Ahead of Time Compilation

Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference

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ID 767253

Date 9/08/2022

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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:

No additional compilation time is done when running your application.
No just-in-time (JIT) bugs encountered due to compilation for the target device, because this step is skipped with AOT compilation.
Your final code, executing on the target device, can be tested as-is before you deliver it to end-users.

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.

To manually update your version of OCLOC, refer to Upgrade OpenCL™ Offline Compiler (OCLOC).

AOT Compilation Supported Options

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

-fsycl-targets, to specify the device target
-Xs, to pass options to the backend tool

-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:

-fsycl-targets=spir64_x86_64

-Xs "-march=<arch>", where <arch> is one of the following:

Switch	Display Name
`avx`	Intel® Advanced Vector Extensions (Intel® AVX)
`avx2`	Intel® Advanced Vector Extensions 2 (Intel® AVX2)
`avx512`	Intel® Advanced Vector Extensions 512 (Intel® AVX-512)
`sse4.2`	Intel® Streaming SIMD Extensions 4.2 (Intel® SSE4.2)

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

Linux

icpx -fsycl -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" main.cpp

Windows

icx -fsycl /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

```
icpx -fsycl -c main.cpp
```

icpx -fsycl -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp main.o

Windows

```
icx -fsycl -c /EHsc main.cpp
```

icx -fsycl /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

icpx -fsycl -c -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp

icpx -fsycl main.cpp mandel.o -fsycl-targets=spir64_x86_64 -Xs "-march=avx2"

Windows

icx -fsycl -c /EHsc -fsycl-targets=spir64_x86_64 -Xs "-march=avx2" mandel.cpp

icx -fsycl /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:

-fsycl-targets=spir64_gen

-Xs "-device <arch>" option, where <arch> is the target device. Possible values:

Switch	Display Name
`skl`	6th generation Intel® Core™ processor (Skylake with Intel® Processor Graphics Gen9)
`kbl`	7th generation Intel® Core™ processor (Kaby Lake with Intel® Processor Graphics Gen9)
`cfl`	8th generation Intel® Core™ processor (Coffee Lake with Intel® Processor Graphics Gen9)
`glk`	Gemini Lake with Intel® Processor Graphics Gen9
`icllp`	10th generation Intel® Core™ processor (Ice Lake with Intel® Processor Graphics Gen11)
`tgllp`	11th generation Intel® Core™ processor (Tiger Lake with Intel® Processor Graphics Gen12)
`dg1`	Intel® Iris® X^e MAX graphics
`Gen9`	Intel® Processor Graphics Gen9
`Gen11`	Intel® Processor Graphics Gen11
`Gen12LP`	Intel® Processor Graphics Gen12 (Lower Power)
`adls`	12th generation Intel® Core™ processor (Alder Lake S with Intel® Processor Graphics Gen12.2)
`aldp`	12th generation Intel® Core™ processor (Alder Lake P with Intel® Processor Graphics Gen12.2)

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

To compile for a single target, using skl as an example, use:

icpx -fsycl -fsycl-targets=spir64_gen -Xs "-device skl" vector-add.cpp

To compile for two targets, using skl and icllp as examples, use:

icpx -fsycl -fsycl-targets=spir64_gen -Xs "-device skl,icllp" vector-add.cpp

To compile for all the targets known to OCLOC, use:

icpx -fsycl -fsycl-targets=spir64_gen -Xs "-device *" vector-add.cpp

Windows

To compile for a single target, using skl as an example, use:

icx -fsycl /EHsc -fsycl-targets=spir64_gen -Xs "-device skl" vector-add.cpp

To compile for two targets, using skl and icllp as examples, use:

icx -fsycl /EHsc -fsycl-targets=spir64_gen -Xs "-device skl,icllp" vector-add.cpp

To compile for all the targets known to OCLOC, use:

icx -fsycl /EHsc -fsycl-targets=spir64_gen -Xs "-device *" vector-add.cpp

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

```
icpx -fsycl -c main.cpp
```

icpx -fsycl -fsycl-targets=spir64_gen -Xs "-device *" mandel.cpp main.o

Windows

```
icx -fsycl -c /EHsc main.cpp
```

icx -fsycl /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

icpx -fsycl -c -fsycl-targets=spir64_gen mandel.cpp

icpx -fsycl main.cpp mandel.o -fsycl-targets=spir64_gen -Xs "-device *"

Windows

icx -fsycl -c /EHsc -fsycl-targets=spir64_gen mandel.cpp

icx -fsycl /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:

To compile, in the dialog box, select: Configuration Properties > DPC++ > General > Specify SYCL offloading targets for AOT compilation
To link, in the dialog box, select: Configuration Properties > Linker > General > Specify CPU Target Device for AOT compilation

GPU:

To compile, in the dialog box, select: Configuration Properties > DPC++ > General > Specify SYCL offloading targets for AOT compilation
To link, in the dialog box, select: Configuration Properties > Linker > General > Specify GPU Target Device for AOT compilation

Parent topic: Compilation

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Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference

Ahead of Time Compilation

Prerequisites

AOT Compilation Supported Options

Use AOT for the Target Device (Intel® CPUs)

Use AOT for Integrated Graphics (Intel® GPU)

Use AOT in Microsoft Visual Studio

See Also