Ahead of Time Compilation

Ahead of Time (AOT) Compilation is a helpful feature for your development lifecycle or distribution time. It benefits you when you know beforehand what your target device is going to be at application execution time. The AOT feature provides the following benefits:

A program built with AOT compilation for a specific target device will not run on a non-specific device. You must detect the proper target device at runtime and report an error if the targeted device is not present. The use of exception handling with an asynchronous exception handler is recommended.

SYCL supports AOT compilation for the following targets: Intel® CPUs, Intel® Processor Graphics (Gen9 or above), and Intel® FPGA.

Prerequisites

To target a GPU with the AOT feature, you must have the OpenCL™ Offline Compiler (OCLOC) tool installed. OCLOC can generate binaries that use OpenCL™ or the Intel® oneAPI Level Zero (Level Zero) backend.

Linux

OCLOC is not packaged with the Linux version of Intel® oneAPI DPC++/C++ Compiler and must be installed separately. Refer to Install OpenCL™ Offline Compiler (OCLOC) for details.

Windows

OCLOC is packaged with the Windows version of Intel® oneAPI DPC++/C++ Compiler.

AOT Compilation Supported Options

Use the following options to target a specific device for AOT compilation:

-Xs is a general device target option. If there are multiple targets desired (example: -fsycl-targets=spir64_gen,spir64_x86_64) the options specified with -Xs apply to all targets. This is not desired for multiple targets. You can use -Xsycl-target-backend=spir64_gen <option> and -Xsycl-target-backend=spir64_x86_64 <option> to add specificity.

When using Ahead of Time (AOT) compilation, the options passed with -Xs are not compiler options.

To see a list of the options you can pass with -Xs when using AOT, specify -fsycl-help=gen, -fsycl-help=x86_64, or -fsycl-help=fpga on the command line.

Use AOT for the Target Device (Intel® CPUs)

Use the following option arguments to specify Intel® CPUs as the target device for AOT compilation:

The following examples tell the compiler to generate code that uses Intel® AVX2 instructions:

Linux

dpcpp -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" main.cpp
Windows
dpcpp-cl /EHsc -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" main.cpp

Build an Application with Multiple Source Files for CPU Targeting

Method 1: Compile your normal files (with no SYCL kernels) to create host objects. Then compile the file with the kernel code and link it with the rest of the application.

Linux

  1. dpcpp -c main.cpp
  2. dpcpp -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp main.o 
Windows
  1. dpcpp-cl -c /EHsc main.cpp
  2. dpcpp-cl /EHsc -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp main.obj

Method 2: Compile the file with the kernel code and create a fat object. Then compile the rest of the files and linking to create a fat executable:

Note

Currently, Method 2 only works on a HOST selector.

Linux

  1. dpcpp -c -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp
  2. dpcpp main.cpp mandel.o -fsycl-targets=spir64_x86_64 -Xs "-march=avx2"
Windows
  1. dpcpp-cl -c /EHsc -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp 
  2. dpcpp-cl /EHsc main.cpp mandel.obj -fsycl-targets=spir64_x86_64 -Xs "-march=avx2"

Use AOT for Integrated Graphics (Intel® GPU)

Use the following option arguments to specify Intel® GPU as the target device for AOT compilation:

To see the complete list of supported target device types for your installed version of OCLOC, run:

ocloc compile --help

If multiple target devices are listed in the compile command, the Intel® oneAPI DPC++/C++ Compiler compiles for each of these targets and creates a fat-binary that contains all the device binaries produced this way.

Examples of supported -device patterns:

Linux

Windows

Build an Application with Multiple Source Files for GPU Targeting

Method 1: Compile your normal files (with no SYCL kernels) to create host objects. Then compile the file with the kernel code and link it with the rest of the application.

Linux

  1. dpcpp -c main.cpp
  2. dpcpp -fsycl-targets=spir64_gen -Xs "-device *" mandel.cpp main.o
Windows
  1. dpcpp-cl -c /EHsc main.cpp
  2. dpcpp-cl /EHsc -fsycl-targets=spir64_gen -Xs "-device *" mandel.cpp main.obj

Method 2: Compile the file with the kernel code and create a fat object. Then compile the rest of the files and linking to create a fat executable:

Note

Currently, Method 2 only works on a HOST selector.

Linux

  1. dpcpp -c -fsycl-targets=spir64_gen mandel.cpp
  2. dpcpp main.cpp mandel.o -fsycl-targets=spir64_gen -Xs "-device *"
Windows
  1. dpcpp-cl -c /EHsc -fsycl-targets=spir64_gen mandel.cpp 
  2. dpcpp-cl /EHsc main.cpp mandel.obj -fsycl-targets=spir64_gen -Xs "-device *"

Use AOT in Microsoft Visual Studio

You can use Microsoft Visual Studio for compiling and linking. Set the following flags to use AOT compilation for CPU or GPU:

CPU:

GPU:

See Also