-fast

This single option selects a number of performance options that, working together, produce object code optimized for execution speed without an excessive increase in compilation time.

The options selected by -fast are subject to change from one release to another, and not all are available on each platform:

• -native generates code optimized for the host architecture.

• -O4 sets optimization level.

• -libmil inlines calls to some simple library functions.

• -fsimple=1 simplifies floating-point code (SPARC only).

• -dalign uses faster, double word loads and stores (SPARC only).

• -xlibmopt use optimized libm math library (SPARC only).

• -fns -ftrap=%none turns off all trapping.

• -depend analyze loops for data dependencies (SPARC only).

• -nofstore disables forcing precision on expressions (x86 only).

-fast provides a quick way to engage much of the optimizing power of the compilers. Each of the composite options may be specified individually, and each may have side effects to be aware of (discussed in the Fortran User's Guide). Following -fast with additional options adds further optimizations. For example:

f77 -fast -O5 ...

sets the optimization to level 5 instead of 4.

-fast includes -dalign and -native. These options may have unexpected side effects for some programs.