- [On HCC, can I link HIP code with host code compiled with another compiler such as gcc, icc, or clang ?](#on-hcc-can-i-link-hip-code-with-host-code-compiled-with-another-compiler-such-as-gcc-icc-or-clang-)
- CUPTI (not directly supported, [AMD GPUPerfAPI](http://developer.amd.com/tools-and-sdks/graphics-development/gpuperfapi/) can be used as an alternative in some cases)
- CUDA 6.0
- Managed memory (under development)
- CUDA 6.5
- __shfl instriniscs (supported)
- CUDA 7.0
- Per-thread-streams (under development)
- C++11 (HCC supports all of C++11, all of C++14 and some C++17 features)
HIP includes growing support for the 4 key math libraries using hcBlas, hcFft, hcrng and hcsparse.
These offer pointer-based memory interfaces (as opposed to opaque buffers) and can be easily interfaced with other HCC applications. Developers should use conditional compilation if portability to nvcc systems is desired - using calls to cu* routines on one path and hc* routines on the other.
Additionally, some of the cublas routines are automatically converted to hipblas equivalents by the hipify-clang tool. These APIs use cublas or hcblas depending on the platform, and replace the need
Both AMD and Nvidia support OpenCL 1.2 on their devices, so developers can write portable code.
HIP offers several benefits over OpenCL:
- Developers can code in C++ as well as mix host and device C++ code in their source files. HIP C++ code can use templates, lambdas, classes and so on.
- HIP uses the best available development tools on each platform: on Nvidia GPUs, HIP code compiles using NVCC and can employ the nSight profiler and debugger (unlike OpenCL on Nvidia GPUs).
- HIP provides pointers and host-side pointer arithmetic.
- HIP provides device-level control over memory allocation and placement.
HIP and CUDA provide similar math library calls as well. In summary, the HIP philosophy was to make the HIP language close enough to CUDA that the porting effort is relatively simple.
This reduces the potential for error, and also makes it easy to automate the translation. HIP's goal is to quickly get the ported program running on both platforms with little manual intervention,
so that the programmer can focus on performance optimizations.
There have been several tools that have attempted to convert CUDA into OpenCL, such as CU2CL. OpenCL is a C99-based kernel language (rather than C++) and also does not support single-source compilation.
- For AMD platforms, HIP runs on the same hardware that the HCC "hc" mode supports. See the ROCm documentation for the list of supported platforms.
- For Nvidia platforms, HIP requires Unified Memory and should run on any device supporting CUDA SDK 6.0 or newer. We have tested the Nvidia Titan and Tesla K40.
NVCC is Nvidia's compiler driver for compiling "CUDA C++" code into PTX or device code for Nvidia GPUs. It's a closed-source binary compiler that is provided by the CUDA SDK.
HCC is AMD's compiler driver which compiles "heterogeneous C++" code into HSAIL or GCN device code for AMD GPUs. It's an open-source compiler based on recent versions of CLANG/LLVM.
In addition, HIP defines portable mechanisms to query architectural features, and supports a larger 64-bit wavesize which expands the return type for cross-lane functions like ballot and shuffle from 32-bit ints to 64-bit ints.
Developers concerned about portability should of course run on both platforms, and should expect to tune for performance.
In some cases CUDA has a richer set of modes for some APIs, and some C++ capabilities such as virtual functions - see the HIP @API documentation for more details.
### Can I develop HIP code on an AMD HCC platform?
Yes. HIP's HCC path only exposes the APIs and functions that work on both NVCC and HCC back ends. "Extra" APIs, parameters and features that appear in HCC but not CUDA will typically cause compile- or run-time errors. Developers must use the HIP API for most accelerator code and bracket any HCC-specific code with preprocessor conditionals. Those concerned about portability should, of course, test their code on both platforms and should tune it for performance. Typically, HCC supports a more modern set of C++11/C++14/C++17 features, so HIP developers who want portability should be careful when using advanced C++ features on the hc path.
HIP is a source-portable language that can be compiled to run on either the HCC or NVCC platform. HIP tools don't create a "fat binary" that can run on either platform, however.
HIP is a portable C++ language that supports a strong subset of the CUDA run-time APIs and device-kernel language. It's designed to simplify CUDA conversion to portable C++. HIP provides a C-compatible run-time API, C-compatible kernel-launch mechanism, C++ kernel language and pointer-based memory management.
A C++ dialect, hc is supported by the AMD HCC compiler. It provides C++ run time, C++ kernel-launch APIs (parallel_for_each), C++ kernel language, and several memory-management options, including pointers, arrays and array_view (with implicit data synchronization). It's intended to be a leading indicator of the ISO C++ standard.
Yes. HIP/HCC generates the object code which conforms to the GCC ABI, and also links with libstdc++. This means you can compile host code with the compiler of your choice and link the generated object code
with GPU code compiled with HIP. Larger projects often contain a mixture of accelerator code (initially written in CUDA with nvcc) and host code (compiled with gcc, icc, or clang). These projects
can convert the accelerator code to HIP, compile that code with hipcc, and link with object code from their preferred compiler.
One symptom of this problem is the message "error: 'unknown error'(11) at square.hipref.cpp:56". This can occur if you have a CUDA installation on an AMD platform, and HIP incorrectly detects the platform as nvcc. HIP may be able to compile the application using the nvcc tool-chain, but will generate this error at runtime since the platform does not have a CUDA device. The fix is to set HIP_PLATFORM=hcc and rebuild.
If you see issues related to incorrect platform detection, please file an issue with the GitHub issue tracker so we can improve HIP's platform detection logic.
Yes. You can use HIP_PLATFORM to choose which path hipcc targets. This configuration can be useful when using HIP to develop an application which is portable to both AMD and NVIDIA.
Yes. Most HIP data structures (hipStream_t, hipEvent_t) are typedefs to CUDA equivalents and can be intermixed. Both CUDA and HIP use integer device ids.
One notable exception is that hipError_t is a new type, and cannot be used where a cudaError_t is expected. In these cases, refactor the code to remove the expectation. Alternatively, hip_runtime_api.h defines functions which convert between the error code spaces:
hipErrorToCudaError
hipCUDAErrorTohipError
hipCUResultTohipError
If platform portability is important, use #ifdef__HIP_PLATFORM_NVCC__ to guard the CUDA-specific code.
The code can include hc.hpp and use HC functions inside the kernel. A typical use-case is to use AMD-specific hardware features such as the permute, swizzle, or DPP operations.
