Merge pull request #7879 from retronym/classtag-cache

Share instance of ClassTag in a ClassValue based cache
scala · Jul 17, 2019 · b5029ab · b5029ab
2 parents c50ca9a + 9f7866c
commit b5029ab
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Showing 4 changed files with 50 additions and 22 deletions.
diff --git a/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala b/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
@@ -157,13 +157,12 @@ trait StdAttachments {
    *  typechecks to be a macro application. Then we need to unmark it, expand it and try to treat
    *  its expansion as a macro impl reference.
    */
-  def unmarkMacroImplRef(tree: Tree): Tree = tree.removeAttachment[MacroImplRefAttachment.type](MacroImplRefAttachmentTag)
+  def unmarkMacroImplRef(tree: Tree): Tree = tree.removeAttachment[MacroImplRefAttachment.type]
 
   /** Determines whether a tree should or should not be adapted,
    *  because someone has put MacroImplRefAttachment on it.
    */
-  def isMacroImplRef(tree: Tree): Boolean = tree.hasAttachment[MacroImplRefAttachment.type](MacroImplRefAttachmentTag)
-  private[this] val MacroImplRefAttachmentTag: reflect.ClassTag[MacroImplRefAttachment.type] = reflect.classTag[MacroImplRefAttachment.type]
+  def isMacroImplRef(tree: Tree): Boolean = tree.hasAttachment[MacroImplRefAttachment.type]
 
   /** Since mkInvoke, the applyDynamic/selectDynamic/etc desugarer, is disconnected
    *  from typedNamedApply, the applyDynamicNamed argument rewriter, the latter
@@ -176,9 +175,8 @@ trait StdAttachments {
    */
   case object DynamicRewriteAttachment
   def markDynamicRewrite(tree: Tree): Tree = tree.updateAttachment(DynamicRewriteAttachment)
-  def unmarkDynamicRewrite(tree: Tree): Tree = tree.removeAttachment[DynamicRewriteAttachment.type](DynamicRewriteAttachmentTag)
-  def isDynamicRewrite(tree: Tree): Boolean = tree.attachments.get[DynamicRewriteAttachment.type](DynamicRewriteAttachmentTag).isDefined
-  private[this] val DynamicRewriteAttachmentTag: reflect.ClassTag[DynamicRewriteAttachment.type] = reflect.classTag[DynamicRewriteAttachment.type]
+  def unmarkDynamicRewrite(tree: Tree): Tree = tree.removeAttachment[DynamicRewriteAttachment.type]
+  def isDynamicRewrite(tree: Tree): Boolean = tree.attachments.get[DynamicRewriteAttachment.type].isDefined
 
   /**
    * Marks a tree that has been adapted by typer and sets the original tree that was in place before.

diff --git a/src/library/scala/reflect/ClassTag.scala b/src/library/scala/reflect/ClassTag.scala
@@ -121,29 +121,38 @@ object ClassTag {
   val Nothing : ClassTag[scala.Nothing]    = Manifest.Nothing
   val Null    : ClassTag[scala.Null]       = Manifest.Null
 
+  private[this] val cache = new ClassValue[ClassTag[_]] {
+    override def computeValue(runtimeClass: jClass[_]): ClassTag[_] = {
+      runtimeClass match {
+        case x if x.isPrimitive => primitiveClassTag(runtimeClass)
+        case ObjectTYPE         => ClassTag.Object
+        case NothingTYPE        => ClassTag.Nothing
+        case NullTYPE           => ClassTag.Null
+        case _                  => new GenericClassTag[AnyRef](runtimeClass)
+      }
+    }
+
+    private def primitiveClassTag[T](runtimeClass: Class[_]): ClassTag[_] = runtimeClass match {
+      case java.lang.Byte.TYPE      => ClassTag.Byte
+      case java.lang.Short.TYPE     => ClassTag.Short
+      case java.lang.Character.TYPE => ClassTag.Char
+      case java.lang.Integer.TYPE   => ClassTag.Int
+      case java.lang.Long.TYPE      => ClassTag.Long
+      case java.lang.Float.TYPE     => ClassTag.Float
+      case java.lang.Double.TYPE    => ClassTag.Double
+      case java.lang.Boolean.TYPE   => ClassTag.Boolean
+      case java.lang.Void.TYPE      => ClassTag.Unit
+    }
+  }
+
   @SerialVersionUID(1L)
   private class GenericClassTag[T](val runtimeClass: jClass[_]) extends ClassTag[T] {
     override def newArray(len: Int): Array[T] = {
       java.lang.reflect.Array.newInstance(runtimeClass, len).asInstanceOf[Array[T]]
     }
   }
 
-  def apply[T](runtimeClass1: jClass[_]): ClassTag[T] =
-    runtimeClass1 match {
-      case java.lang.Byte.TYPE      => ClassTag.Byte.asInstanceOf[ClassTag[T]]
-      case java.lang.Short.TYPE     => ClassTag.Short.asInstanceOf[ClassTag[T]]
-      case java.lang.Character.TYPE => ClassTag.Char.asInstanceOf[ClassTag[T]]
-      case java.lang.Integer.TYPE   => ClassTag.Int.asInstanceOf[ClassTag[T]]
-      case java.lang.Long.TYPE      => ClassTag.Long.asInstanceOf[ClassTag[T]]
-      case java.lang.Float.TYPE     => ClassTag.Float.asInstanceOf[ClassTag[T]]
-      case java.lang.Double.TYPE    => ClassTag.Double.asInstanceOf[ClassTag[T]]
-      case java.lang.Boolean.TYPE   => ClassTag.Boolean.asInstanceOf[ClassTag[T]]
-      case java.lang.Void.TYPE      => ClassTag.Unit.asInstanceOf[ClassTag[T]]
-      case ObjectTYPE               => ClassTag.Object.asInstanceOf[ClassTag[T]]
-      case NothingTYPE              => ClassTag.Nothing.asInstanceOf[ClassTag[T]]
-      case NullTYPE                 => ClassTag.Null.asInstanceOf[ClassTag[T]]
-      case _                        => new GenericClassTag[T](runtimeClass1)
-    }
+  def apply[T](runtimeClass1: jClass[_]): ClassTag[T] = cache.get(runtimeClass1).asInstanceOf[ClassTag[T]]
 
   def unapply[T](ctag: ClassTag[T]): Option[Class[_]] = Some(ctag.runtimeClass)
 }
diff --git a/test/benchmarks/src/main/scala/scala/reflect/ClassTagBenchmark.scala b/test/benchmarks/src/main/scala/scala/reflect/ClassTagBenchmark.scala
@@ -25,6 +25,7 @@ class ClassTagBenchmark {
   var refClassTag: ClassTag[_] = null
   var otherValue: Object = null
   var arraySize: Int = 100
+  private[this] var refClasses: Array[Class[_]] = _
 
   @Setup def setup(): Unit = {
     unitClassTag = classTag[Unit]
@@ -38,6 +39,7 @@ class ClassTagBenchmark {
     doubleClassTag = classTag[Double]
     refClassTag = classTag[ClassTagBenchmark]
     otherValue = new Object
+    refClasses = Array(classOf[java.lang.Boolean], classOf[java.lang.Character], classOf[java.lang.Short], classOf[java.lang.Integer], classOf[java.lang.Long], classOf[java.lang.Float], classOf[java.lang.Double])
   }
 
   @Benchmark def primitivesNegOnRefClassTag(bh: Blackhole): Any = {
@@ -86,6 +88,15 @@ class ClassTagBenchmark {
 
   @Benchmark def refClassTagUnapplyNeg2Direct(bh: Blackhole): Any = unapplyDirect(refClassTag, otherValue)
 
+  @Benchmark def lookupClassTag(bh: Blackhole): Any = {
+    var clss = refClasses
+    var i = 0
+    while (i < clss.length) {
+      bh.consume(ClassTag.apply(clss(i)))
+      i += 1
+    }
+  }
+
   def unapplyDirect(ct: ClassTag[_], x: AnyRef): Option[_] = {
     if (null != x && (ct.runtimeClass.isInstance(x))) Some(x)
     else None

diff --git a/test/files/run/classtags-cached.scala b/test/files/run/classtags-cached.scala
@@ -0,0 +1,10 @@
+import reflect.ClassTag
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(implicitly[ClassTag[SomeClass]] eq implicitly[ClassTag[SomeClass]])
+    assert(implicitly[ClassTag[Array[SomeClass]]] eq implicitly[ClassTag[Array[SomeClass]]])
+  }
+}
+
+class SomeClass