Range.foreach optimization.

This makes code like

  0 to 100 foreach (x += _)

as fast as (often faster than, in fact) a while loop.  See the
comment in Range for the gory details.  More investigation should
be done regarding total impact on inlining behavior.
Review by @odersky.

1 files changed, 61 insertions, 0 deletions

diff --git a/test/benchmarks/src/scala/collection/immutable/range-bench.scala b/test/benchmarks/src/scala/collection/immutable/range-bench.scala
new file mode 100644
index 0000000000..e167ff04e8
--- /dev/null
+++ b/test/benchmarks/src/scala/collection/immutable/range-bench.scala
@@ -0,0 +1,61 @@
+package scala.collection.immutable
+package benchmarks
+
+object RangeTest {
+  // not inlined any more, needs investigation
+  // 
+  // class XXS {
+  //   private val array = Array.range(0, 100)
+  //   def tst = { var sum = 0; for (i <- 0 until array.length) sum += array(i); sum }
+  // }
+  
+  var x: Int = 0
+  
+  def foreachSum(max: Int): Int = {
+    var sum = 0
+    1 to max foreach (sum += _)
+    sum
+  }
+  def whileSum(max: Int) = {
+    var sum = 0
+    var num = 1
+    while (num <= max) {
+      sum += num
+      num += 1
+    }
+    sum
+  }
+
+  def show(max: Int, foreachNanos: Long, whileNanos: Long) {
+    val winner = if (foreachNanos < whileNanos) "foreachSum" else "whileSum"
+    val ratio = if (foreachNanos < whileNanos) foreachNanos.toDouble / whileNanos else whileNanos.toDouble / foreachNanos
+    println("1 to %d:, %12s wins, %.3f:  foreach %.3f   while %.3f".format(
+      max, winner, ratio, 
+      foreachNanos.toDouble / 1000000L, 
+      whileNanos.toDouble / 1000000L)
+    )
+  }
+  
+  def run(max: Int) = {
+    val foreachFirst = util.Random.nextBoolean
+    val t1 = System.nanoTime
+    x = if (foreachFirst) foreachSum(max) else whileSum(max)
+    val t2 = System.nanoTime
+    x = if (foreachFirst) whileSum(max) else foreachSum(max)
+    val t3 = System.nanoTime
+    
+    val foreachNanos = if (foreachFirst) t2 - t1 else t3 - t2
+    val whileNanos = if (foreachFirst) t3 - t2 else t2 - t1
+    show(max, foreachNanos, whileNanos)
+  }
+
+  def main(args: Array[String]): Unit = {
+    var max = if (args.isEmpty) 100 else args(0).toInt
+    while (max > 0) {    
+      run(max)
+      run(max)
+      run(max)
+      max += (max / 7)
+    }
+  }
+}