[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 Patrick Palka changed: What|Removed |Added CC||steven.vanderschoot@nextlev ||el-electronics.com --- Comment #6 from Patrick Palka --- *** Bug 97752 has been marked as a duplicate of this bug. ***
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 Patrick Palka changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED Target Milestone|--- |12.0 --- Comment #5 from Patrick Palka --- Fixed for GCC 12, thanks for the bug report.
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 --- Comment #4 from CVS Commits --- The master branch has been updated by Patrick Palka : https://gcc.gnu.org/g:0120cd9382728fdc99d4cfdcb72cd0f55aca2ce3 commit r12-136-g0120cd9382728fdc99d4cfdcb72cd0f55aca2ce3 Author: Patrick Palka 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*)( 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 ' p+ N' is equivalent to ' p+ (N - bytepos(f))', but it doesn't know about the reverse transformation, that ' p+ N' is equivalent to ' 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.
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 Patrick Palka changed: What|Removed |Added Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org Status|NEW |ASSIGNED
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 --- Comment #3 from Patrick Palka --- During cxx_eval_indirect_ref for *(const struct C &) (const struct C *) (struct C *) ((struct B *) this + -4); constant evaluation of the pointee yields + -4 where D.2217 is a temporary of type C and D.2106 is the FIELD_DECL for the base B. The problem seems to be that cxx_fold_indirect_ref doesn't know how to fold this second expression to just
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209
Patrick Palka 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 ---
Confirmed. A bit more reduced:
struct A { int a = 0; };
template
struct B
{
int b = 0;
constexpr Derived f(int n) {
return *static_cast(this);
}
};
struct C : A, B { };
constexpr C c = C().f(10);
100209.C:14:22: in ‘constexpr’ expansion of ‘C().C::.B::f(10)’
100209.C:14:25: error: ‘*(const C*)((C*)(((B*)this) + -4))’ is not a
constant expression
14 | constexpr C c = C().f(10);
| ^
[Bug c++/100209] multiple inheritance with crtp pattern fails on sequentioal member access
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100209 Richard Biener changed: What|Removed |Added Keywords||rejects-valid --- Comment #1 from Richard Biener --- clang accepts it
