64 bit jvm generates slow array copying code

Name: ks84122 Date: 06/10/2002


The example below demonstrates that the 64 bit server compiler generates
poor array copying code. Reproducible on Solaris 9, Solaris 7 in 64 bit
mode, JDK 1.4.1 (solaris-sparcv9)

Original description from HP:
=============================

public class copybench
{
  static char[] source = new char[2000];
  static char[] target = new char[5000];

  public static long run(int loopcount, boolean usesystem, int source_off,
    int target_off, int len)
  {
    int indx, indx2;
    long starttime = System.currentTimeMillis();
   
    char[] s = source;
    char[] t = target;
    for (indx2=loopcount; --indx2 >= 0; )
    {
      if (! usesystem)
      {
        for (indx = 0; indx < len; ++indx)
        {
          t[target_off + indx] = s[source_off + indx];
        }
      }
      else
      {
        System.arraycopy(s, source_off, t, target_off, len);
      }
    }
    long endtime = System.currentTimeMillis();
    return endtime - starttime;
  }

  public static void main(String argv[])
  {
    int indx;
    for (indx=0; indx < source.length; ++indx)
    {
      source[indx] = (char) indx;
    }
    System.out.println((argv.length == 0) + " warmup " + (long) argv.length);
    run(2,true,0,0,2000);
    run(2,false,0,0,2000);
    for (indx=100000; indx > 0; --indx)
    {
      run(1,true,1,1,16); // warm up run
      run(1,false,1,1,16); // warm up run
    }
    System.out.println("start");
    for (indx=10; indx > 0; --indx)
    {
      System.out.println("system copy " + run(99990,true,240,200,20));
      System.out.println("java copy " + run(99990,false,240,200,20));
    }
  }

}

7%/export/home1/jgragg/jdk1.4.0_01/bin/java -server copybench
...
system copy 38
java copy 28
8%/export/home1/jgragg/jdk1.4.0_01/bin/java -d64 -server copybench
...
system copy 31
java copy 52 (52 ms vs 28 ms is almost 2x slower)

When I look at the assembly code generated, the 32 bit jvm generates
a clean unrolled copying loop. The 64 bit jvm generates something
that is quite ugly and slower code.
(Review ID: 153345)
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