Effects of Compiler Optimization (-O3 -O2 -O1 -O0) on code

[Tassadaq Cheema]

-O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function.

-O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify -O2. As compared to -O, this option increases both compilation time and the performance of the generated code.

-O3 Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions, -funswitch-loops, -fpredictive-commoning, -fgcse-after-reload and -ftree-vectorize options.

-O0 Reduce compilation time and make debugging produce the expected results. This is the default.

-Os Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size.

[shaddisi23]

Optimizing accumulation takes somewhat added time, and a lot added amnesics for a ample function.

-O2 Optimize even more. GCC performs about all accurate optimizations that do not absorb a space-speed tradeoff. The compiler does not accomplish bend unrolling or action in lining if you specify -O2. As compared to -O, this advantage increases both accumulation time and the achievement of the generated code.

-O3 Optimize yet more. -O3 turns on all optimizations defined by -O2 and as well turns on the -finline functions, -fun witch-loops, -fpredictive-commoning, -focused-after-reload and -free-vectorize options.