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What is hipCUB?

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What is hipCUB?#

hipCUB is a thin header-only wrapper library on top of rocPRIM or CUB. It enables developers to port project using CUB library to the HIP layer and to run them on AMD hardware. In the ROCm environment, hipCUB uses rocPRIM library as the backend, while on CUDA platforms it uses CUB.

Here are some key points to be noted:

  • When using hipCUB, include only <hipcub/hipcub.hpp> header.

  • When rocPRIM is used as backend, HIPCUB_ROCPRIM_API is defined.

  • When CUB is used as backend, HIPCUB_CUB_API is defined.

  • Backends are automatically selected based on the platform detected by HIP layer (__HIP_PLATFORM_AMD__, __HIP_PLATFORM_NVIDIA__).

rocPRIM backend#

hipCUB with the rocPRIM backend may not support all the CUB functions and features because of the differences between the ROCm (HIP) platform and the CUDA platform.

Unsupported features and differences:

  • Functions, classes, and macros that are not in the public API or undocumented are not supported.

  • Device-wide primitives can’t be called from kernels (dynamic parallelism is not supported in HIP on ROCm).

  • DeviceSpmv is not supported.

  • Fancy iterators: CacheModifiedInputIterator, CacheModifiedOutputIterator, and TexRefInputIterator are not supported.

  • Thread I/O:

    • CacheLoadModifier, CacheStoreModifier cache modifiers are not supported.

    • ThreadLoad, ThreadStore functions are not supported.

  • Storage management and debug functions:

    • Debug, PtxVersion, SmVersion functions and CubDebug, CubDebugExit, _CubLog macros are not supported.

  • Intrinsics:

    • ThreadExit, ThreadTrap are not supported.

    • Warp thread masks (when used) are 64-bit unsigned integers.

    • member_mask input argument is ignored in WARP_* functions.

    • Arguments first_lane, last_lane, and member_mask are ignored in Shuffle* functions.

  • Utilities:

    • SwizzleScanOp, ReduceBySegmentOp, ReduceByKeyOp, CastOp are not supported.

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