Don't use runtime reflection from the batch compiler.

Not only does this save a big chunk of time on startup by avoiding
classloading and symbol table population, but it also seems to
improve steady state performance of the compiler.

Theory: JIT can optimize more aggressively without the
SynchronizedXxx decorators and the like being in the classloader.
See "Class Heirarchy Analyis" in [1]

This commit does this by:

  - Avoiding use of FromString in pattern matcher, instead
    using an established mechanism to parse system properties.
  - Changes FromString back to use OptManifest. AFAICT, this
    is now only a dependency of scala.tools.cmd.gen.Codegen,
    so this is just a defensive measure.

The REPL still uses runtime reflection, so will pay a little
performance tax.

Benchmark:

    avg shortest 10 times 744ms  # before
    avg shortest 10 times 675ms  # after

[1] https://wikis.oracle.com/display/HotSpotInternals/PerformanceTechniques

1 files changed, 9 insertions, 10 deletions

diff --git a/src/compiler/scala/tools/cmd/FromString.scala b/src/compiler/scala/tools/cmd/FromString.scala
index 433bbb167e..0b074efc0f 100644
--- a/src/compiler/scala/tools/cmd/FromString.scala
+++ b/src/compiler/scala/tools/cmd/FromString.scala
@@ -6,21 +6,20 @@
 package scala.tools
 package cmd
 
-import scala.tools.nsc.io.{ File, Directory }
-import scala.reflect.runtime.{universe => ru}
-import scala.tools.reflect.StdRuntimeTags._
+import nsc.io.{ Path, File, Directory }
+import scala.reflect.OptManifest
 
 /** A general mechanism for defining how a command line argument
  *  (always a String) is transformed into an arbitrary type.  A few
  *  example instances are in the companion object, but in general
  *  either IntFromString will suffice or you'll want custom transformers.
  */
-abstract class FromString[+T](implicit t: ru.TypeTag[T]) extends PartialFunction[String, T] {
+abstract class FromString[+T](implicit m: OptManifest[T]) extends PartialFunction[String, T] {
   def apply(s: String): T
   def isDefinedAt(s: String): Boolean = true
   def zero: T = apply("")
 
-  def targetString: String = t.toString
+  def targetString: String = m.toString
 }
 
 object FromString {
@@ -29,13 +28,13 @@ object FromString {
 
   /** Path related stringifiers.
    */
-  val ExistingDir: FromString[Directory] = new FromString[Directory]()(tagOfDirectory) {
+  val ExistingDir: FromString[Directory] = new FromString[Directory] {
     override def isDefinedAt(s: String) = toDir(s).isDirectory
     def apply(s: String): Directory =
       if (isDefinedAt(s)) toDir(s)
       else cmd.runAndExit(println("'%s' is not an existing directory." format s))
   }
-  def ExistingDirRelativeTo(root: Directory) = new FromString[Directory]()(tagOfDirectory) {
+  def ExistingDirRelativeTo(root: Directory) = new FromString[Directory] {
     private def resolve(s: String) = (toDir(s) toAbsoluteWithRoot root).toDirectory
     override def isDefinedAt(s: String) = resolve(s).isDirectory
     def apply(s: String): Directory =
@@ -46,19 +45,19 @@ object FromString {
   /** Argument expander, i.e. turns single argument "foo bar baz" into argument
    *  list "foo", "bar", "baz".
    */
-  val ArgumentsFromString: FromString[List[String]] = new FromString[List[String]]()(tagOfListOfString) {
+  val ArgumentsFromString: FromString[List[String]] = new FromString[List[String]] {
     def apply(s: String) = toArgs(s)
   }
 
   /** Identity.
    */
-  implicit val StringFromString: FromString[String] = new FromString[String]()(tagOfString) {
+  implicit val StringFromString: FromString[String] = new FromString[String] {
     def apply(s: String): String = s
   }
 
   /** Implicit as the most likely to be useful as-is.
    */
-  implicit val IntFromString: FromString[Int] = new FromString[Int]()(tagOfInt) {
+  implicit val IntFromString: FromString[Int] = new FromString[Int] {
     override def isDefinedAt(s: String)   = safeToInt(s).isDefined
     def apply(s: String)                  = safeToInt(s).get
     def safeToInt(s: String): Option[Int] = try Some(java.lang.Integer.parseInt(s)) catch { case _: NumberFormatException => None }