Frequently Asked Questions
This page contains the most frequently asked questions about the
Intel® DPC++ Compatibility Tool.
General Information
How do I migrate source files that are using C++11 or newer C++ standard features
on Linux* and Windows*?
On Linux, the default C++ standard for the Intel® DPC++ Compatibility Tool’s
parser is C++98, with some C++11 features
accepted. If you want to enable other C++11 or newer standard
features in the Intel® DPC++ Compatibility Tool, you need to add
the
--extra-arg="-std=<value>"
option to the
command line. The supported values are:- c++11
- c++14
- c++17
On Windows, the default C++ standard for the Intel® DPC++ Compatibility Tool’s
parser is C++14. If you want to enable C++17
features in the Intel® DPC++ Compatibility Tool, you need to add
the option
--extra-arg="-std=c++17"
to the command line.How do I migrate files on Windows when using a CMake project?
For a CMake project on a Windows OS, you can use CMake to generate
Microsoft Visual Studio* project files (
vcxproj
files). Then choose one of
the following options:- Migrate the source files on the command line by using the--vcxprojfileoption of the Intel® DPC++ Compatibility Tool.
- Migrate the entire project in Microsoft Visual Studio with an Intel® DPC++ Compatibility Tool Microsoft Visual Studio plugin.
How is the migrated code formatted?
The Intel® DPC++ Compatibility Tool provides two options to control the format of
migrated code:
--format-range
and --format-style
.If input source code is well formatted, the Intel® DPC++ Compatibility Tool
will use default options settings
--format-range
and --format-style
to format the resulting
code.If input source code is not well formatted (for example, the tool
detects mixed use of tabs and spaces or mixed indents) you can do
one of the following:
- The Intel® DPC++ Compatibility Tool will try to detect the indent size of the original code and apply it to the resulting code. You can guide the tool by settingTabWidthandUseTabin the.clang-formatfile. Because the input source code is not well formatted, the indents in the resulting code may still be inconsistent.
- Run the Intel® DPC++ Compatibility Tool with the--format-range=alloption to format the entire resulting file. The change between input source code and resulting source code may be large and make it more difficult to compare the code.
- Format your input source code, then use the Intel® DPC++ Compatibility Tool with the same.clang-formatfile for migration.
Why does the compilation database (compile_commands.json) not contain all
source file(s) in the project?
In the project build folder, the command
intercept-build make [target]
is
used to generate the compilation database. The content of the compilation
database depends on the optional [target] parameter. If you need to get the
list of files corresponding to default build target, do not specify the [target]
parameter.How do I use the migrated module file in the new project?
.cu
module files are compiled with the -ptx
or -cubin
options in the
original project and dynamically loaded into other *.cu
files with
cuModuleLoad()
or cuModuleLoadData()
.The Intel® DPC++ Compatibility Tool migrates module file code in the same way as other
*.cu
files. In addition, it adds a wrapper function for each function in the
module file that has the _global_
attribute.You can compile the migrated module file into a dynamic library and load the
library with a dynamic library API appropriate to your platform. For example:
- In Linux, load a dynamic library (.so) usingdlopen()
- In Windows, load a dynamic library (.dll) usingLoadLibraryA()
Is the memory space allocated by sycl::malloc_device, sycl::malloc_host, and dpct::dpct_malloc initialized?
The memory allocated by
sycl::malloc_device
, sycl::malloc_host
, and
dpct::dpct_malloc
is not initialized. If your program explicitly or
implicitly relies on the initial value of newly allocated memory, the program
may fail at runtime. Adjust your code to avoid such failures.For example, the following original code:
// original code
int *device_mem = nullptr;device_mem = sycl::malloc_device<int>(size, dpct::get_default_queue());
device_mem[0] += somevalue;
is adjusted to initialize the newly allocated memory to 0 before use:
// fixed DPC++ code
int *device_mem = nullptr;device_mem = sycl::malloc_device<int>(size, dpct::get_default_queue());
dpct::get_default_queue().memset(0, size).wait();
device_mem[0] += somevalue;
Troubleshooting
How do I fix an error such as “error: unknown type name” when I migrate files
with “dpct –in-root=srcdir –out-root=dstdir *.cu”?
The problem may be caused by files in the
*.cu
list, which can
be used as header files (included with an #include
statement)
and are not supposed to be parsed as a standalone file. In this
case, the Intel® DPC++ Compatibility Tool reports an error if it
cannot parse the file because the file depends on the
definitions/declarations in other files. Use one of the methods
below to migrate your content:- Rely on the Intel® DPC++ Compatibility Tool to decide which files to migrate with:compile_commands.json: “dpct -p=compile_commands.json --in-root=srcdir --out-root=dstdir”
- Manually pass specific files to migrate, but do not pass the files that are included in other files and not supposed to be compiled as a standalone file in the original application. The header files are migrated automatically when they are included by the files provided as the input to the tool and are located within thein-rootfolder:dpct --in-root= srcdir --out-root=dstdir sample.cu
How do I fix a parsing error such as “no member named ‘max’ in namespace ‘std’”
or “no member named ‘min’ in namespace ‘std’” when migrating code on Windows?
Use one of the following methods to resolve the error:
- Add#include <algorithm>to the source file before usingstd::minandstd::max
- Define the NOMINMAX macro by inserting#define NOMINMAXbefore includingWinDef.h
How do I fix a compilation error such as “error: dlopen not declared” when I
compile code on a Windows machine, that was originally migrated on Linux?
When the Intel® DPC++ Compatibility Tool generates the source code, it uses dynamic loading
APIs specific to the OS on which the Intel® DPC++ Compatibility Tool is running.
For example,
dlopen
, dlclose
, and dlsym
are used on Linux and
LoadLibraryA
, FreeLibrary
, and GetProcAddress
are used on Windows.If your code was migrated on a OS that is different from the OS you
need to compile the generated code on, migrate the project again with the
Intel® DPC++ Compatibility Tool on the target OS or fix the code manually.
Why didn’t the “atomic*” APIs get migrated?
The Intel® DPC++ Compatibility Tool may assume that the “atomic*” APIs are user-defined
APIs, in which case they are not migrated.
This can occur in the following scenarios:
- The CUDA include path is specified by both--cuda-include-pathand-I*, but the paths are different
- The CUDA include path is specified by-I*, but there are other CUDA include files located on the default CUDA install path
To make sure “atomic*” APIs are migrated, don’t use
-I*
to specify the CUDA
include path with the dpct
migration command. Instead, use only
--cuda-include-path
to specify the CUDA include path.Why did my migration fail with “error: restrict requires a pointer or reference”?
The C++ standard does not support the restrict qualifier and the C standard
supports the restrict qualifier only on pointers to an object type.
Based on these language standards the Intel® DPC++ Compatibility Tool emits the parsing error.
You may need to adjust the source code.
How do I resolve incorrect runtime behavior for dpct::dev_mgr and dpct:mem_mgr
in a library project that is loaded more than once in another application?
dpct::dev_mgr
and dpct::mem_mgr
are singleton classes in the
Intel® DPC++ Compatibility Tool helper functions. When the helper function headers are used
to build an executable project, both dpct::dev_mgr
and dpct::mem_mgr
will have only one instance in the executable. However, when the helper function
headers are used to build a library project and the library project is loaded
more than once with dlopen()
(or LoadLibraryA()
for Windows) in an
application, more than two instances of dpct::dev_mgr
and dpct::mem_mgr
will be created and result in incorrect runtime behavior.For example, both files
libA.cpp
and libB.cpp
include the Intel® DPC++ Compatibility Tool
helper function header dpct.hpp
, and they are built into dynamic libraries
libA.so
and libB.so
respectively. If an application main.cpp
imports
the libraries with dlopen()
, there will be two instances of dpct::dev_mgr
and dpct::mem_mgr
in the runtime of the application.To resolve this issue, separate the implementation and the declaration of
dpct::dev_mgr
and dpct::mem_mgr
in the Intel® DPC++ Compatibility Tool helper function:- Create a new C++ filedpct_helper.cpp.
- Move the implementation ofinstance()inclass dev_mgrfromdpct/device.hpptodpct_helper.cpp.For example, the originaldpct/device.hpp:class dev_mgr { public: static dev_mgr &instance() { // the implementation and the declaration of dev_mgr::instance static dev_mgr d_m; return d_m; } ... }is updated to:class dev_mgr { public: static dev_mgr &instance();//the declaration of dev_mgr::instance ... }and the newdpct_helper.cppnow contains the implementation ofdev_mgr::instance():#include <dpct/device.hpp> dpct::dev_mgr &dev_mgr::instance(){ // the implementation of dev_mgr::instance static dev_mgr d_m; return d_m; }
- Similar to step two, move the implementation ofinstance()in theclass mem_mgrfromdpct/memory.hpptodpct_helper.cpp.
- Builddpct_helper.cppinto a dynamic librarylibdpct_helper.
- In Linux:dpcpp -g -shared -o libdpct_helper.so -fPIC ./dpct_helper.cpp
- In Windows:cl.exe /LD dpct_helper.cpp
- Add librarylibdpct_helperto the environment variables.
- In Linux: Add the location oflibdpct_helper.sointoLD_LIBRARY_PATH.
- In Windows: Add the location oflibdpct_helper.dllintoPATH.
- Dynamically linklibdpct_helperwhen building libraries and applications.
After performing the update steps, all the libraries and applications will share
the same instance of the device manager
dpct::dev_mgr
and the memory manager
dpct::mem_mgr
in Intel® DPC++ Compatibility Tool helper functions.Why do I get “warning: shift count >= width of type” when I compile migrated
code with the Intel® oneAPI DPC++/C++ Compiler?
Shifting bits where the shift is greater than the type length is undefined
behavior for the Intel® oneAPI DPC++/C++ Compiler and may result in different behavior on
different devices. Adjust your code to avoid this type of shift.
For example, the migrated DPC++ code:
// migrated DPC++ code
void foo() {
...
unsigned int bit = index[tid] % 32;
unsigned int val = in[tid] << 32 - bit;
...
}
is adjusted to avoid a bit shift that is greater than the type length:
// fixed DPC++ code
void foo() {
...
unsigned int bit = index[tid] % 32;
unsigned int val;
if(32 - bit == 32)
val = 0;
else
val = in[tid] << 32 - bit;
...
}