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Avoid boxing FlagSets in union and allOf #3497

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Nov 20, 2017
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Avoid boxing FlagSets in union and allOf #3497

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20 changes: 16 additions & 4 deletions compiler/src/dotty/tools/dotc/core/Flags.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -172,12 +172,24 @@ object Flags {
}

/** The union of all flags in given flag set */
def union(flagss: FlagSet*) = (EmptyFlags /: flagss)(_ | _)
def union(flagss: FlagSet*): FlagSet = {
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This is still going to box, isn't it? FlagSet* becomes Seq[FlagSet], value classes in generic positions are always boxed.

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We avoid reboxing in the fold, half of the boxes are gone.

var flag = EmptyFlags
for (f <- flagss)
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If you want to go deep in micro-optimizations, you could use a while loop

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Should avoid FlagSet* altogether.

flag |= f
flag
}

/** The conjunction of all flags in given flag set */
def allOf(flags1: FlagSet, flags2: FlagSet): FlagConjunction = {
assert(flags1.numFlags == 1 && flags2.numFlags == 1, "Flags.allOf doesn't support flag " + (if (flags1.numFlags != 1) flags1 else flags2))
FlagConjunction((flags1 | flags2).bits)
}

/** The conjunction of all flags in given flag set */
def allOf(flagss: FlagSet*) = {
assert(flagss forall (_.numFlags == 1), "Flags.allOf doesn't support flag " + flagss.find(_.numFlags != 1))
FlagConjunction(union(flagss: _*).bits)
def allOf(flags1: FlagSet, flags2: FlagSet, flags3: FlagSet, flagss: FlagSet*): FlagConjunction = {
val flags0 = allOf(flags1, flags2) | flags3
assert(flags3.numFlags == 1 && flagss.forall(_.numFlags == 1), "Flags.allOf doesn't support flag " + (if (flags3.numFlags != 1) flags3 else flagss.find(_.numFlags != 1)))
FlagConjunction((flags0 | union(flagss: _*)).bits)
}

def commonFlags(flagss: FlagSet*) = union(flagss.map(_.toCommonFlags): _*)
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