Intel C++ Compiler

Intel C++ Compiler (also known as icc or icl) describes a group of C/C++ compilers from Intel. Compilers are available for Linux, Microsoft Windows and Mac OS X. Manufacturer suggested retail prices start at US$ 399.

Intel supports compilation for its IA-32, Intel 64, Itanium 2, and XScale processors. The Intel C++ Compiler for x86 and Intel 64 features an automatic vectorizer that can generate SSE, SSE2, and SSE3 SIMD instructions, the embedded variant for Intel Wireless MMX and MMX 2. Since its introduction, the Intel C++ Compiler for IA-32 has greatly increased adoption of SSE2 in Windows application development.

Intel C++ Compiler further supports both OpenMP and automatic parallelization for symmetric multiprocessing. With the add-on product Cluster OpenMP, the compiler can also automatically generate Message Passing Interface calls for distributed memory multiprocessing from OpenMP directives.

Intel C++ Compiler belongs to the family of compilers with the Edison Design Group frontend (like the SGI MIPSpro, Comeau C++, Portland Group, and others). The compiler is also notable for being widely used for SPEC CPU Benchmarks of IA-32, x86-64, and Itanium 2 architectures.

Optimizations

Intel tunes its compilers to optimize for its hardware platforms to minimize stalls and to produce code that executes in the smallest number of cycles. The Intel C++ Compiler supports three separate high-level techniques for optimizing the compiled program interprocedural optimization (IPO), Profile-Guided Optimization (PGO), and High Level Optimizations (HLO).

Profile-Guided Optimization refers to a mode of optimization where the compiler is able to access data from a sample run of the program across a representative input set. The data would indicate which areas of the program are executed more frequently, and which areas are executed less frequently. All optimizations benefit from profile-guided feedback because they are less reliant on heuristics when making compilation decisions.

High Level Optimizations are optimizations performed on a version of the program that more closely represents the source code. High level optimizations include loop interchange, loop fusion, loop unrolling, loop distribution, data prefetch, and more. High level optimizations are usually very aggressive and may take considerable compilation time.

Interprocedural Optimization applies typical compiler optimizations (such as constant propagation) but using a broader scope that may include multiple procedures, multiple files, or the entire program.

Languages

Intel's suite of compilers has front ends for C, C++, and for Fortran.

Early versions of ICC for Linux that predate GCC 3.x use the Dinkumware name mangling scheme, in order to provide a more standard implementation of C++ than GCC 2.x. However, this makes its ABI incompatible with both GCC versions.

Architectures

• IA-32
• x86-64 (Intel 64 and AMD64)
• IA-64 i.e. the "Itanium"
• XScale

Versions

The following versions of Intel C++ Compiler have been released as of November 2007:

Compiler version	Release date	Major New Features
Intel C++ Compiler 10.1	Nov 7 2007	New OpenMP* compatibility runtime library: if you use the new OpenMP RTL, you can mix and match with libraries and objects built by Visual C++. To use the new libraries, you need to use the new option "-Qopenmp /Qopenmp-lib:compat" on Windows, and "-openmp -openmp-lib:compat" on Linux. This version of the Intel compiler supports more intrinsics from Visual Studio 2005. VS2008 support - command line only right now. The IDE integration is not supported yet.
Intel C++ Compiler 10.0	June 5 2007	Improved parallelizer and vectorizer, Streaming SIMD Extensions 4 (SSE4), new and enhanced optimization reports for advanced loop transformations, new optimized exception handling implementation.
Intel C++ Compiler 9.0	June 14 2005	AMD64 architecture (for Windows), software-based speculative pre-computation (SSP) optimization, improved loop optimization reports.
Intel C++ Compiler 8.1	?	AMD64 architecture (for Linux).
Intel C++ Compiler 8.0	December 15 2003	Precompiled headers, code-coverage tools. [1]
Intel C++ Compiler 7.1	?	Partial support for the Intel Pentium 4 with Streaming SIMD Extensions 3 (SSE3). [2]
Intel C++ Compiler 7.0	November 25 2002	[3]
Intel C++ Compiler 6.0	April 24 2002	[4]

Experimental / Prototype Versions

In addition, the following "prototype" editions have been made available:

Compiler version	Release date	Major New Features
Intel STM Compiler Prototype Edition	September 17 2007	Prototype version of the Intel compiler that implements support for Software Transactional Memory (STM). The Intel STM Compiler supports Linux and Windows, producing 32 bit code for x86 (Intel and AMD) processors. Intel stated the belief that "The availability of such a prototype compiler allows unprecedented exploration by C / C++ software developers of a promising technique to make programming for multi-core easier." The STM compiler requires that you already have the Intel compiler installed.

Structure

Like many modern optimizing compilers, the Intel compiler has a front end, an optimizing middle, and code-generating back ends.

Flags and manuals

Windows	Linux	Comment
/Od	-O0	No optimization
/O1	-O1	Optimize for size
/O2	-O2	Optimize for speed and enable some optimization
/O3	-O3	Enable all optimizations as O2, and intensive loop optimizations
/fast	-fast	Shorthand. On windows equates to "/O3 /Qipo /xT /no-prec-div" on Linux "-O3 -ipo -static -xT -no-prec-div". Note that the processor specific optimizations (-xT) will change with new compiler versions. Useful if you want to compile your program for release.
/Qprof_gen	-prof_gen	Compile the program and instrument it for a profile generating run.
/Qprof_use	-prof_use	May only be used after running a program that was previously compiled using prof_gen. Uses profile information during each step of the compilation process.

Debugging

The Intel compiler provides debugging information that is standard for the common debuggers (DWARF 2 on Linux, similar to gdb, and COFF for Windows). The flags to compile with debugging information are /Zi on Windows and -g on Linux.

Intel also provides its own debugger called idb, which can be run in both dbx and gdb compatible command mode.

While the Intel compiler can generate a gprof compatible profiling output, Intel also provides a kernel level, system-wide statistical profiler as a separate product called VTune. VTune features an easy-to-use GUI (integrated into Visual Studio for Windows, Eclipse for Linux) as well as a command line interface.

External links

• Intel Compilers