mirror of
https://forge.sourceware.org/marek/gcc.git
synced 2026-02-22 12:00:11 -05:00
0120cd9382
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.
29 lines
595 B
C
29 lines
595 B
C
// PR c++/100209
|
|
// { dg-do compile { target c++14 } }
|
|
|
|
template<typename Derived>
|
|
struct __a_t
|
|
{
|
|
unsigned char A = 0;
|
|
constexpr Derived & SetA(const unsigned char & value) {
|
|
A = value;
|
|
return *static_cast<Derived *>(this);
|
|
}
|
|
};
|
|
|
|
template<typename Derived>
|
|
struct __b_t
|
|
{
|
|
unsigned char B = 0;
|
|
constexpr Derived & SetB(const unsigned char & value) {
|
|
B = value;
|
|
return *static_cast<Derived *>(this);
|
|
}
|
|
};
|
|
|
|
struct __ab_t : __a_t<__ab_t>, __b_t<__ab_t> { };
|
|
|
|
constexpr auto AB = __ab_t().SetA(100).SetB(10);
|
|
static_assert(AB.A == 100, "");
|
|
static_assert(AB.B == 10, "");
|