On Sat, Apr 21, 2007 at 02:19:28AM +0200, Zdenek Dvorak wrote: > Hello, > > > Steve Ellcey wrote: > > > > >This seems unfortunate. I was hoping I might be able to turn on loop > > >unrolling for IA64 at -O2 to improve performance. I have only started > > >looking into this idea but it seems to help performance quite a bit, > > >though it is also increasing size quite a bit too so it may need some > > >modification of the unrolling parameters to make it practical. > > > > To me it is obvious that optimizations are target dependent. For > > instance loop unrolling is really a totally different optimization > > on the ia64 as a result of the rotating registers. > > that we do not use. Nevertheless, there are still compelling reasons > for why unrolling is more useful on ia64 then on other architectures > (importance of scheduling, insensitivity to code size growth). > > Another option would be to consider enabling (e.g.) -funroll-loops > -fprefetch-loop-arrays by default on -O3. I think it is fairly rare > for these flags to cause performance regressions (although of course > more measurements to support this claim would be necessary).
-fprefetch-loop-arrays shouldn't be on by default since HW prefetch usually will have negative performance impact on Intel. H.J.
