Vectorization Key Programming Guidelines

The goal of vectorizing compilers is to exploit single-instruction multiple data (SIMD) processing automatically. Users can help however by supplying the compiler with additional information; for example, directives. Review these guidelines and restrictions, see code examples in further topics, and check them against your code to eliminate ambiguities that prevent the compiler from achieving optimal vectorization.

You will often need to make some changes to your loops. Guidelines for loop bodies follow.



There are a number of restrictions that you should be aware of. Vectorization depends on the two major factors:

Many stylistic issues that prevent automatic vectorization by compilers are found in loop structures. The ambiguity arises from the complexity of the keywords, operators, data references, and memory operations within the loop bodies.

However, by understanding these limitations and by knowing how to interpret diagnostic messages, you can modify your program to overcome the known limitations and enable effective vectorization. The following sections summarize the capabilities and restrictions of the vectorizer with respect to loop structures.