ARM: Port instr simplification of array accesses.

After changing the addressing mode for array accesses (in
https://android-review.googlesource.com/248406) the 'add'
instruction that calculates the base address for the array can be
shared across accesses to the same array.

Before https://android-review.googlesource.com/248406:
    add IP, r[Array], r[Index0], LSL #2
    ldr r0, [IP, #12]
    add IP, r[Array], r[Index1], LSL #2
    ldr r0, [IP, #12]

Before this CL:
    add IP. r[Array], #12
    ldr r0, [IP, r[Index0], LSL #2]
    add IP. r[Array], #12
    ldr r0, [IP, r[Index1], LSL #2]

After this CL:
    add IP. r[Array], #12
    ldr r0, [IP, r[Index0], LSL #2]
    ldr r0, [IP, r[Index1], LSL #2]

Link to the original optimization:
    https://android-review.googlesource.com/#/c/127310/

Test: Run ART test suite on Nexus 6.
Change-Id: Iee26f9a0a7ca46abb90e3f60d19d22dc8dee4d8f

1 files changed, 28 insertions, 0 deletions

diff --git a/compiler/optimizing/nodes_shared.h b/compiler/optimizing/nodes_shared.h
index f2d5cf3253..8bd8667f84 100644
--- a/compiler/optimizing/nodes_shared.h
+++ b/compiler/optimizing/nodes_shared.h
@@ -113,6 +113,34 @@ class HBitwiseNegatedRight FINAL : public HBinaryOperation {
   DISALLOW_COPY_AND_ASSIGN(HBitwiseNegatedRight);
 };
 
+
+// This instruction computes an intermediate address pointing in the 'middle' of an object. The
+// result pointer cannot be handled by GC, so extra care is taken to make sure that this value is
+// never used across anything that can trigger GC.
+class HIntermediateAddress FINAL : public HExpression<2> {
+ public:
+  HIntermediateAddress(HInstruction* base_address, HInstruction* offset, uint32_t dex_pc)
+      : HExpression(Primitive::kPrimNot, SideEffects::DependsOnGC(), dex_pc) {
+    SetRawInputAt(0, base_address);
+    SetRawInputAt(1, offset);
+  }
+
+  bool CanBeMoved() const OVERRIDE { return true; }
+  bool InstructionDataEquals(const HInstruction* other ATTRIBUTE_UNUSED) const OVERRIDE {
+    return true;
+  }
+  bool IsActualObject() const OVERRIDE { return false; }
+
+  HInstruction* GetBaseAddress() const { return InputAt(0); }
+  HInstruction* GetOffset() const { return InputAt(1); }
+
+  DECLARE_INSTRUCTION(IntermediateAddress);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(HIntermediateAddress);
+};
+
+
 }  // namespace art
 
 #endif  // ART_COMPILER_OPTIMIZING_NODES_SHARED_H_