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

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Document Table of Contents
Document Table of Contents x
Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference
Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference x
Intel® oneAPI DPC++/C++ Compiler Introduction Compiler Setup Compiler Reference Compilation Optimization and Programming Compatibility and Portability Notices and Disclaimers
Intel® oneAPI DPC++/C++ Compiler Introduction x
Get Help and Support Related Information
Compiler Setup x
Use the Command Line Use Eclipse Use Microsoft Visual Studio
Use the Command Line x
Specify Component Locations Invoke the Compiler Use the Command Line on Windows File Extensions Use Makefiles for Compilation Use CMake with the Compiler Use Compiler Options Specify Compiler Files Convert Projects to Use a Selected Compiler
Use Eclipse x
Add the Compiler to Eclipse Multiversion Compiler Support Use Cheat Sheets Create a Simple Eclipse Project Makefiles Use Intel Libraries with Eclipse
Use Microsoft Visual Studio x
Create a New Project Use the Intel® oneAPI DPC++/C++ Compiler Select the Compiler Version Specify a Base Platform Toolset Use Property Pages Use Intel® Libraries with Microsoft Visual Studio* Include MPI Support Dialog Box Help
Dialog Box Help x
Options: Compilers dialog box Use Intel® oneAPI DPC++/C++ Compiler dialog box Options: Intel Libraries for oneAPI dialog box Options: Converter dialog box
Compiler Reference x
C/C++/SYCL Calling Conventions Compiler Options Floating-Point Operations Attributes Intrinsics Libraries Macros Pragmas Error Handling
Compiler Options x
Alphabetical Option List General Rules for Compiler Options What Appears in the Compiler Option Descriptions Optimization Options Code Generation Options Interprocedural Optimization Options Advanced Optimization Options Optimization Report Options Offload Compilation, OpenMP*, and Parallel Processing Options Floating-Point Options Inlining Options Output, Debug, and Precompiled Header Options Preprocessor Options Component Control Options Language Options Data Options Compiler Diagnostic Options Compatibility Options Linking or Linker Options Miscellaneous Options Deprecated and Removed Compiler Options Display Option Information Alternate Compiler Options Portability and GCC-compatible Warning Options
Optimization Options x
fast fbuiltin, Oi foptimize-sibling-calls GF nolib-inline O Od Ofast Os Ot Ox
Code Generation Options x
arch ax, Qax EH fasynchronous-unwind-tables fdata-sections, Gw fexceptions ffunction-sections, Gy fomit-frame-pointer Gd GR guard Gv m, Qm m64, Qm64 m80387 march masm mbranches-within-32B-boundaries, Qbranches-within-32B-boundaries mintrinsic-promote, Qintrinsic-promote momit-leaf-frame-pointer mtune, tune regcall, Qregcall x, Qx xHost, QxHost
Interprocedural Optimization Options x
flto ipo, Qipo
Advanced Optimization Options x
ffreestanding, Qfreestanding fjump-tables fvec-peel-loops, Qvec-peel-loops fvec-remainder-loops, Qvec-remainder-loops fvec-with-mask, Qvec-with-mask ipp-link, Qipp-link qactypes, Qactypes qdaal, Qdaal qipp, Qipp qmkl, Qmkl qmkl-ilp64, Qmkl-ilp64 qopt-assume-no-loop-carried-dep, Qopt-assume-no-loop-carried-dep qopt-dynamic-align, Qopt-dynamic-align qopt-for-throughput, Qopt-for-throughput qopt-multiple-gather-scatter-by-shuffles, Qopt-multiple-gather-scatter-by-shuffles qopt-streaming-stores, Qopt-streaming-stores qtbb, Qtbb unroll, Qunroll use-intel-optimized-headers, Quse-intel-optimized-headers vec, Qvec vec-threshold, Qvec-threshold
Optimization Report Options x
qopt-report, Qopt-report qopt-report-file, Qopt-report-file
Offload Compilation, OpenMP*, and Parallel Processing Options x
device-math-lib fintelfpga fiopenmp, Qiopenmp fno-sycl-libspirv foffload-static-lib fopenmp fopenmp-declare-target-scalar-defaultmap, Qopenmp-declare-target-scalar-defaultmap fopenmp-device-lib fopenmp-target-buffers, Qopenmp-target-buffers fopenmp-targets, Qopenmp-targets fsycl fsycl-add-targets fsycl-dead-args-optimization fsycl-device-code-split fsycl-device-lib fsycl-device-only fsycl-early-optimizations fsycl-enable-function-pointers fsycl-esimd-force-stateless-mem fsycl-explicit-simd fsycl-force-target fsycl-help fsycl-host-compiler fsycl-host-compiler-options fsycl-id-queries-fit-in-int fsycl-instrument-device-code fsycl-link fsycl-link-huge-device-code fsycl-link-targets fsycl-max-parallel-link-jobs fsycl-targets fsycl-unnamed-lambda fsycl-use-bitcode nolibsycl qopenmp, Qopenmp qopenmp-lib, Qopenmp-lib qopenmp-link qopenmp-simd, Qopenmp-simd qopenmp-stubs, Qopenmp-stubs reuse-exe Wno-sycl-strict Xopenmp-target Xs Xsycl-target
Floating-Point Options x
ffp-contract fimf-absolute-error, Qimf-absolute-error fimf-accuracy-bits, Qimf-accuracy-bits fimf-arch-consistency, Qimf-arch-consistency fimf-domain-exclusion, Qimf-domain-exclusion fimf-force-dynamic-target, Qimf-force-dynamic-target fimf-max-error, Qimf-max-error fimf-precision, Qimf-precision fimf-use-svml, Qimf-use-svml fma, Qfma fp-model, fp fp-speculation, Qfp-speculation pc, Qpc
Inlining Options x
fgnu89-inline finline finline-functions
Output, Debug, and Precompiled Header Options x
c debug (Linux*) debug (Windows*) Fa fasm-blocks FD Fe Fo Fp ftrapuv, Qtrapuv fverbose-asm g gdwarf grecord-gcc-switches gsplit-dwarf o RTC S use-msasm Y- Yc Yu Zi, Z7, ZI
Preprocessor Options x
B C D dD, QdD dM, QdM E EP FI H, QH I I- idirafter imacros iprefix iquote isystem iwithprefix iwithprefixbefore Kc++, TP M, QM MD, QMD MF, QMF MG, QMG MM, QMM MMD, QMMD MQ MT, QMT nostdinc++ P pragma-optimization-level U undef X
Component Control Options x
Qoption
Language Options x
ansi fno-gnu-keywords fno-operator-names fno-rtti fpermissive fshort-enums fsyntax-only funsigned-char J std, Qstd strict-ansi vd vmg x (type option) Zc Zg Zp Zs
Data Options x
fcommon fkeep-static-consts, Qkeep-static-consts fmath-errno fpack-struct fpic fpie fstack-protector fstack-security-check fvisibility fzero-initialized-in-bss, Qzero-initialized-in-bss GA Gs GS mcmodel Qlong-double
Compiler Diagnostic Options x
w w, W Wabi Wall Wcheck-unicode-security Wcomment Wdeprecated Weffc++, Qeffc++ Werror, WX Werror-all Wextra-tokens Wformat Wformat-security Wmain Wmissing-declarations Wmissing-prototypes Wpointer-arith Wreorder Wreturn-type Wshadow Wsign-compare Wstrict-aliasing Wstrict-prototypes Wtrigraphs Wuninitialized Wunknown-pragmas Wunused-function Wunused-variable Wwrite-strings
Compatibility Options x
gcc-toolchain vmv
Linking or Linker Options x
Bdynamic Bstatic Bsymbolic Bsymbolic-functions dynamic-linker F (Windows*) fixed Fm fuse-ld l L LD link MD MT no-libgcc nodefaultlibs no-intel-lib, Qno-intel-lib nostartfiles nostdlib pie pthread shared shared-intel shared-libgcc static static-intel static-libgcc static-libstdc++ T u (Linux*) v Wa Wl Wp Xlinker Zl
Miscellaneous Options x
dryrun dumpmachine dumpversion help nologo save-temps, Qsave-temps showIncludes sox, Qsox sysroot Tc TC Tp version watch
Floating-Point Operations x
Programming Tradeoffs in Floating-Point Applications Use the -fp-model, /fp Option Denormal Numbers Set the FTZ and DAZ Flags Tuning Performance IEEE Floating-Point Operations
Attributes x
align align_value allow_cpu_features concurrency_safe const cpu_dispatch, cpu_specific mpx target
Libraries x
Create Libraries Use Intel Shared Libraries on Linux Manage Libraries Redistribute Libraries When Deploying Applications Resolve References to Shared Libraries Intel's Memory Allocator Library SIMD Data Layout Templates Intel® C++ Class Libraries Intel's C++ Asynchronous I/O Extensions for Windows IEEE 754-2008 Binary Floating-Point Conformance Library Intel's Numeric String Conversion Library
SIMD Data Layout Templates x
Function Calls and Containers User-Level Interface Examples
Function Calls and Containers x
Construct an n_container Bounds
User-Level Interface x
SDLT Primitives soa1d_container aos1d_container n_container Bounds Accessors Proxy Objects Number Representation Indexes Convenience and Correctness
aos1d_container x
access_by
n_container x
Layouts Shape make_ n_container template function extent_d template function
Shape x
n_extent_generator
Bounds x
bounds_t sdlt::bounds Template Function n_bounds_t n_bounds_generator bounds_d Template Function
Accessors x
soa1d_container::accessor and aos1d_container::accessor soa1d_container::const_accessor and aos1d_container::const_accessor Accessor Concept
Proxy Objects x
Proxy ConstProxy
Number Representation x
aligned_offset fixed_offset
Indexes x
linear_index n_index_t n_index_generator index_d template function
Convenience and Correctness x
max_val min_val
Examples x
Efficiency with Structure of Arrays Example Complex SDLT Primitive Construction Example Forward Dependency Example Use of Offsets and Methods on a SDLT Primitive Example RGB to YUV Conversion Example
Intel® C++ Class Libraries x
C++ Classes and SIMD Operations Capabilities of C++ SIMD Classes Integer Vector Classes Floating-Point Vector Classes Classes Quick Reference Programming Example Intel's valarray Implementation
Integer Vector Classes x
Terms and Syntax Rules for Operators Assignment Operator Logical Operators Addition and Subtraction Operators Multiplication Operators Shift Operators Comparison Operators Conditional Select Operators Debug Operations Unpack Operators Pack Operators Clear MMX™ State Operator Integer Functions for Intel® Streaming SIMD Extensions Conversions between Fvec and Ivec
Floating-Point Vector Classes x
Fvec Syntax and Notation Data Alignment Conversions Constructors and Initialization Arithmetic Operators Minimum and Maximum Operators Logical Operators Compare Operators Conditional Select Operators for Fvec Classes Cacheability Support Operators Debug Operations Load and Store Operators Unpack Operators Move Mask Operators
Intel's C++ Asynchronous I/O Extensions for Windows x
Intel's C++ Asynchronous I/O Library for Windows Intel's C++ Asynchronous I/O Class for Windows
Intel's C++ Asynchronous I/O Library for Windows x
<span class='option'>aio_read</span> <span class='option'>aio_write</span> Example for aio_read and aio_write Functions <span class='option'>aio_suspend</span> Example for aio_suspend Function <span class='option'>aio_error</span> <span class='option'>aio_return</span> Example for aio_error and aio_return Functions <span class='option'>aio_fsync</span> <span class='option'>aio_cancel</span> Example for aio_cancel Function <span class='option'>lio_listio</span> Example for lio_listio Function Asynchronous I/O Function Errors
Intel's C++ Asynchronous I/O Class for Windows x
Template Class async_class <span class='option'>get_last_operation_id</span> wait get_status get_last_error <span class='option'>get_error_operation_id</span> stop_queue resume_queue clear_queue Example for Using async_class Template Class
IEEE 754-2008 Binary Floating-Point Conformance Library x
Intel® IEEE 754-2008 Binary Floating-Point Conformance Library and Usage Function List Homogeneous General-Computational Operations Functions <i></i>General-Computational Operations Functions Quiet-Computational Operations Functions Signaling-Computational Operations Functions Non-Computational Operations Functions
Intel's Numeric String Conversion Library x
Use Intel's Numeric String Conversion Library Function List
Macros x
ISO Standard Predefined Macros Additional Predefined Macros Use Predefined Macros to Specify Intel® Compilers
Pragmas x
Intel-Specific Pragma Reference Intel-Supported Pragma Reference
Intel-Specific Pragma Reference x
block_loop/noblock_loop distribute_point inline, noinline, forceinline ivdep loop_count nofusion novector omp target variant dispatch ompx prefetch data prefetch/noprefetch unroll/nounroll unroll_and_jam/nounroll_and_jam vector
Compilation x
Compilation Overview Supported Environment Variables Pass Options to the Linker Specify Alternate Tools and Paths Use Configuration Files Use Response Files Global Symbols and Visibility Attributes for Linux* Save Compiler Information in Your Executable Link Debug Information Ahead of Time Compilation Device Offload Compilation Considerations Use a Third-Party Compiler as a Host Compiler for SYCL Code
Optimization and Programming x
Extensions OpenMP* Support Intel® oneAPI Level Zero Vectorization High-Level Optimization Interprocedural Optimization Methods to Optimize Code Size Disable or Decrease the Amount of Inlining Strip Symbols from Your Binaries Dynamically Link Intel-provided Libraries Exclude Unused Code and Data from the Executable Disable Recognition and Expansion of Intrinsic Functions Optimize Exception Handling Data Disable Loop Unrolling Disable Automatic Vectorization Avoid References to Compiler-specific Libraries Use Interprocedural Optimization Intel® oneAPI DPC++/C++ Compiler Math Library
OpenMP* Support x
Add OpenMP* Support Parallel Processing Model Worksharing Using OpenMP* Control Thread Allocation OpenMP* Pragmas OpenMP* Library Support OpenMP* Advanced Issues OpenMP* Implementation-Defined Behaviors OpenMP* Examples
OpenMP* Library Support x
OpenMP* Runtime Library Routines Intel® Compiler Extension Routines to OpenMP* OpenMP* Support Libraries Use the OpenMP Libraries Thread Affinity Interface OpenMP* Memory Spaces and Allocators
Intel® oneAPI Level Zero x
Intel® oneAPI Level Zero Switch Intel® oneAPI Level Zero Backend Specification Programming with the Intel® oneAPI Level Zero Backend
Vectorization x
Automatic Vectorization Explicit Vector Programming
Automatic Vectorization x
Vectorization Programming Guidelines Use Automatic Vectorization Vectorization and Loops Loop Constructs
Explicit Vector Programming x
User-Mandated or SIMD Vectorization SIMD-Enabled Functions SIMD-Enabled Function Pointers Vectorize a Loop Using the _Simd Keyword Function Annotations and the SIMD Directive for Vectorization Explicit SIMD SYCL Extension
Interprocedural Optimization x
Use Interprocedural Optimization Performance and Large Program Considerations Create a Library from IPO Objects Inline Expansion of Functions
Intel® oneAPI DPC++/C++ Compiler Math Library x
Use the Intel® oneAPI DPC++/C++ Compiler Math Library Math Function List Trigonometric Functions Hyperbolic Functions Exponential Functions Special Functions Nearest Integer Functions Remainder Functions Miscellaneous Functions Complex Functions C99 Macros
Compatibility and Portability x
Standards Conformance GCC Compatibility and Interoperability Microsoft Compatibility Port from Microsoft Visual C++* to the Intel® oneAPI DPC++/C++ Compiler Port from GCC* to the Intel® oneAPI DPC++/C++ Compiler
Port from Microsoft Visual C++* to the Intel® oneAPI DPC++/C++ Compiler x
Modify Your makefile Other Considerations
Port from GCC* to the Intel® oneAPI DPC++/C++ Compiler x
Modify Your makefiledpc Other Considerations
Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference

Methods to Optimize Code Size

This section provides some guidance on how to achieve smaller object and smaller executable size when using the optimizing features of Intel compilers.

There are two compiler options that are designed to prioritize code size over performance:

Option Result Notes

Os

Favors size over speed

This option enables optimizations that do not increase code size; it produces smaller code size than option O2.

Option Os disables some optimizations that may increase code size for a small speed benefit.

O1

Minimizes code size

Compared to option Os, option O1 disables even more optimizations that are generally known to increase code size. Specifying option O1 implies option Os.

As an intermediate step in reducing code size, you can replace option O3 with option O2 before specifying option O1.

Option O1 may improve performance for applications with very large code size, many branches, and execution time not dominated by code within loops.

For more information about compiler options mentioned in this topic, see their full descriptions in the Compiler Reference.

The rest of this topic briefly discusses other methods that may help you further improve code size even when compared to the default behaviors of options Os and O1.

Things to remember:

  • Some of these methods may already be applied by default when options Os and O1 are specified. All the methods mentioned in this topic can be applied at higher optimization levels.

  • Some of the options referred to in this topic will not necessarily cause code size reduction, and they may provide varying results (good, bad, or neutral) based on the characteristics of the target code. Still, these are the recommended things to try to see if they cause your binaries to become smaller while maintaining acceptable performance.

Disable or Decrease the Amount of Inlining

Inlining replaces a call to a function with the body of the function. This lets the compiler optimize the code for the inlined function in the context of its caller, usually yielding more specialized and better performing code. This also removes the overhead of calling the function at runtime.

However, replacing a call to a function by the code for that function usually increases code size. The code size increase can be substantial. To eliminate this code size increase, at the cost of the potential performance improvement, inlining can be disabled.

  • Advantage: Disabling or reducing this optimization can reduce code size.
  • Disadvantage: Performance is likely to be sacrificed by disabling or reducing inlining especially for applications with many small functions.

Use options:

Linux

fno-inline

Windows

Ob0

Strip Symbols from Your Binaries

You can specify a compiler option to omit debugging and symbol information from the executable without sacrificing its operability.

  • Advantage: This method noticeably reduces the size of the binary.
  • Disadvantage: It may be very difficult to debug a stripped application.

Use options:

Linux

Wl, --strip-all

Windows

None

Dynamically Link Intel-provided Libraries

By default, some of the Intel support and performance libraries are linked statically into an executable. As a result, the library codes are linked into every executable being built. This means that codes are duplicated.

It may be more profitable to link them dynamically.

  • Advantage: Performance of the resulting executable is normally not significantly affected. Library codes that are otherwise linked in statically into every executable will not contribute to the code size of each executable with this option. These codes will be shared between all executables using them, and they will be available independent of those executables.
  • Disadvantage: The libraries on which the resulting executable depends must be re-distributed with the executable for it to work properly. When libraries are linked statically, only library content that is actually used is linked into the executable. Dynamic libraries contain all the library content. Therefore, it may not be beneficial to use this option if you only need to build and/or distribute a single executable. The executable itself may be much smaller when linked dynamically, compared to a statically linked executable. However, the total size of the executable plus shared libraries or DLLs may be much larger than the size of the statically linked executable.

Use Options:

Linux

shared-intel

Windows

MD

NOTE:
Option MD affects all libraries, not only the Intel-provided ones.

Exclude Unused Code and Data from the Executable

Programs often contain dead code or data that is not used during their execution. Even if no expensive whole-program inter-procedural analysis is made at compile time to identify dead code, there are compiler options you can specify to eliminate unused functions and data at link time.

This method is often referred to as function-level or data-level linking.

  • Advantage: Only the code that is referenced remains in an executable. Dead functions and data are stripped from the executable. For the options passed to the linker, they also enable the linker to reorder the sections for other possible optimization.
  • Disadvantage: The object codes may become slightly larger because each function or datum is put into a separate section. The overhead is eliminated at the linking stage. This method requires linker support to strip unused sections and may increase linking time.

Use Options:

Linux

-fdata-sections -ffunction-sections -Wl,--gc-sections

Windows

/Gw /Gy /link /OPT:REF

NOTE:
Option MD affects all libraries, not only the Intel-provided ones.

These options (from the use options example above) are passed to the linker:

Linux

Wl, --gc-sections

Windows

link /OPT:REF

Disable Recognition and Expansion of Intrinsic Functions

When recognized, intrinsic functions can get expanded inline or their faster implementation in a library may be assumed and linked in. By default, Inline expansion of intrinsic functions is enabled.

In some cases, disabling this behavior may noticeably improve the size of the produced object or binary.

  • Advantage: Both the size of the object files and the size of library codes brought into an executable can be reduced.
  • Disadvantage: This method can prevent various performance optimizations from happening. Slower standard library implementation will be used. The size of the final executable can be increased in cases when code pulled in statically from a library for an otherwise inlined intrinsic is large.

Use Options:

Linux

fno-builtin

Windows

Oi-

Additional information:

  • This option is already the default if you specify option O1.

  • For C++, you can specify Linux option nolib-inline to disable inline expansion of standard library or intrinsic functions.

  • Depending on code characteristics, this option can sometimes increase binary size.

Optimize Exception Handling Data

For SYCL, enabling and disabling of exception handling is supported for host compilation.

If a program requires support for exception handling, the compiler creates a special section containing DWARF directives that are used by the Linux runtime to unwind and catch an exception.

This information is found in the .eh_frame section and may be shrunk using the compiler options listed below.

  • Advantage:

    These options may shrink the size of the object or binary file by up to 15%, though the amount of the reduction depends on the target platform. These options control whether unwind information is precise at an instruction boundary or at a call boundary. For example, option fno-asynchronous-unwind-tables can be used for programs that may only throw or catch exceptions.

  • Disadvantage: Both options may change the program's behavior. Do not use option fno-exceptions for programs that require standard C++ handling for objects of classes with destructors. Do not use option fno-asynchronous-unwind-tables for functions compiled with option -fexceptions that contain calls to other functions that might throw exceptions or for C++ functions that declare objects with destructors.

Use Options:

Linux

fno-exceptions or fno-asynchronous-unwind-tables

Windows

None

Read the compiler option descriptions, which explain what the defaults and behavior are for each target platform.

Disable Loop Unrolling

Unrolling a loop increases the size of the loop proportionally to the unroll factor.

Disabling (or limiting) this optimization may help reduce code size at the expense of performance.

  • Advantage: Code size is reduced.
  • Disadvantage: Performance of otherwise unrolled loops may noticeably degrade because this limits other possible loop optimizations.

Use Options:

Linux

unroll=0

Windows

Qunroll:0

NOTE:
This Windows option is not available for SYCL.

Additional information:

This option is already the default if you specify option Os or option O1.

Disable Automatic Vectorization

The compiler finds possibilities to use SIMD (Intel® Streaming SIMD Extensions (Intel® SSE)/Intel® Advanced Vector Extensions (Intel® AVX)) instructions to improve performance of applications. This optimization is called automatic vectorization.

In most cases, this optimization involves transformation of loops and increases code size, in some cases significantly.

Disabling this optimization may help reduce code size at the expense of performance.

  • Advantage: Compile-time is also improved significantly.
  • Disadvantage: Performance of otherwise vectorized loops may suffer significantly. If you care about the performance of your application, you should use this option selectively to suppress vectorization on everything except performance-critical parts.

Use Options:

Linux

no-vec

Windows

Qvec-

Additional information:

Depending on code characteristics, this option can sometimes increase binary size.

Avoid References to Compiler-specific Libraries

While compiler-specific libraries are intended to improve the performance of your application, they increase the size of your binaries.

Certain compiler options may improve the code size.

  • Advantage: The compiler will not assume the presence of compiler-specific libraries. It will generate only calls that appear in the source code.
  • Disadvantage: This method may sacrifice performance if the library codes were in hotspots. Also, because we cannot assume any libraries, some compiler optimizations will be suppressed.

Use Options:

Linux

ffreestanding

Windows

Qfreestanding-

NOTE:
This Windows option is not available for SYCL.

Additional information:

  • This option implies option fno-builtin. You can override that default by explicitly specifying option fbuiltin.

  • Depending on code characteristics, this option can sometimes increase binary size.

Use Interprocedural Optimization

Using interprocedural optimization (IPO) may reduce code size. It enables dead code elimination and suppresses generation of code for functions that are always inlined or proven that they are never to be called during execution.

  • Advantage: Depending on the code characteristics, this optimization can reduce executable size and improve performance.
  • Disadvantage: Binary size can increase depending on code/application..

Use Options:

Linux

ipo

Windows

Qipo

NOTE:
This method is not recommended if you plan to ship object files as part of a final product.
Parent topic: Optimization and Programming
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