4.1.3 /optimize, /o, (/optimize=5)

The /optimize qualifier sets the base optimization and code analysis level, ranging from 0 (no optimization) to 5 (maximum optimization). The optimization level can also be modified on a loop-by-loop basis by the C*$* optimize (<integer>) directive. Some of the code analysis techniques can be enabled with the /scalaropt qualifier.

The meaning of each of the different optimization levels is as follows. Each optimization level is cumulative, for example, level 4 performs what is listed below for that level, in addition to what is listed for levels 0-3.

• 0 - KAP performs no loop optimization.

• 1 - KAP performs only simple analysis and optimization. Induction variables are recognized. DO loop interchanging techniques are applied.

• 2 - Lifetime analysis is performed to determine when last-value assignment of subprogram-local scalar variables is necessary. More powerful data dependence tests are used.

• 3 - More loop interchanging is attempted, such as interchanging of triangular loops. Special-case data dependence tests are used. Special index sets called wraparound variables are recognized.

• 4 - Loop interchanging around reductions is attempted. More exact data dependence tests are used.

• 5 - Array expansion is enabled at this point.

A higher optimization level results in more optimization, more analysis, and more ambitious transformations, along with increased compilation time.