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* [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access
@ 2021-04-22 12:48 autumn.rain at mail dot ru
2021-04-22 13:14 ` [Bug c++/100209] " rguenth at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: autumn.rain at mail dot ru @ 2021-04-22 12:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Bug ID: 100209
Summary: multiple inheritance with crtp pattern fails on
sequentioal member access
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: autumn.rain at mail dot ru
Target Milestone: ---
If multiple inheritance is used with CRTP pattern in a constexpr context,
resulting class is failed to create.
When deriving AB from a single class (also with mani accessors) the constexpr
context is working well.
The error is reproduced on gcc since 6.1.x on any platform.
D:\>D:\0W\00Tools\2GCC_10.2_2020q4\bin\arm-none-eabi-g++ -Wall D:\Test.cpp
D:\Test.cpp:26:60: error: '*(const __ab_t*)(&(&
__ab_t().__ab_t::<anonymous>.__a
_t<__ab_t>::SetA(100))->__ab_t::<anonymous>.__b_t<__ab_t>::SetB(10))' is not a
c
onstant expression
26 | static constexpr const auto AB = __ab_t().SetA(100).SetB(10);
| ^
gcc version
10.2.1
template<typename TDERIVED>
struct __a_t
{
unsigned char A = 0;
constexpr TDERIVED & SetA(const unsigned char & value) { A = value;
return *static_cast<TDERIVED *>(this); }
constexpr __a_t() {}
};
template<typename TDERIVED>
struct __b_t
{
unsigned char B = 0;
constexpr TDERIVED & SetB(const unsigned char & value) { B = value;
return *static_cast<TDERIVED *>(this); }
constexpr __b_t() {}
};
class __ab_t: public __a_t<__ab_t>, public __b_t<__ab_t>
{
public:
constexpr __ab_t(){}
};
static constexpr const auto AB = __ab_t().SetA(100).SetB(10);
int A = 0;
int main()
{
A = AB.A;
}
How-To-Repeat:
Compile the attached code
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
@ 2021-04-22 13:14 ` rguenth at gcc dot gnu.org
2021-04-23 2:51 ` ppalka at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-04-22 13:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
clang accepts it
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
2021-04-22 13:14 ` [Bug c++/100209] " rguenth at gcc dot gnu.org
@ 2021-04-23 2:51 ` ppalka at gcc dot gnu.org
2021-04-23 4:28 ` ppalka at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-23 2:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
Last reconfirmed| |2021-04-23
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed. A bit more reduced:
struct A { int a = 0; };
template <class Derived>
struct B
{
int b = 0;
constexpr Derived f(int n) {
return *static_cast<Derived*>(this);
}
};
struct C : A, B<C> { };
constexpr C c = C().f(10);
100209.C:14:22: in ‘constexpr’ expansion of ‘C().C::<anonymous>.B<C>::f(10)’
100209.C:14:25: error: ‘*(const C*)((C*)(((B<C>*)this) + -4))’ is not a
constant expression
14 | constexpr C c = C().f(10);
| ^
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
2021-04-22 13:14 ` [Bug c++/100209] " rguenth at gcc dot gnu.org
2021-04-23 2:51 ` ppalka at gcc dot gnu.org
@ 2021-04-23 4:28 ` ppalka at gcc dot gnu.org
2021-04-23 4:29 ` ppalka at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-23 4:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
During cxx_eval_indirect_ref for
*(const struct C &) (const struct C *) (struct C *) ((struct B *) this + -4);
constant evaluation of the pointee yields
&D.2217.D.2106 + -4
where D.2217 is a temporary of type C and D.2106 is the FIELD_DECL for the base
B<C>. The problem seems to be that cxx_fold_indirect_ref doesn't know how to
fold this second expression to just
&D.2217
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
` (2 preceding siblings ...)
2021-04-23 4:28 ` ppalka at gcc dot gnu.org
@ 2021-04-23 4:29 ` ppalka at gcc dot gnu.org
2021-04-26 21:31 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-23 4:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
` (3 preceding siblings ...)
2021-04-23 4:29 ` ppalka at gcc dot gnu.org
@ 2021-04-26 21:31 ` cvs-commit at gcc dot gnu.org
2021-04-28 2:34 ` ppalka at gcc dot gnu.org
2021-11-06 23:40 ` ppalka at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-04-26 21:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:0120cd9382728fdc99d4cfdcb72cd0f55aca2ce3
commit r12-136-g0120cd9382728fdc99d4cfdcb72cd0f55aca2ce3
Author: Patrick Palka <ppalka@redhat.com>
Date: Mon Apr 26 17:30:39 2021 -0400
c++: constexpr pointer indirection with negative offset [PR100209]
During constexpr evaluation, a base-to-derived conversion may yield an
expression like (Derived*)(&D.2217.D.2106 p+ -4) where D.2217 is the
derived object and D.2106 is the base. But cxx_fold_indirect_ref
doesn't know how to resolve an INDIRECT_REF thereof to just D.2217,
because it doesn't handle POINTER_PLUS_EXPR of a COMPONENT_REF with
negative offset well: when the offset N is positive, it knows that
'&x p+ N' is equivalent to '&x.f p+ (N - bytepos(f))', but it doesn't
know about the reverse transformation, that '&x.f p+ N' is equivalent
to '&x p+ (N + bytepos(f))' when N is negative, which is important for
resolving such base-to-derived conversions and for accessing subobjects
backwards. This patch teaches cxx_fold_indirect_ref this reverse
transformation.
gcc/cp/ChangeLog:
PR c++/100209
* constexpr.c (cxx_fold_indirect_ref): Try to canonicalize the
object/offset pair for a POINTER_PLUS_EXPR of a COMPONENT_REF
with a negative offset into one whose offset is nonnegative
before calling cxx_fold_indirect_ref_1.
gcc/testsuite/ChangeLog:
PR c++/100209
* g++.dg/cpp1y/constexpr-base1.C: New test.
* g++.dg/cpp1y/constexpr-ptrsub1.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
` (4 preceding siblings ...)
2021-04-26 21:31 ` cvs-commit at gcc dot gnu.org
@ 2021-04-28 2:34 ` ppalka at gcc dot gnu.org
2021-11-06 23:40 ` ppalka at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-28 2:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
Target Milestone|--- |12.0
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12, thanks for the bug report.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
` (5 preceding siblings ...)
2021-04-28 2:34 ` ppalka at gcc dot gnu.org
@ 2021-11-06 23:40 ` ppalka at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-11-06 23:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |steven.vanderschoot@nextlev
| |el-electronics.com
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 97752 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 8+ messages in thread
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2021-04-22 12:48 [Bug c++/100209] New: multiple inheritance with crtp pattern fails on sequentioal member access autumn.rain at mail dot ru
2021-04-22 13:14 ` [Bug c++/100209] " rguenth at gcc dot gnu.org
2021-04-23 2:51 ` ppalka at gcc dot gnu.org
2021-04-23 4:28 ` ppalka at gcc dot gnu.org
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