Hi I'm using an ARM thumb cross compiler for embedded systems and always do optimize for small size with -Os.
Though I've experimented with optimization flags, and loop unrolling. Normally loop unrolling is always bad for size, code is duplicated and size increases. Though I discovered that in some special cases where the number of iteration is very small, eg a loop of 2-3 times, in this case an unrolling could make code size smaller - eg. losen up registers used for index in loops etc. Example when I use the flag "-fpeel-loops" together with -Os I will 99% of the cases get smaller code size for ARM thumb target. Some my question is how unrolling works with -Os, is it always totally disabled, or are there some cases when it could be tested, eg. with small number iterations, so loop can be eliminated? Could eg. "-fpeel-loops" be enabled by default for -Os perhaps? Now its only enabled for -O2 and above I think. Thanks and Best Regards Fredrik
