performance - What does the 'optimise' scala compiler flag do? -



performance - What does the 'optimise' scala compiler flag do? -

i've tried using scalac -optimise version 2.7.7. @ time never got performance improvements, compilation took longer.

is situation improve in scala 2.9.0 ? optimisations covered flag ?

strange, there similar question on scala-user group:

rex kerr answered @ time (may):

i have never found case production code sped using -optimise, @ to the lowest degree when using sun jvm. grant in cases happen, seems apply similar optimizations jvm already. perhaps if there limits on optimization depth, using -optimise remove few layers , allow jvm few more. don't bother testing more, given how many cases (dozens) i've tried runtime hasn't changed measurably.

i expect have impact on vms more conservative (e.g. jrockit) or less sophisticated (e.g. dalvik).

ismael juma added:

the scala distribution compiled -optimise, indeed it's not on unless argument passed scalac.

is not mature enough, or lead bugs, changed semantic, etc ?

as far understand, team decided conservative , enable scala distribution initial step (in scala 2.8.0). maybe it's thought consider extending in next major release.

for influence of '-optimise' (amongst other factors) in scala2.9, see scala-language thread called "scala2.9 slower?".

i'm bit concerned. after seeing -optimize optimize "for comprehensions" on 2.9.0, benchmarked code, , discovered 2.5 times slower 2.8.1.

the results leave a... mixed feeling.

performance scala compiler-construction compiler-optimization

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