GCC standard optimizations behavior

Question

Here I compile an input program with -O2 optimization level (with gcc 4.8.4) and measure the execution time:

gcc -O2 -c test.c -o obj.o
TIMEFORMAT=\'%3R\' &a         


        

Answer 1

There is 2 good optimization that should be know:

• -O2: Optimize space and time (caution: does not initialize variable)
• -Os: Optimize space and time (caution: does not initialize variable)