Vectorization

The vectorizer speeds up your code by automatically generating Single-Instruction Multiple-Data (SIMD) code for qualifying loops. These SIMD instructions can be found on processors employing Intel® MMX™ technology, Streaming SIMD Extensions (SSE), and Streaming SIMD Extensions 2 (SSE2) of the Pentium® 4 processor.

The vectorizer can also use the Short Vector Math library.

For a detailed discussion of MMX technology, SSE and SSE2, see the following pages at the Intel Software College:

• MMX™ Technology
• Streaming SIMD Extensions (SSE)
• Streaming SIMD Extensions 2 (SSE2)

In order to take advantage of the vectorizer, a loop must meet the following criteria:

• iteration independence
• memory disambiguation—All memory references within the loop are unique.
• high loop count

To enable the vectorizer, use the following options (shown previously):

• Windows*: -Qax[K|W|N|B|P] or -Qx[K|W|N|B|P]
• Linux*: -x[K|W|N|B|P] or -ax[K|W||N|B|P]

For detailed information on the vectorizer, see the tutorial Optimizing Performance Using Intel's Vectorizing Compilers at the Intel Software College.