https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109069
Bug ID: 109069
Summary: Vector truncation test program produces incorrect
result on big-endian powerpc64-linux-gnu with
-mcpu=power10 -O2
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: john_platts at hotmail dot com
Target Milestone: ---
The following C++ test program generates a test failure when compiled for
big-endian powerpc64-linux-gnu with GCC 12.2.1 with the -mcpu=power10 -O2
options:
#pragma push_macro("vector")
#pragma push_macro("pixel")
#pragma push_macro("bool")
#undef vector
#undef pixel
#undef bool
#include <altivec.h>
#pragma pop_macro("vector")
#pragma pop_macro("pixel")
#pragma pop_macro("bool")
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <iostream>
#include <string_view>
#include <type_traits>
template<size_t LaneSize>
struct AltivecTypes {
};
template<>
struct AltivecTypes<1> {
using UnsignedLaneT = unsigned char;
using SignedLaneT = signed char;
using UnsignedVectT = __vector unsigned char;
using SignedVectT = __vector signed char;
using BoolVectT = __vector __bool char;
};
template<>
struct AltivecTypes<2> {
using UnsignedLaneT = unsigned short;
using SignedLaneT = signed short;
using UnsignedVectT = __vector unsigned short;
using SignedVectT = __vector signed short;
using BoolVectT = __vector __bool short;
};
template<>
struct AltivecTypes<4> {
using UnsignedLaneT = unsigned int;
using SignedLaneT = signed int;
using FloatLaneT = float;
using UnsignedVectT = __vector unsigned int;
using SignedVectT = __vector signed int;
using BoolVectT = __vector __bool int;
using FloatVectT = __vector float;
};
template<>
struct AltivecTypes<8> {
using UnsignedLaneT = unsigned long long;
using SignedLaneT = signed long long;
using FloatLaneT = double;
using UnsignedVectT = __vector unsigned long long;
using SignedVectT = __vector signed long long;
using BoolVectT = __vector __bool long long;
using FloatVectT = __vector double;
};
template<class T, bool = std::is_signed_v<T>, bool = std::is_integral_v<T>,
bool = std::is_floating_point_v<T>, class = void>
struct MakeAltivecVectorType {
};
template<class T>
struct MakeAltivecVectorType<T, true, true, false,
std::void_t<typename AltivecTypes<sizeof(T)>::SignedVectT>> {
using type = typename AltivecTypes<sizeof(T)>::SignedVectT;
};
template<class T>
struct MakeAltivecVectorType<T, false, true, false,
std::void_t<typename AltivecTypes<sizeof(T)>::UnsignedVectT>> {
using type = typename AltivecTypes<sizeof(T)>::UnsignedVectT;
};
template<class T>
struct MakeAltivecVectorType<T, true, false, true,
std::void_t<typename AltivecTypes<sizeof(T)>::FloatVectT>> {
using type = typename AltivecTypes<sizeof(T)>::FloatVectT;
};
template<class T>
using AltivecVectorType = typename MakeAltivecVectorType<T>::type;
template<size_t N, class T, std::enable_if_t<(sizeof(T) * N <= 8)>* = nullptr>
AltivecVectorType<T> LoadVector(const T* __restrict__ src) {
using Bits = typename AltivecTypes<(sizeof(T) * N)>::UnsignedLaneT;
Bits bits;
__builtin_memcpy(&bits, src, sizeof(T) * N);
return reinterpret_cast<AltivecVectorType<T>>(vec_splats(bits));
}
template<size_t N, class T, std::enable_if_t<(sizeof(T) * N == 16)>* = nullptr>
AltivecVectorType<T> LoadVector(const T* __restrict__ src) {
using LaneT =
std::decay_t<decltype(std::declval<AltivecVectorType<T>>()[0])>;
typedef LaneT LoadRawT
__attribute__((__vector_size__(16), __aligned__(16), __may_alias__));
const LoadRawT* __restrict__ p = reinterpret_cast<const LoadRawT*>(src);
return reinterpret_cast<AltivecVectorType<T>>(*p);
}
template<size_t N, class T, std::enable_if_t<(sizeof(T) * N <= 8)>* = nullptr>
void StoreVector(T* __restrict__ dest, AltivecVectorType<T> vect) {
using Bits = typename AltivecTypes<(sizeof(T) * N)>::UnsignedLaneT;
typedef Bits BitsVectT __attribute__((__vector_size__(16)));
const Bits bits = reinterpret_cast<BitsVectT>(vect)[0];
__builtin_memcpy(dest, &bits, sizeof(T) * N);
}
template<size_t N, class T, std::enable_if_t<(sizeof(T) * N == 16)>* = nullptr>
void StoreVector(T* __restrict__ dest, AltivecVectorType<T> vect) {
using LaneT =
std::decay_t<decltype(std::declval<AltivecVectorType<T>>()[0])>;
typedef LaneT StoreRawT
__attribute__((__vector_size__(16), __aligned__(16), __may_alias__));
StoreRawT* __restrict__ p = reinterpret_cast<StoreRawT*>(dest);
*p = reinterpret_cast<StoreRawT>(vect);
}
template<size_t N, class FromV>
AltivecVectorType<uint8_t> AltivecTruncateToU8(FromV vect) {
static_assert(N >= 1, "N >= 1 must be true");
using FromLaneT = std::decay_t<decltype(std::declval<FromV>()[0])>;
constexpr size_t sizeOfFromLane = sizeof(FromLaneT);
static_assert(sizeOfFromLane >= 2, "sizeOfFromLane >= 2 must be true");
if constexpr(N == 1) {
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
return reinterpret_cast<__vector unsigned char>(vect);
#else
return reinterpret_cast<__vector unsigned char>(
vec_sld(vect, vect, sizeof(FromLaneT) - sizeof(unsigned char)));
#endif
} else {
if constexpr(sizeOfFromLane >= 4) {
return AltivecTruncateToU8<N>(vec_pack(vect, vect));
} else {
const __vector unsigned short u16Vect =
reinterpret_cast<__vector unsigned short>(vect);
return vec_pack(u16Vect, u16Vect);
}
}
}
static int TestsFailedCount = 0;
template<class T>
static constexpr decltype(auto) CharToNumber(T&& val) {
using DecayT = std::decay_t<T>;
if constexpr(std::is_same_v<DecayT, char>) {
if constexpr(std::is_signed_v<char>)
return static_cast<short>(val);
else
return static_cast<unsigned short>(val);
} else if constexpr(std::is_same_v<DecayT, signed char>) {
return static_cast<short>(val);
} else if constexpr(std::is_same_v<DecayT, unsigned char>) {
return static_cast<unsigned short>(val);
} else if constexpr(std::is_same_v<DecayT, char16_t>
#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
|| std::is_same_v<DecayT, char8_t>
#endif
) {
return static_cast<uint_least16_t>(val);
} else if constexpr(std::is_same_v<DecayT, char32_t>) {
return static_cast<uint_least32_t>(val);
} else if constexpr(std::is_same_v<DecayT, wchar_t>) {
if constexpr(std::is_signed_v<wchar_t>)
return static_cast<std::make_signed_t<wchar_t>>(val);
else
return static_cast<std::make_unsigned_t<wchar_t>>(val);
} else {
return static_cast<T&&>(val);
}
}
template<class T, size_t N>
inline void PrintValuesToCout(T (&vals)[N]) {
using namespace std::string_view_literals;
for(size_t i = 0; i < N; i++) {
if(i != 0)
std::cout << ", "sv;
std::cout << CharToNumber(vals[i]);
}
}
template<class FromLaneT, size_t N>
void DoTruncateToU8Test() {
using namespace std::string_view_literals;
{
constexpr uint32_t base = 0xFA578D00;
alignas(16) FromLaneT srcValues[N];
alignas(16) uint8_t expectedValues[N];
alignas(16) uint8_t actualValues[N];
for(size_t i = 0; i < N; i++) {
srcValues[i] =
static_cast<FromLaneT>(base + static_cast<FromLaneT>(i));
expectedValues[i] =
static_cast<uint8_t>(base + static_cast<uint8_t>(i));
}
auto srcVect =
LoadVector<N>(srcValues);
auto resultVect =
AltivecTruncateToU8<N>(srcVect);
StoreVector<N>(actualValues, resultVect);
for(size_t i = 0; i < N; i++) {
if(expectedValues[i] != actualValues[i]) {
std::cout << "Test failed for uint"sv <<
(sizeof(FromLaneT) << 3) <<
"_t lane type with "sv << N << " lanes\n"sv;
std::cout << "Expected values:\n "sv;
PrintValuesToCout(expectedValues);
std::cout << "\nActual values:\n "sv;
PrintValuesToCout(actualValues);
std::cout << '\n';
++TestsFailedCount;
break;
}
}
}
if constexpr(N >= 2) {
DoTruncateToU8Test<FromLaneT, N / 2>();
}
}
int main(int argc, char** argv) {
using namespace std::string_view_literals;
DoTruncateToU8Test<uint64_t, 2>();
DoTruncateToU8Test<uint32_t, 4>();
DoTruncateToU8Test<uint16_t, 8>();
const auto failCnt = TestsFailedCount;
std::cout << failCnt << " tests failed\n"sv;
return static_cast<int>(failCnt != 0);
}
Here is the expected output of the above program:
0 tests failed
Here is the output that is generated when the above program is compiled with
gcc 12.2.1 with the -mcpu=power10 -O2 options:
Test failed for uint32_t lane type with 1 lanes
Expected values:
0
Actual values:
250
Test failed for uint16_t lane type with 1 lanes
Expected values:
0
Actual values:
141
2 tests failed
The program above does generate the correct result when compiled with the
-mcpu=power9 -O2 options on the powerpc64-linux-gnu target.
The C++ test program above does generate the correct result if compiled with
clang 15 with the -mcpu=power10 -std=c++17 -O2 options.
