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.
Right but we might in the future
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).
And large number of registers.
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).
Well unroll loops blows up code size, so it has to have positive
value, not merely no negative value :-)
Zdenek
