RFR(XS): 8030976: untaken paths should be more vigorously pruned at highest optimization level

[Christian Thalinger]

On May 22, 2014, at 4:53 AM, Rickard Bäckman <rickard.backman at oracle.com> wrote:

> Hi all,
> 
> can I please have reviews for this change.
> The patch makes C2 place uncommon traps on previously untaken branches
> much more aggressively (we are simply trusting the profiling more). 
> This improves performance for a couple of different patterns.
> 
> Example:
> 
> class Test {
>  public int[] array = new int[] = { 1, 1, 2, 3, 5, 8, 13 };
> 
>  public void some_method() {
>    for (int i = 0; i < array.length; i++) {
>      if (array[i] < 255) {
>        some_call();
>      } else {
>        some_other_call();
>      }
>    }
>  }
> }
> 
> Where we previously if the else branch had never been taken rarely would
> inline the some_other_call and when array escapes we can't make
> assumptions on non-changing lengths, call killing registers, etc.
> 
> On some of the Nashorn benchmark this patch increases score by 35%,
> others don't see any change at all. No difference on SpecJBB 2005.
> More performance numbers / microbenchmark in the comments of the bug.

One comment says:

"Trying to get numbers from some bigger benchmarks as well.”

Did you only run SPECjbb2005 or others as well?

> 
> Webrev: http://cr.openjdk.java.net/~rbackman/8030976/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8030976
> 
> Thanks
> /R