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SI-6726 Hash consing for Pattern matching Sym-s

For the test case: https://issues.scala-lang.org/browse/SI-6726?focusedCommentId=61207&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-61207

time scalac -Ystatistics -Ystop-after:patmat sandbox/gen.scala

Before:

    real    1m47.737s
    user    2m14.314s
    sys 0m2.783s

After:

    real    1m23.574s
    user    1m51.795s
    sys 0m2.634s
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commit 14d8c222aa5f810fea34d35dc5f50d7f17ddc091 1 parent 32c0a2e
Jason Zaugg retronym authored adriaanm committed
19 src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
@@ -1897,17 +1897,24 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
1897 1897 case object False extends Prop
1898 1898
1899 1899 // symbols are propositions
1900   - case class Sym(val variable: Var, val const: Const) extends Prop {
1901   - private[this] val id = nextSymId
  1900 + abstract case class Sym(val variable: Var, val const: Const) extends Prop {
  1901 + private[this] val id = Sym.nextSymId
  1902 +
1902 1903 override def toString = variable +"="+ const +"#"+ id
1903 1904 }
1904   - private def nextSymId = {_symId += 1; _symId}; private var _symId = 0
1905   -
  1905 + class UniqueSym(variable: Var, const: Const) extends Sym(variable, const)
  1906 + object Sym {
  1907 + private var uniques: util.HashSet[Sym] = new util.HashSet("uniques", 512)
  1908 + def apply(variable: Var, const: Const): Sym = {
  1909 + val newSym = new UniqueSym(variable, const)
  1910 + (uniques findEntryOrUpdate newSym)
  1911 + }
  1912 + private def nextSymId = {_symId += 1; _symId}; private var _symId = 0
  1913 + }
1906 1914
1907 1915 def /\(props: Iterable[Prop]) = if (props.isEmpty) True else props.reduceLeft(And(_, _))
1908 1916 def \/(props: Iterable[Prop]) = if (props.isEmpty) False else props.reduceLeft(Or(_, _))
1909 1917
1910   -
1911 1918 trait PropTraverser {
1912 1919 def apply(x: Prop): Unit = x match {
1913 1920 case And(a, b) => apply(a); apply(b)
@@ -2167,7 +2174,7 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
2167 2174 class Lit(val sym: Sym, val pos: Boolean) {
2168 2175 override def toString = if (!pos) "-"+ sym.toString else sym.toString
2169 2176 override def equals(o: Any) = o match {
2170   - case o: Lit => (o.sym == sym) && (o.pos == pos)
  2177 + case o: Lit => (o.sym eq sym) && (o.pos == pos)
2171 2178 case _ => false
2172 2179 }
2173 2180 override def hashCode = sym.hashCode + pos.hashCode
3  src/reflect/scala/reflect/api/Symbols.scala
@@ -351,7 +351,8 @@ trait Symbols { self: Universe =>
351 351 def asFreeType: FreeTypeSymbol = throw new ScalaReflectionException(s"$this is not a free type")
352 352
353 353 /** @group Constructors */
354   - def newTermSymbol(name: TermName, pos: Position = NoPosition, flags: FlagSet = NoFlags): TermSymbol
  354 + def
  355 + newTermSymbol(name: TermName, pos: Position = NoPosition, flags: FlagSet = NoFlags): TermSymbol
355 356 /** @group Constructors */
356 357 def newModuleAndClassSymbol(name: Name, pos: Position = NoPosition, flags: FlagSet = NoFlags): (ModuleSymbol, ClassSymbol)
357 358 /** @group Constructors */

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