Setting Optimization Level

Option

Description

Default

-O, -O1,

IA-32 compiler: Optimize to favor code size. Disable option -fp.  -O1 disables intrinsics inlining to reduce code size.

Itanium(TM) compiler: Optimize to favor code size. Enable the same optimizations as -O2 except for loop unrolling. -O1 turns off software pipelining to reduce code size.

Generally, -O2 is recommended over -O1.

OFF

-O2

Optimizes for speed, but disables some optimizations that increase code size for a small speed benefit. Default.

-O2

-O3
 

Enables -O2 option with more aggressive optimization and sets high-level optimizations, including loop transformation, OpenMP, and prefetching. High-level optimizations use the properties of source code constructs such as loops and arrays in applications written in high-level programming languages.
Optimizes for maximum speed, but may not improve performance for some programs.

OFF

-O0

Disables optimizations -O1, -O2 and -O3.

OFF