constexpr-mutable1.C (revision 214785)
+++ testsuite/g++.dg/cpp0x/constexpr-mutable1.C (working copy)
@@ -7,6 +7,6 @@ struct A
};
constexpr A a = { 0, 1 };
-constexpr A b = a; // { dg-error mutable }
+constexpr A b = a;
constexpr int i = a.i;
constexpr int j = a.j; // { dg-error mutable }
Index: testsuite/g++.dg/cpp0x/constexpr-mutable2.C
===
--- testsuite/g++.dg/cpp0x/constexpr-mutable2.C (revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-mutable2.C (working copy)
@@ -0,0 +1,10 @@
+// DR 1405, PR c++/58102
+// { dg-do compile { target c++11 } }
+
+struct S {
+ mutable int n;
+ constexpr S() : n() {}
+};
+
+constexpr S s1 {};
+constexpr S s2 = {};
