.. _hpvm-comp-process:

HPVM Compilation Process
========================

Compilation of an HPVM program involves the following steps:


#. ``clang`` takes an HPVM-C/C++ program (e.g. ``main.c``) and produces an LLVM IR (``main.ll``) file that contains the HPVM-C function calls. The declarations of these functions are defined in ``test/benchmark/include/hpvm.h``, which must be included in the program.
#. ``opt`` takes (``main.ll``) and invoke the GenHPVM pass on it, which converts the HPVM-C function calls to HPVM intrinsics. This generates the HPVM textual representation (``main.hpvm.ll``).
#. ``opt`` takes the HPVM textual representation (``main.hpvm.ll``) and invokes the following passes in sequence: 

   * BuildDFG: Converts the textual representation to the internal HPVM representation.
   * LocalMem and DFG2LLVM_OpenCL: Invoked only when GPU target is selected. Generates the kernel module (``main.kernels.ll``) and the portion of the host code that invokes the kernel into the host module (``main.host.ll``).
   * DFG2LLVM_CPU: Generates either all, or the remainder of the host module (``main.host.ll``) depending on the chosen target.
   * ClearDFG: Deletes the internal HPVM representation from memory.

#. ``clang`` is used to to compile any remaining project files that would be later linked with the host module.
#. ``llvm-link`` takes the host module and all the other generate ``ll`` files, and links them with the HPVM runtime module (``hpvm-rt.bc``), to generate the linked host module (``main.host.linked.ll``). 
#. Generate the executable code from the generated ``ll`` files for all parts of the program:

   * GPU target: ``llvm-cbe`` takes the kernel module (``main.kernels.ll``) and generates an OpenCL representation of the kernels that will be invoked by the host.
   * CPU target: ``clang`` takes the linked  host module (``main.host.linked.ll``) and generates the CPU binary.