[aarch64-port-dev ] RFR: Disable C2 peephole by default for aarch64

[Felix Yang]

Hi JIT members,

  Currently, the C2 peephole optimization is only enabled by default for
x86 & aarch64 port.
  But we don't have any peephole rules for aarch64 port, scanning the
instruction stream
  in PhasePeephole::do_transform does not make sense but a waste of time
for this port.
  So I am disabling this pass for aarch64 port by default, can anyone
sponsor this if approved?

PATCH:
diff -r a6acc533dfef src/cpu/aarch64/vm/c2_globals_aarch64.hpp
--- a/src/cpu/aarch64/vm/c2_globals_aarch64.hpp Wed Aug 19 16:16:54 2015
+0100
+++ b/src/cpu/aarch64/vm/c2_globals_aarch64.hpp Fri Aug 28 09:28:07 2015
+0800
@@ -69,7 +69,7 @@

 // Peephole and CISC spilling both break the graph, and so makes the
 // scheduler sick.
-define_pd_global(bool, OptoPeephole,                 true);
+define_pd_global(bool, OptoPeephole,                 false);
 define_pd_global(bool, UseCISCSpill,                 true);
 define_pd_global(bool, OptoScheduling,               false);
 define_pd_global(bool, OptoBundling,                 false);