CCCL 2.x ‐ CCCL 3.0 migration guide

The CCCL team plans breaking changes carefully and only conducts them at major releases. The CCCL 2.8 release came with many deprecations to prepare for the breaking changes conducted in CCCL 3.0. This page summarizes the changes and helps migrating from CCCL 2.x to CCCL 3.0.

Removed macros

CUB_IS_INT128_ENABLED: No replacement
CUB_MAX(a, b): Use the cuda::std::max(a, b) function instead
CUB_MIN(a, b): Use the cuda::std::min(a, b) function instead
CUB_QUOTIENT_CEILING(a, b): Use cuda::ceil_div(a, b) instead
CUB_QUOTIENT_FLOOR(a, b): Use plain integer division a / b instead
CUB_ROUND_DOWN_NEAREST(a, b): Use cuda::round_down(a, b) instead
CUB_ROUND_UP_NEAREST(a, b): Use cuda::round_up(a, b) instead
CUB_RUNTIME_ENABLED: No replacement
CUB_USE_COOPERATIVE_GROUPS: No replacement
CUDA_CUB_RET_IF_FAIL: No replacement
[THRUST|CUB]_CLANG_VERSION: No replacement
[THRUST|CUB]_DEVICE_COMPILER*: No replacement
[THRUST|CUB]_GCC_VERSION: No replacement
[THRUST|CUB]_HOST_COMPILER*: No replacement
[THRUST|CUB]_INCLUDE_DEVICE_CODE: No replacement
[THRUST|CUB]_INCLUDE_HOST_CODE: No replacement
[THRUST|CUB]_IS_DEVICE_CODE: No replacement
[THRUST|CUB]_IS_HOST_CODE: No replacement
[THRUST|CUB]_MSVC_VERSION_FULL: No replacement
[THRUST|CUB]_MSVC_VERSION: No replacement
THRUST_CDP_DISPATCH: No replacement (Support for CUDA Dynamic Parallelism V1 (CDPv1) has been removed, see below)
THRUST_DECLTYPE_RETURNS_WITH_SFINAE_CONDITION: No replacement
THRUST_DECLTYPE_RETURNS: No replacement
THRUST_DEVICE_CODE: No replacement
THRUST_HOST_BACKEND: Use THRUST_HOST_SYSTEM instead
THRUST_INLINE_CONSTANT: Use inline constexpr instead
THRUST_INLINE_INTEGRAL_MEMBER_CONSTANT: Use static constexpr instead
THRUST_LEGACY_GCC: No replacement
THRUST_MODERN_GCC_REQUIRED_NO_ERROR: No replacement
THRUST_MODERN_GCC: No replacement
THRUST_MVCAP: No replacement
THRUST_NODISCARD: Use [[nodiscard]] instead
THRUST_RETOF1: No replacement
THRUST_RETOF2: No replacement
THRUST_RETOF: No replacement
THRUST_TUNING_ARCH: No direct replacement. Use compiler-specific __CUDA_ARCH__ (nvcc) or __NVCOMPILER_CUDA_ARCH__ (nvc++) instead

Removed functions and classes

_ReadWriteBarrier and __thrust_compiler_fence: Use cuda::atomic instead
cub::*Kernel: Any CUB kernel entrypoint is considered an implementation detail. No public exposure is provided.
cub::Agent*: CUB agents were considered implementation details and have all been moved to internal namespaces. No public exposure is provided.
cub::AliasTemporaries: No replacement
cub::ArrayWrapper: Use cuda::std::array instead
cub::BAR: No replacement
cub::BaseTraits::CATEGORY: Use the facilities from <cuda/std/type_traits> instead
cub::BaseTraits::NULL_TYPE: No replacement
cub::BaseTraits::PRIMITIVE: Use the facilities from <cuda/std/type_traits> instead
cub::BFI: Use cuda::bitfield_insert instead
cub::BinaryOpHasIdxParam::HAS_PARAM: Use cub::BinaryOpHasIdxParam::value instead
cub::ConstantInputIterator: Use thrust::constant_iterator instead
cub::CountingInputIterator: Use thrust::counting_iterator instead
cub::CTA_SYNC_AND: Use __syncthreads_and() instead
cub::CTA_SYNC_OR: Use __syncthreads_or() instead
cub::CTA_SYNC: Use __syncthreads() instead
cub::Device*Policy: Those policy hubs are considered implementation details. No public exposure is provided.
cub::DeviceSpmv: Use cuSPARSE instead
cub::Difference: Use cuda::std::minus instead
cub::DivideAndRoundUp: Use cuda::round_up instead
cub::Division: Use cuda::std::divides instead
cub::Equality: Use cuda::std::equal_to instead
cub::FFMA_RZ: No replacement
cub::FMUL_RZ: No replacement
cub::FpLimits<T>: Use cuda::std::numeric_limits<T> instead
cub::GridBarrier: Use the APIs from cooperative groups instead
cub::GridBarrierLifetime: Use the APIs from cooperative groups instead
cub::IADD3: No replacement
cub::Inequality: Use cuda::std::not_equal_to instead
cub::Int2Type: Use cuda::std::integral_constant instead
cub::IterateThreadLoad: No replacement
cub::IterateThreadStore: No replacement
cub::KernelConfig: No replacement
cub::LaneId(): Use cuda::ptx::get_sreg_laneid() instead
cub::LaneMaskGe(): Use cuda::ptx::get_sreg_lanemask_ge() instead
cub::LaneMaskGt(): Use cuda::ptx::get_sreg_lanemask_gt() instead
cub::LaneMaskLe(): Use cuda::ptx::get_sreg_lanemask_le() instead
cub::LaneMaskLt(): Use cuda::ptx::get_sreg_lanemask_lt() instead
cub::MakePolicyWrapper: No replacement
cub::Max: Use cuda::maximum instead
cub::max: Use cuda::std::max instead
cub::MemBoundScaling: No replacement
cub::Min: Use cuda::minimum instead
cub::min: Use cuda::std::min instead
cub::Mutex: Use std::mutex instead
cub::PolicyWrapper: No replacement
cub::PRMT: Use cuda::ptx::prmt() instead
cub::RegBoundScaling: No replacement
cub::SHFL_IDX_SYNC: Use __shfl_sync() instead
cub::SHL_ADD: No replacement
cub::SHR_ADD: No replacement
cub::Sum: Use cuda::std::plus instead
cub::Swap(a, b): Use cuda::std::swap(a, b) instead
cub::ThreadTrap(): Use cuda::std::terminate() instead
cub::TransformInputIterator: Use thrust::transform_iterator instead
cub::TripleChevronFactory: No replacement for now, we are working on a new kernel launch facility
cub::ValueCache: No replacement
cub::WARP_ALL: Use __all_sync() instead
cub::WARP_ANY: Use __any_sync() instead
cub::WARP_BALLOT: Use __ballot_sync() instead
cub::WARP_SYNC: Use __syncwarp() instead
cub::WarpId(): Use cuda::ptx::get_sreg_warpid() instead
thrust::*::[first_argument_type|second_argument_type|result_type]: The nested aliases have been removed for all function object types: thrust::[plus|minus|multiplies|divides|modulus|negate|square|equal_to|not_equal_to|greater|less|greater_equal|less_equal|logical_and|logical_or|logical_not|bit_and|bit_or|bit_xor|identity|maximum|minimum|project1st|project2nd]. No replacement.
thrust::[unary|binary]_function: No replacement. If you inherit from one of these types, just remove those base classes.
thrust::[unary|binary]_traits: No replacement.
thrust::async::*: No replacement for now. We are working on a C++26 senders implementation. For make a thrust algorithm skip syncing, use thrust::cuda::par_nosync as execution policy.
thrust::bidirectional_universal_iterator_tag: No replacement
thrust::conjunction_value<Ts...>: Use cuda::std::bool_constant<(Ts && ...)> instead
thrust::conjunction_value_v<Ts...>: Use a fold expression: Ts && ... instead
thrust::cuda_cub::core::*: Those are considered implementation details. No public exposure is provided.
thrust::cuda_cub::counting_iterator_t: Use thrust::counting_iterator instead
thrust::cuda_cub::identity: Use cuda::std::identity instead
thrust::cuda_cub::launcher::triple_chevron: No replacement for now, we are working on a new kernel launch facility
thrust::cuda_cub::terminate: Use cuda::std::terminate() instead
thrust::cuda_cub::transform_input_iterator_t: Use thrust::transform_iterator instead
thrust::cuda_cub::transform_pair_of_input_iterators_t: Use thrust::transform_iterator of a thrust::zip_iterator instead
thrust::disjunction_value<Ts...>: Use cuda::std::bool_constant<(Ts || ...)> instead
thrust::disjunction_value_v<Ts...>: Use a fold expression: Ts || ... instead
thrust::forward_universal_iterator_tag: No replacement
thrust::identity<T>: Use cuda::std::identity instead. If thrust::identity was used to perform a cast to T, please define your own function object.
thrust::input_universal_iterator_tag: No replacement
thrust::negation_value<T>: Use cuda::std::bool_constant<!T> instead
thrust::negation_value_v<T>: Use a plain negation !T
thrust::not[1|2]: Use cuda::std::not_fn instead
thrust::null_type: No replacement
thrust::numeric_limits<T>: Use cuda::std::numeric_limits<T> instead
thrust::optional<T>: Use cuda::std::optional<T> instead.
thrust::output_universal_iterator_tag: No replacement
thrust::random_access_universal_iterator_tag: No replacement
thrust::remove_cvref[_t]: Use cuda::std::remove_cvref[_t] instead
thrust::void_t: Use cuda::std::void_t instead

Deprecations with planned removal

CUB_LOG_SMEM_BANKS: No replacement
CUB_LOG_WARP_THREADS: No replacement
CUB_MAX_DEVICES: No replacement
CUB_PREFER_CONFLICT_OVER_PADDING: No replacement
CUB_PTX_LOG_SMEM_BANKS: No replacement
CUB_PTX_LOG_WARP_THREADS: No replacement
CUB_PTX_PREFER_CONFLICT_OVER_PADDING: No replacement
CUB_PTX_SMEM_BANKS: No replacement
CUB_PTX_SUBSCRIPTION_FACTOR: No replacement
CUB_PTX_WARP_THREADS: No replacement
CUB_SMEM_BANKS: No replacement
CUB_SUBSCRIPTION_FACTOR: No replacement
CUB_WARP_THREADS: No replacement
THRUST_FALSE: No replacement
THRUST_PREVENT_MACRO_SUBSTITUTION: No replacement
THRUST_STATIC_ASSERT(expr): Use static_assert(expr) instead
THRUST_TRUE: No replacement
THRUST_UNKNOWN: No replacement
THRUST_UNUSED_VAR: No replacement
cub::BFE: Use cuda::bitfield_extract instead
cub::MergePathSearch: No replacement
cub::Traits<T>::Max(): Use cuda::std::numeric_limits<T>::max() instead
cub::Traits<T>::Min(): Use cuda::std::numeric_limits<T>::min() instead
thrust::iterator_difference[_t]<T>: Use cuda::std::iterator_traits<T>::difference_type or cuda::std::iter_difference_t<T> instead
thrust::iterator_pointer[_t]<T>: Use cuda::std::iterator_traits<T>::pointer instead
thrust::iterator_reference[_t]<T>: Use cuda::std::iterator_traits<T>::reference or cuda::std::iter_reference_t<T> instead
thrust::iterator_traits<T>: Use cuda::std::iterator_traits<T> instead
thrust::iterator_value[_t]<T>: Use cuda::std::iterator_traits<T>::value_type or cuda::std::iter_value_t<T> instead

API breaks

cub::Block*: All trailing int LEGACY_PTX_ARCH template parameters have been removed
cub::CachingAllocator: The constructor taking a trailing bool debug parameter has been removed
cub::Device*: All overloads with a trailing bool debug_synchronous parameter have been removed
cub::Dispatch*: All Boolean template parameters have been replaced by enumerations to increase readability
cub::Dispatch*: All policy hub template parameters have been moved to the back of the template parameters list
cub::DispatchScan[ByKey]: The offset type must be an unsigned type of at least 4-byte size
cuda::ceil_div: Now returns the common type of its arguments
thrust::pair: Is now an alias to cuda::std::pair and no longer a distinct type
thrust::tabulate_output_iterator: The value_type has been fixed to be void
thrust::transform_iterator: Upon copying, will now always copy its contained function. If the contained function is neither copy constructible nor copy assignable, the iterator fails to compile when attempting to be copied.
thrust::tuple: Is now an alias to cuda::std::tuple and no longer a distinct type
thrust::universal_host_pinned_memory_resource: The alias has changed to a different memory resource, potentially changing pointer types derived from an allocator/container using this memory resource.
The following Thrust function object types have been made aliases to the equally-named types in cuda::std::: thrust::[plus|minus|multiplies|divides|modulus|negate|equal_to|not_equal_to|greater|less|greater_equal|less_equal|logical_and|logical_or|logical_not|bit_and|bit_or|bit_xor|identity|maximum|minimum]. No replacement.
CUB_DEFINE_DETECT_NESTED_TYPE: The generated detector trait no longer provides a ::VALUE member. Use ::value instead.

Iterator traits

cuda::std::iterator_traits will now correctly recognize user-provided specializations of std::iterator_traits. All of Thrust’s iterator traits have been redefined in terms of cuda::std::iterator_traits, and users should prefer to use iterator traits from libcu++. thrust::iterator_traits can no longer be specialized. Users should prefer to specialize cuda::std::iterator_traits instead of std::iterator_traits when necessary, to make their iterators work equally in device code.

CUB Traits

The functionality and internal use of cub::Traits has been minimized, because libcu++ provides better and standard alternatives. Only the use in CUB’s radix sort implementation for bit-twiddling remains. Floating-point limits should be obtained using cuda::std::numeric_limits<T> instead of cub::FpLimits<T>. Classification of types should be done with the facilities from <cuda/std/type_traits> and <cuda/type_traits>, notably with cuda::std::is_signed[_v], cuda::std::is_integral[_v], etc. There is an important difference for extended floating point types though: Since cuda::std::is_floating_point[_v] will only recognize C++ standard floating point types, cuda::is_floating_point[_v] must be used to correctly classify extended floating point types like __half or __nv_bfloat16. cub::BaseTraits and cub::Traits can no longer be specialized for custom types, and cub::FpLimits has been removed.

We acknowledge the need to provide user-defined floating point types though, e.g., registering a custom half type with CUB to be used in radix sort. Therefore, users can still specialize cub::NumericTraits for their custom floating point types, inheriting from cub::BaseTraits and providing the necessary information for the type. Additionally, the traits from libcu++ have to be specialized as well:

For example, a custom floating point type my_half could be registered with CUB and libcu++ like this:

template <>
inline constexpr bool ::cuda::is_floating_point_v<my_half> = true;

template <>
class ::cuda::std::numeric_limits<my_half> {
public:
  static constexpr bool is_specialized = true;
  static __host__ __device__ my_half max()    { return /* TODO */; }
  static __host__ __device__ my_half min()    { return /* TODO */; }
  static __host__ __device__ my_half lowest() { return /* TODO */; }
};

template <>
struct CUB_NS_QUALIFIER::NumericTraits<my_half> : BaseTraits<FLOATING_POINT, true, uint16_t, my_half> {};

Behavioral changes

cub::DeviceReduce::[Arg][Max|Min]: Will now use cuda::std::numeric_limits<T>::[max|min]() instead of cub::Traits to determine the initial value
cuda::std::mdspan: The implementation was entirely rewritten and you may experience subtle behavioral changes
thrust::transform_iterator: The logic to determine the reference type has been reworked, especially wrt. to functions that return references to their own arguments (e.g., thrust::identity).
thrust::transform_iterator::difference_type: The logic to select the difference type has been reworked. It’s now either int or ptrdiff.

ABI breaks

All of libcu++’s old ABI namespaces have been removed

Platform support

At least C++17 is required
At least clang 14 is required
At least GCC 7 is required
On Windows, at least Visual Studio 2019 is required (MSC_VER >= 1920)
Intel ICC (icpx) is no longer supported
At least CUDA Toolkit 12.0 is required
Support for CUDA Dynamic Parallelism V1 (CDPv1) has been removed
At least a GPU with compute capability 50 (Maxwell) is required