review request (M): 6912064: type profiles need to be more thorough for dynamic language support

[John Rose]

I got a pre-review for 6912064 in January.  These changes still work well; I just used them successfully with a performance tuning experiment.

There was a corner case bug which required an additional 'stopped()' check in graphKit.  Here's the update:
  http://cr.openjdk.java.net/~jrose/6912064/webrev.02/

The four lines in this file starting "// Profile disagrees with this path." are new:
  http://cr.openjdk.java.net/~jrose/6912064/webrev.02/src/share/vm/opto/graphKit.cpp.udiff.html

That is the only difference from January.

Any further comments on this change set?

-- John

FTR, here is the previous communication.  (Yes, it's been a while.)

From: John Rose <John.Rose at Sun.COM>
Date: January 26, 2010 7:14:13 PM PST
To: Vladimir Kozlov <Vladimir.Kozlov at Sun.COM>
Cc: Igor Veresov <Igor.Veresov at Sun.COM>, hotspot-compiler-dev compiler <hotspot-compiler-dev at openjdk.java.net>
Subject: Re: for pre-review (M): 6912064: type profiles need to be more thorough for dynamic language support

On Jan 26, 2010, at 6:59 PM, Vladimir Kozlov wrote:

> Then why you generate the klass check with uncommon trap for instanceof
> for cases when profiling shows that it will fail?

For code like this:

 if (x instanceof String)
   doString((String) x);
 else if (x instanceof Number)
   doNumber((Number) x);

If the 'x' is always an Integer, I want to fold all the tests up from the first instanceof, not the second.

The profile will show when 'x' is of a monomorphic type.  That is more interesting than whether the first check happens to go true or false.

-- John