ARM64: Instruction simplification for array accesses.

HArrayGet and HArraySet with variable indexes generate two
instructions on arm64, like

    add temp, obj, #data_offset
    ldr out, [temp, index LSL #shift_amount]

When we have multiple accesses to the same array, the initial `add`
instruction is redundant.

This patch introduces the first instruction simplification in the
arm64-specific instruction simplification pass. It splits HArrayGet
and HArraySet using the new arm64-specific IR HIntermediateAddress.
After that we run GVN again to squash the multiple occurrences of
HIntermediateAddress.

Change-Id: I2e3d12fbb07fed07b2cb2f3f47f99f5a032f8312
diff --git a/compiler/optimizing/code_generator_arm64.h b/compiler/optimizing/code_generator_arm64.h
index a068b48..799f1bd 100644
--- a/compiler/optimizing/code_generator_arm64.h
+++ b/compiler/optimizing/code_generator_arm64.h
@@ -382,7 +382,7 @@
                      uint32_t dex_pc,
                      SlowPathCode* slow_path);
 
-  ParallelMoveResolverARM64* GetMoveResolver() { return &move_resolver_; }
+  ParallelMoveResolverARM64* GetMoveResolver() OVERRIDE { return &move_resolver_; }
 
   bool NeedsTwoRegisters(Primitive::Type type ATTRIBUTE_UNUSED) const OVERRIDE {
     return false;