Development Reference Guides

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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
.

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
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:
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:
  • -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:
    dpcpp -fsycl-targets=spir64_gen -Xs "-device skl" vector-add.cpp
  • To compile for two targets, using
    skl
    and
    icllp
    as examples, use:
    dpcpp -fsycl-targets=spir64_gen -Xs "-device skl,icllp" vector-add.cpp
  • To compile for all the targets known to OCLOC, use:
    dpcpp -fsycl-targets=spir64_gen -Xs "-device *" vector-add.cpp
Windows
  • To compile for a single target, using
    skl
    as an example, use:
    dpcpp-cl /EHsc -fsycl-targets=spir64_gen -Xs "-device skl" vector-add.cpp
  • To compile for two targets, using
    skl
    and
    icllp
    as examples, use:
    dpcpp-cl /EHsc -fsycl-targets=spir64_gen -Xs "-device skl,icllp" vector-add.cpp
  • To compile for all the targets known to OCLOC, use:
    dpcpp-cl /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
  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:
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:
  • 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

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.