Enabling Aggressive Optimizations

To enable aggressive optimizations at the second, third, or fourth optimization levels, use the +Oaggressive option as follows:

cc +O2 +Oaggressive sourcefile.c

or:

cc +O3 +Oaggressive sourcefile.c

or:

cc +O4 +Oaggressive sourcefile.c

Aggressive optimizations are new optimizations or are optimizations that can change the behavior of programs. These optimizations may do any of the following:

convert certain library calls to millicode and inline instructions
cause the inlined routines strcpy(), sqrt(), fabs(), and alloca() to not return the routine's completion status in ERRNO
alter exception handling and asynchronous interrupt handling as a result of instruction scheduling optimization
cause less precise floating-point results
cause programs that perform comparisons between pointers to shared memory and pointers to private memory to run incorrectly

Use aggressive optimizations with stable, well-structured, ANSI-conforming code. These types of optimizations give you faster code, but are riskier than the default optimizations.

Enabling Aggressive Optimizations

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