RFR(L): 8003854: PPC64 (part 115): Introduce lateExpand that expands nodes after register allocation.

[Christian Thalinger]

Before I start to review this I've assigned the bug to you, Goetz:

https://bugs.openjdk.java.net/browse/JDK-8003854

On Oct 2, 2013, at 6:49 AM, "Lindenmaier, Goetz" <goetz.lindenmaier at sap.com> wrote:

> Hi,
> 
> we extended C2 by what we call lateExpand. LateExpand expands nodes
> after register allocation.
> http://cr.openjdk.java.net/~goetz/webrevs/8003854-lateExp/
> 
> Some nodes can not be expanded during matching. E.g., register
> allocation might not be able to deal with the resulting pattern. To
> allow better scheduling in such cases, we introduce lateExpand which
> runs after register allocation. Whether and how nodes are expanded is
> specified in the ad-file. See block.cpp for a detailed
> documentation. We use this for some nodes on ppc, and extensively on
> ia64.
> For an example, see the webrev.
> 
> We added some utility functions in node.hpp and block.hpp used by
> PhaseCFG::LateExpand() or the Node::lateExpand functions.  Also,
> MachConstantBaseNode gets the two new functions, as we need to
> late expand it.
> 
> To skip the walk over the IR if no lateExpand is needed, we use
> Matcher::require_late_expand set in the ad file. This ends up in
> ad_<cpu>.cpp, thus can not be evaluated by the C++ compiler.  If you
> agree, I would use a "const bool EnableLateExpand" in
> globalDefinitions_<cpu>.hpp.  (There is no suitable c2_<xxx>_<cpu>.hpp
> file).
> 
> We allready mailed a webrev with this change after last year's
> JavaOne, but there was no discussion on it.
> Again, this change is 'L', but the code is not used on other
> platforms than PPC64 (so far).  So the impact on those platforms
> should be minimal.
> 
> Please review and test this change.
> 
> Thanks and best regards,
>  Goetz.