为什么Scala中的这个函数调用没有被优化掉？(Why this function call in Scala is not optimized away?)

 我正在使用Scala 2.10.3运行此程序： 
 
object Test {
  def main(args: Array[String]) { 
    def factorial(x: BigInt): BigInt = 
      if (x == 0) 1 else x * factorial(x - 1)

    val N = 1000
    val t = new Array[Long](N)
    var r: BigInt = 0

    for (i <- 0 until N) {
      val t0 = System.nanoTime()

      r = r + factorial(300)
      t(i) = System.nanoTime()-t0
    }

    val ts = t.sortWith((x, y) => x < y)

    for (i <- 0 to 10)
      print(ts(i) + "  ")

    println("***  " + ts(N/2) + "\n" + r)
  }  
}
 
 并且在每次循环迭代期间评估具有常量参数的纯函数factorial （基于时序结果的结论）。 第一次调用后，优化器不应该重用函数调用结果吗？ 
 
 我正在使用Scala IDE for Eclipse。 编译器是否有任何优化标志，这可能会产生更高效的代码？ 

I'm running this program with Scala 2.10.3:
 
object Test {
  def main(args: Array[String]) { 
    def factorial(x: BigInt): BigInt = 
      if (x == 0) 1 else x * factorial(x - 1)

    val N = 1000
    val t = new Array[Long](N)
    var r: BigInt = 0

    for (i <- 0 until N) {
      val t0 = System.nanoTime()

      r = r + factorial(300)
      t(i) = System.nanoTime()-t0
    }

    val ts = t.sortWith((x, y) => x < y)

    for (i <- 0 to 10)
      print(ts(i) + "  ")

    println("***  " + ts(N/2) + "\n" + r)
  }  
}
 
and call to a pure function factorial with constant argument is evaluated during each loop iteration (conclusion based on timing results). Shouldn't the optimizer reuse function call result after the first call? 
 
I'm using Scala IDE for Eclipse. Are there any optimization flags for the compiler, which may produce more efficient code?

原文：https://stackoverflow.com/questions/19316276