g 2b 2b optimization flags

1-O0			//optimization for compilation time (default)	
2-O1 or -O	//optimization for code size and execution time
3-O2			//optimization more for code size and execution time
4-O3			//optimization even more for code size and execution time
5-Os			//optimization for code size	
6-Ofast		//O3 with fast none accurate math calculations