Programming for HIP runtime compiler (RTC)

Programming for HIP runtime compiler (RTC)#

HIP supports the kernels compilation at runtime with the hiprtc* APIs. Kernels can be stored as a text string and can be passed to HIPRTC APIs alongside options to guide the compilation.

Note

  • This library can be used for compilation on systems without AMD GPU drivers installed (offline compilation). However, running the compiled code still requires both the HIP runtime library and GPU drivers on the target system.

  • This library depends on Code Object Manager (comgr). You can try to statically link comgr into HIPRTC to avoid ambiguity.

  • Developers can bundle this library with their application.

Compilation APIs#

To use HIPRTC functionality the header needs to be included:

#include <hip/hiprtc.h>

Kernels can be stored in a string:

static constexpr auto kernel_source {
R"(
    extern "C"
    __global__ void vector_add(float* output, float* input1, float* input2, size_t size) {
      int i = threadIdx.x;
      if (i < size) {
        output[i] = input1[i] + input2[i];
      }
    }
)"};

To compile this kernel, it needs to be associated with hiprtcProgram type, which is done by declaring hiprtcProgram prog; and associating the string of kernel with this program:

hiprtcCreateProgram(&prog,                 // HIPRTC program handle
                    kernel_source,         // HIP kernel source string
                    "vector_add.cpp",      // Name of the HIP program, can be null or an empty string
                    0,                     // Number of headers
                    NULL,                  // Header sources
                    NULL);                 // Name of header files

hiprtcCreateProgram() API also allows you to add headers which can be included in your RTC program. For online compilation, the compiler pre-defines HIP device API functions, HIP specific types and macros for device compilation, but doesn’t include standard C/C++ headers by default. Users can only include header files provided to hiprtcCreateProgram().

After associating the kernel string with hiprtcProgram, you can now compile this program using:

hiprtcCompileProgram(prog,     // hiprtcProgram
                    0,         // Number of options
                    options);  // Clang Options [Supported Clang Options](clang_options.md)

hiprtcCompileProgram() returns a status value which can be converted to string via hiprtcGetErrorString(). If compilation is successful, hiprtcCompileProgram() will return HIPRTC_SUCCESS.

if the compilation fails or produces warnings, you can look up the logs via:

size_t logSize;
hiprtcGetProgramLogSize(prog, &logSize);

if (logSize) {
  string log(logSize, '\0');
  hiprtcGetProgramLog(prog, &log[0]);
  // Corrective action with logs
}

If the compilation is successful, you can load the compiled binary in a local variable.

size_t codeSize;
hiprtcGetCodeSize(prog, &codeSize);

vector<char> kernel_binary(codeSize);
hiprtcGetCode(prog, kernel_binary.data());

After loading the binary, hiprtcProgram can be destroyed. hiprtcDestroyProgram(&prog);

The binary present in kernel_binary can now be loaded via hipModuleLoadData() API.

hipModule_t module;
hipFunction_t kernel;

hipModuleLoadData(&module, kernel_binary.data());
hipModuleGetFunction(&kernel, module, "vector_add");

And now this kernel can be launched via hipModule APIs.

The full example is below:

#include <hip/hip_runtime.h>
#include <hip/hiprtc.h>

#include <iostream>
#include <string>
#include <vector>

#define CHECK_RET_CODE(call, ret_code)                                                             \
  {                                                                                                \
    if ((call) != ret_code) {                                                                      \
      std::cout << "Failed in call: " << #call << std::endl;                                       \
      std::abort();                                                                                \
    }                                                                                              \
  }
#define HIP_CHECK(call) CHECK_RET_CODE(call, hipSuccess)
#define HIPRTC_CHECK(call) CHECK_RET_CODE(call, HIPRTC_SUCCESS)

// source code for hiprtc
static constexpr auto kernel_source{
    R"(
    extern "C"
    __global__ void vector_add(float* output, float* input1, float* input2, size_t size) {
      int i = threadIdx.x;
      if (i < size) {
        output[i] = input1[i] + input2[i];
      }
    }
)"};

int main() {
  hiprtcProgram prog;
  auto rtc_ret_code = hiprtcCreateProgram(&prog,            // HIPRTC program handle
                                          kernel_source,    // kernel source string
                                          "vector_add.cpp", // Name of the file
                                          0,                // Number of headers
                                          NULL,             // Header sources
                                          NULL);            // Name of header file

  if (rtc_ret_code != HIPRTC_SUCCESS) {
    std::cout << "Failed to create program" << std::endl;
    std::abort();
  }

  hipDeviceProp_t props;
  int device = 0;
  HIP_CHECK(hipGetDeviceProperties(&props, device));
  std::string sarg = std::string("--gpu-architecture=") +
      props.gcnArchName;  // device for which binary is to be generated

  const char* options[] = {sarg.c_str()};

  rtc_ret_code = hiprtcCompileProgram(prog,      // hiprtcProgram
                                      0,         // Number of options
                                      options);  // Clang Options
  if (rtc_ret_code != HIPRTC_SUCCESS) {
    std::cout << "Failed to create program" << std::endl;
    std::abort();
  }

  size_t logSize;
  HIPRTC_CHECK(hiprtcGetProgramLogSize(prog, &logSize));

  if (logSize) {
    std::string log(logSize, '\0');
    HIPRTC_CHECK(hiprtcGetProgramLog(prog, &log[0]));
    std::cout << "Compilation failed or produced warnings: " << log << std::endl;
    std::abort();
  }

  size_t codeSize;
  HIPRTC_CHECK(hiprtcGetCodeSize(prog, &codeSize));

  std::vector<char> kernel_binary(codeSize);
  HIPRTC_CHECK(hiprtcGetCode(prog, kernel_binary.data()));

  HIPRTC_CHECK(hiprtcDestroyProgram(&prog));

  hipModule_t module;
  hipFunction_t kernel;

  HIP_CHECK(hipModuleLoadData(&module, kernel_binary.data()));
  HIP_CHECK(hipModuleGetFunction(&kernel, module, "vector_add"));

  constexpr size_t ele_size = 256;  // total number of items to add
  std::vector<float> hinput, output;
  hinput.reserve(ele_size);
  output.reserve(ele_size);
  for (size_t i = 0; i < ele_size; i++) {
    hinput.push_back(static_cast<float>(i + 1));
    output.push_back(0.0f);
  }

  float *dinput1, *dinput2, *doutput;
  HIP_CHECK(hipMalloc(&dinput1, sizeof(float) * ele_size));
  HIP_CHECK(hipMalloc(&dinput2, sizeof(float) * ele_size));
  HIP_CHECK(hipMalloc(&doutput, sizeof(float) * ele_size));

  HIP_CHECK(hipMemcpy(dinput1, hinput.data(), sizeof(float) * ele_size, hipMemcpyHostToDevice));
  HIP_CHECK(hipMemcpy(dinput2, hinput.data(), sizeof(float) * ele_size, hipMemcpyHostToDevice));

  struct {
    float* output;
    float* input1;
    float* input2;
    size_t size;
  } args{doutput, dinput1, dinput2, ele_size};

  auto size = sizeof(args);
  void* config[] = {HIP_LAUNCH_PARAM_BUFFER_POINTER, &args, HIP_LAUNCH_PARAM_BUFFER_SIZE, &size,
                    HIP_LAUNCH_PARAM_END};

  HIP_CHECK(hipModuleLaunchKernel(kernel, 1, 1, 1, ele_size, 1, 1, 0, nullptr, nullptr, config));

  HIP_CHECK(hipMemcpy(output.data(), doutput, sizeof(float) * ele_size, hipMemcpyDeviceToHost));

  for (size_t i = 0; i < ele_size; i++) {
    if ((hinput[i] + hinput[i]) != output[i]) {
      std::cout << "Failed in validation: " << (hinput[i] + hinput[i]) << " - " << output[i]
                << std::endl;
      std::abort();
    }
  }
  std::cout << "Passed" << std::endl;

  HIP_CHECK(hipFree(dinput1));
  HIP_CHECK(hipFree(dinput2));
  HIP_CHECK(hipFree(doutput));
}

Kernel Compilation Cache#

HIPRTC incorporates a cache to avoid recompiling kernels between program executions. The contents of the cache include the kernel source code (including the contents of any #include headers), the compilation flags, and the compiler version. After a ROCm version update, the kernels are progressively recompiled, and the new results are cached. When the cache is disabled, each kernel is recompiled every time it is requested.

Use the following environment variables to manage the cache status as enabled or disabled, the location for storing the cache contents, and the cache eviction policy:

  • AMD_COMGR_CACHE By default this variable has a value of 0 and the compilation cache feature is disabled. To enable the feature set the environment variable to a value of 1 (or any value other than 0).

  • AMD_COMGR_CACHE_DIR: By default the value of this environment variable is defined as $XDG_CACHE_HOME/comgr_cache, which defaults to $USER/.cache/comgr_cache on Linux, and %LOCALAPPDATA%\cache\comgr_cache on Windows. You can specify a different directory for the environment variable to change the path for cache storage. If the runtime fails to access the specified cache directory, or the environment variable is set to an empty string (“”), the cache is disabled.

  • AMD_COMGR_CACHE_POLICY: If assigned a value, the string is interpreted and applied to the cache pruning policy. The string format is consistent with Clang’s ThinLTO cache pruning policy. The default policy is defined as: prune_interval=1h:prune_expiration=0h:cache_size=75%:cache_size_bytes=30g:cache_size_files=0. If the runtime fails to parse the defined string, or the environment variable is set to an empty string (“”), the cache is disabled.

Note

This cache is also shared with the OpenCL runtime shipped with ROCm.

HIPRTC specific options#

HIPRTC provides a few HIPRTC specific flags:

  • --gpu-architecture : This flag can guide the code object generation for a specific GPU architecture. Example: --gpu-architecture=gfx906:sramecc+:xnack-, its equivalent to --offload-arch.

    • This option is compulsory if compilation is done on a system without AMD GPUs supported by HIP runtime.

    • Otherwise, HIPRTC will load the hip runtime and gather the current device and its architecture info and use it as option.

  • -fgpu-rdc : This flag when provided during the hiprtcCreateProgram() generates the bitcode (HIPRTC doesn’t convert this bitcode into ISA and binary). This bitcode can later be fetched using hiprtcGetBitcode() and hiprtcGetBitcodeSize() APIs.

Bitcode#

In the usual scenario, the kernel associated with hiprtcProgram is compiled into the binary which can be loaded and run. However, if -fgpu-rdc option is provided in the compile options, HIPRTC calls comgr and generates only the LLVM bitcode. It doesn’t convert this bitcode to ISA and generate the final binary.

std::string sarg = std::string("-fgpu-rdc");
const char* options[] = {
    sarg.c_str() };
hiprtcCompileProgram(prog, // hiprtcProgram
                     1,    // Number of options
                     options);

If the compilation is successful, one can load the bitcode in a local variable using the bitcode APIs provided by HIPRTC.

size_t bitCodeSize;
hiprtcGetBitcodeSize(prog, &bitCodeSize);

vector<char> kernel_bitcode(bitCodeSize);
hiprtcGetBitcode(prog, kernel_bitcode.data());

CU Mode vs WGP mode#

AMD GPUs consist of an array of workgroup processors, each built with 2 compute units (CUs) capable of executing SIMD32. All the CUs inside a workgroup processor use local data share (LDS).

gfx10+ support execution of wavefront in CU mode and work-group processor mode (WGP). Please refer to section 2.3 of RDNA3 ISA reference.

gfx9 and below only supports CU mode.

In WGP mode, 4 warps of a block can simultaneously be executed on the workgroup processor, where as in CU mode only 2 warps of a block can simultaneously execute on a CU. In theory, WGP mode might help with occupancy and increase the performance of certain HIP programs (if not bound to inter warp communication), but might incur performance penalty on other HIP programs which rely on atomics and inter warp communication. This also has effect of how the LDS is split between warps, please refer to RDNA3 ISA reference for more information.

Note

HIPRTC assumes WGP mode by default for gfx10+. This can be overridden by passing -mcumode to HIPRTC compile options in hiprtcCompileProgram().

Linker APIs#

The bitcode generated using the HIPRTC Bitcode APIs can be loaded using hipModule APIs and also can be linked with other generated bitcodes with appropriate linker flags using the HIPRTC linker APIs. This also provides more flexibility and optimizations to the applications who want to generate the binary dynamically according to their needs. The input bitcodes can be generated only for a specific architecture or it can be a bundled bitcode which is generated for multiple architectures.

Example#

Firstly, HIPRTC link instance or a pending linker invocation must be created using hiprtcLinkCreate(), with the appropriate linker options provided.

hiprtcLinkCreate( num_options,           // number of options
                  options,               // Array of options
                  option_vals,           // Array of option values cast to void*
                  &rtc_link_state );     // HIPRTC link state created upon success

Following which, the bitcode data can be added to this link instance via hiprtcLinkAddData() (if the data is present as a string) or hiprtcLinkAddFile() (if the data is present as a file) with the appropriate input type according to the data or the bitcode used.

hiprtcLinkAddData(rtc_link_state,        // HIPRTC link state
                  input_type,            // type of the input data or bitcode
                  bit_code_ptr,          // input data which is null terminated
                  bit_code_size,         // size of the input data
                  "a",                   // optional name for this input
                  0,                     // size of the options
                  0,                     // Array of options applied to this input
                  0);                    // Array of option values cast to void*

hiprtcLinkAddFile(rtc_link_state,        // HIPRTC link state
                  input_type,            // type of the input data or bitcode
                  bc_file_path.c_str(),  // path to the input file where bitcode is present
                  0,                     // size of the options
                  0,                     // Array of options applied to this input
                  0);                    // Array of option values cast to void*

Once the bitcodes for multiple architectures are added to the link instance, the linking of the device code must be completed using hiprtcLinkComplete() which generates the final binary.

hiprtcLinkComplete(rtc_link_state,       // HIPRTC link state
                   &binary,              // upon success, points to the output binary
                   &binarySize);         // size of the binary is stored (optional)

If the hiprtcLinkComplete() returns successfully, the generated binary can be loaded and run using the hipModule* APIs.

hipModuleLoadData(&module, binary);

Note

Input Types#

HIPRTC provides hiprtcJITInputType enumeration type which defines the input types accepted by the Linker APIs. Here are the enum values of hiprtcJITInputType. However only the input types HIPRTC_JIT_INPUT_LLVM_BITCODE, HIPRTC_JIT_INPUT_LLVM_BUNDLED_BITCODE and HIPRTC_JIT_INPUT_LLVM_ARCHIVES_OF_BUNDLED_BITCODE are supported currently.

HIPRTC_JIT_INPUT_LLVM_BITCODE can be used to load both LLVM bitcode or LLVM IR assembly code. However, HIPRTC_JIT_INPUT_LLVM_BUNDLED_BITCODE and HIPRTC_JIT_INPUT_LLVM_ARCHIVES_OF_BUNDLED_BITCODE are only for bundled bitcode and archive of bundled bitcode.

HIPRTC_JIT_INPUT_CUBIN = 0,
HIPRTC_JIT_INPUT_PTX,
HIPRTC_JIT_INPUT_FATBINARY,
HIPRTC_JIT_INPUT_OBJECT,
HIPRTC_JIT_INPUT_LIBRARY,
HIPRTC_JIT_INPUT_NVVM,
HIPRTC_JIT_NUM_LEGACY_INPUT_TYPES,
HIPRTC_JIT_INPUT_LLVM_BITCODE = 100,
HIPRTC_JIT_INPUT_LLVM_BUNDLED_BITCODE = 101,
HIPRTC_JIT_INPUT_LLVM_ARCHIVES_OF_BUNDLED_BITCODE = 102,
HIPRTC_JIT_NUM_INPUT_TYPES = (HIPRTC_JIT_NUM_LEGACY_INPUT_TYPES + 3)

Backward Compatibility of LLVM Bitcode/IR#

For HIP applications utilizing HIPRTC to compile LLVM bitcode/IR, compatibility is assured only when the ROCm or HIP SDK version used for generating the LLVM bitcode/IR matches the version used during the runtime compilation. When an application requires the ingestion of bitcode/IR not derived from the currently installed AMD compiler, it must run with HIPRTC and comgr dynamic libraries that are compatible with the version of the bitcode/IR.

Comgr is a shared library that incorporates the LLVM/Clang compiler that HIPRTC relies on. To identify the bitcode/IR version that comgr is compatible with, one can execute “clang -v” using the clang binary from the same ROCm or HIP SDK package. For instance, if compiling bitcode/IR version 14, the HIPRTC and comgr libraries released by AMD around mid 2022 would be the best choice, assuming the LLVM/Clang version included in the package is also version 14.

To ensure smooth operation and compatibility, an application may choose to ship the specific versions of HIPRTC and comgr dynamic libraries, or it may opt to clearly specify the version requirements and dependencies. This approach guarantees that the application can correctly compile the specified version of bitcode/IR.

Error Handling#

HIPRTC defines the hiprtcResult enumeration type and a function hiprtcGetErrorString() for API call error handling. hiprtcResult enum defines the API result codes. HIPRTC APIs return hiprtcResult to indicate the call result. hiprtcGetErrorString() function returns a string describing the given hiprtcResult code, for example HIPRTC_SUCCESS to “HIPRTC_SUCCESS”. For unrecognized enumeration values, it returns “Invalid HIPRTC error code”.

hiprtcResult enum supported values and the hiprtcGetErrorString() usage are mentioned below.

HIPRTC_SUCCESS = 0,
HIPRTC_ERROR_OUT_OF_MEMORY = 1,
HIPRTC_ERROR_PROGRAM_CREATION_FAILURE = 2,
HIPRTC_ERROR_INVALID_INPUT = 3,
HIPRTC_ERROR_INVALID_PROGRAM = 4,
HIPRTC_ERROR_INVALID_OPTION = 5,
HIPRTC_ERROR_COMPILATION = 6,
HIPRTC_ERROR_LINKING = 7,
HIPRTC_ERROR_BUILTIN_OPERATION_FAILURE = 8,
HIPRTC_ERROR_NO_NAME_EXPRESSIONS_AFTER_COMPILATION = 9,
HIPRTC_ERROR_NO_LOWERED_NAMES_BEFORE_COMPILATION = 10,
HIPRTC_ERROR_NAME_EXPRESSION_NOT_VALID = 11,
HIPRTC_ERROR_INTERNAL_ERROR = 12

hiprtcResult result;
result = hiprtcCompileProgram(prog, 1, opts);
if (result != HIPRTC_SUCCESS) {
std::cout << "hiprtcCompileProgram fails with error " << hiprtcGetErrorString(result);
}

HIPRTC General APIs#

HIPRTC provides hiprtcVersion(int* major, int* minor) for querying the version. This sets the output parameters major and minor with the HIP Runtime compilation major version and minor version number respectively.

Currently, it returns hardcoded values. This should be implemented to return HIP runtime major and minor version in the future releases.

Lowered Names (Mangled Names)#

HIPRTC mangles the __global__ function names and names of __device__ and __constant__ variables. If the generated binary is being loaded using the HIP Runtime API, the kernel function or __device__/__constant__ variable must be looked up by name, but this is very hard when the name has been mangled. To overcome this, HIPRTC provides API functions that map __global__ function or __device__/__constant__ variable names in the source to the mangled names present in the generated binary.

The two APIs hiprtcAddNameExpression() and hiprtcGetLoweredName() provide this functionality. First, a ‘name expression’ string denoting the address for the __global__ function or __device__/__constant__ variable is provided to hiprtcAddNameExpression(). Then, the program is compiled with hiprtcCreateProgram(). During compilation, HIPRTC will parse the name expression string as a C++ constant expression at the end of the user program. Finally, the function hiprtcGetLoweredName() is called with the original name expression and it returns a pointer to the lowered name. The lowered name can be used to refer to the kernel or variable in the HIP Runtime API.

Note

Example#

Kernel containing various definitions __global__ functions/function templates and __device__/__constant__ variables can be stored in a string.

static constexpr const char gpu_program[] {
R"(
__device__ int V1; // set from host code
static __global__ void f1(int *result) { *result = V1 + 10; }
namespace N1 {
namespace N2 {
__constant__ int V2; // set from host code
__global__ void f2(int *result) { *result = V2 + 20; }
}
}
template<typename T>
__global__ void f3(int *result) { *result = sizeof(T); }
)"};

hiprtcAddNameExpression() is called with various name expressions referring to the address of __global__ functions and __device__/__constant__ variables.

kernel_name_vec.push_back("&f1");
kernel_name_vec.push_back("N1::N2::f2");
kernel_name_vec.push_back("f3<int>");
for (auto&& x : kernel_name_vec) hiprtcAddNameExpression(prog, x.c_str());
variable_name_vec.push_back("&V1");
variable_name_vec.push_back("&N1::N2::V2");
for (auto&& x : variable_name_vec) hiprtcAddNameExpression(prog, x.c_str());

After which, the program is compiled using hiprtcCompileProgram(), the generated binary is loaded using hipModuleLoadData(), and the mangled names can be fetched using hirtcGetLoweredName().

for (decltype(variable_name_vec.size()) i = 0; i != variable_name_vec.size(); ++i) {
  const char* name;
  hiprtcGetLoweredName(prog, variable_name_vec[i].c_str(), &name);
}

for (decltype(kernel_name_vec.size()) i = 0; i != kernel_name_vec.size(); ++i) {
  const char* name;
  hiprtcGetLoweredName(prog, kernel_name_vec[i].c_str(), &name);
}

The mangled name of the variables are used to look up the variable in the module and update its value.

hipDeviceptr_t variable_addr;
size_t bytes{};
hipModuleGetGlobal(&variable_addr, &bytes, module, name);
hipMemcpyHtoD(variable_addr, &initial_value, sizeof(initial_value));

Finally, the mangled name of the kernel is used to launch it using the hipModule APIs.

hipFunction_t kernel;
hipModuleGetFunction(&kernel, module, name);
hipModuleLaunchKernel(kernel, 1, 1, 1, 1, 1, 1, 0, nullptr, nullptr, config);

Versioning#

HIPRTC uses the following versioning:

  • Linux

    • HIPRTC follows the same versioning as HIP runtime library.

    • The so name field for the shared library is set to MAJOR version. For example, for HIP 5.3 the so name is set to 5 (hiprtc.so.5).

  • Windows

    • HIPRTC dll is named as hiprtcXXYY.dll where XX is MAJOR version and YY is MINOR version. For example, for HIP 5.3 the name is hiprtc0503.dll.

HIP header support#

Added HIPRTC support for all the hip common header files such as library_types.h, hip_math_constants.h, hip_complex.h, math_functions.h, surface_types.h etc. from 6.1. HIPRTC users need not include any HIP macros or constants explicitly in their header files. All of these should get included via HIPRTC builtins when the app links to HIPRTC library.

Deprecation notice#

  • Currently HIPRTC APIs are separated from HIP APIs and HIPRTC is available as a separate library libhiprtc.so/ libhiprtc.dll. But on Linux, HIPRTC symbols are also present in libamdhip64.so in order to support the existing applications. Gradually, these symbols will be removed from HIP library and applications using HIPRTC will be required to explicitly link to HIPRTC library. However, on Windows hiprtc.dll must be used as the amdhip64.dll doesn’t contain the HIPRTC symbols.

  • Data types such as uint32_t, uint64_t, int32_t, int64_t defined in std namespace in HIPRTC are deprecated earlier and are being removed from ROCm release 6.1 since these can conflict with the standard C++ data types. These data types are now prefixed with __hip__, for example __hip_uint32_t. Applications previously using std::uint32_t or similar types can use __hip_ prefixed types to avoid conflicts with standard std namespace or application can have their own definitions for these types. Also, type_traits templates previously defined in std namespace are moved to __hip_internal namespace as implementation details.