`-funroll-loops'
Unroll loops whose number of iterations can be determined at
compile time or upon entry to the loop. `-funroll-loops' implies
both `-fstrength-reduce' and `-frerun-cse-after-loop'. This
option makes code larger, and may or may not make it run faster.
`-O3' turns on all optimizations specified by
`-O2' and also turns on the `-finline-functions', `-fweb',
`-funit-at-a-time', `-ftracer', `-funswitch-loops' and
`-frename-registers' options.