Intel® 64 and IA-32 Architectures Optimization Reference Manual

CODING FOR SIMD ARCHITECTURES4.3.1 Coding MethodologiesSoftware developers need to compare the performance improvement that can beobtained from assembly code versus the cost of those improvements. Programmingdirectly in assembly language for a target platform may produce the required performancegain, however, assembly code is not portable between processor architecturesand is expensive to write and maintain.Performance objectives can be met by taking advantage of the different SIMD technologiesusing high-level languages as well as assembly. The new C/C++ languageextensions designed specifically for SSSE3, SSE3, SSE2, SSE, and MMX technologyhelp make this possible.Figure 4-2 illustrates the trade-offs involved in the performance of hand-codedassembly versus the ease of programming and portability.PerformanceAssemblyInstrinsicsC/C++/FortranAutomaticVectorizationEase of Programming/PortabilityFigure 4-2. Hand-Coded Assembly and High-Level Compiler Performance Trade-offsThe examples that follow illustrate the use of coding adjustments to enable the algorithmto benefit from the SSE. The same techniques may be used for single-precisionfloating-point, double-precision floating-point, and integer data under SSSE3, SSE3,SSE2, SSE, and MMX technology.4-8