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 stack unwind-based 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

Technical documentation

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