https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77598
Bug ID: 77598
Summary: consexpr compilation failure on reference type casting
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: bobk-off at yandex dot ru
Target Milestone: ---
Compiler fails on type casting of reference during constexpr processing. This
bug is actual for GCC-ARM 4.8.2+ compilers, and GCC-X86-64 5.3+ compilers
(tested on gcc.godbolt.org). clang of any version which supports C++14 compile
code below successfully.
Known walkaround: change type of dtarr variable to "DataTypeBasicX_t &"
#include <cstdint>
#include <array>
template<typename T>
struct DefaultInstanceOf { static constexpr T value = T(); };
template<typename T>
constexpr T DefaultInstanceOf<T>::value;
enum class BasicDataTypeId_t : uint16_t
{
None = 0,
INTEGER16 = 0x0003,
};
struct DataTypeX_t
{
private:
uint32_t mBitSize;
public:
constexpr uint32_t BitSize() const { return mBitSize; }
constexpr DataTypeX_t(const uint32_t & bitSize) : mBitSize(bitSize) {};
};
struct DataTypeBasicX_t : public DataTypeX_t
{
constexpr DataTypeBasicX_t() : DataTypeX_t(50) {};
};
struct DataTypeBasicArrayX_t : public DataTypeBasicX_t
{
};
struct BaseDataTypes
{
static constexpr const auto & ARRAY_OF_INT =
DefaultInstanceOf<DataTypeBasicArrayX_t>::value;
};
constexpr const DataTypeX_t & dtarr10 = BaseDataTypes::ARRAY_OF_INT;
constexpr const size_t bitsz10 = dtarr10.BitSize();
int main()
{
while (1);
}
Error message:
46 : in constexpr expansion of '(& dtarr10)->DataTypeX_t::BitSize()'
46 : error: accessing value of
'DefaultInstanceOf<DataTypeBasicArrayX_t>::value' through a 'const DataTypeX_t'
glvalue in a constant expression
constexpr const size_t bitsz10 = dtarr10.BitSize();
^
Compilation failed
Link to gcc.godbolt.org code: https://godbolt.org/g/lR0dE4
