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

[Lindenmaier, Goetz]

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.