Review Request: Backport some Hotspot defaults for AMD Bulldozer processor

[Deneau, Tom]

Please review this patch which backports some Hotspot defaults for AMD's new Bulldozer which had already been accepted into Hotspot 21 in JDK7 General Release.  These defaults allow the Bulldozer processor family to get the best performance.

The webrev is at

  http://cr.openjdk.java.net/~tdeneau/openjdk6-bd-defaults/webrev.01/<http://cr.openjdk.java.net/~tdeneau/3dnow-cpuid/webrev.01/>


The changes consist of:

*         default for AllocatePrefetchStyle goes to 0, that is, no SW Prefetch

*         UseXMMForArrayCopy, UseUnalignedLoadStores and UseSSE42Intrinsics default to true

*         changes the logic for detecting whether or not a processor supports the 3dnow prefetchw and prefetch instructions.   A separate CPUID bit (defined in about 2007) allows a processor to support 3dnow prefetch instructions without supporting the whole 3dnow instruction set.  The Bulldozer processors from AMD are the first that support 3dnow prefetch without supporting the 3dnow instruction set.  The logic change is really one small change in src/cpu/x86/vm/vm_version_x86.hpp but to clarify things I changed a function name from supports_3dnow() to supports_3dnow_prefetch() which is really what was meant all along.  This was the reason the other files changed.  I did not make any change in src/cpu/x86/vm/x86_64.ad since that was not checking for 3dnow support.


-- Tom Deneau, AMD


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