MIPS32R2: Share address computation

For array accesses the element address has the following structure:
Address = CONST_OFFSET + base_addr + index << ELEM_SHIFT

The address part (index << ELEM_SHIFT) can be shared across array
accesses with the same data type and index.

For example, in the following loop 5 accesses can share address
computation:

void foo(int[] a, int[] b, int[] c) {
  for (i...) {
    a[i] = a[i] + 5;
    b[i] = b[i] + c[i];
  }
}

Test: test-art-host, test-art-target
Change-Id: Id09fa782934aad4ee47669275e7e1a4d7d23b0fa
diff --git a/compiler/optimizing/instruction_simplifier_mips.h b/compiler/optimizing/instruction_simplifier_mips.h
new file mode 100644
index 0000000..22cc2ef
--- /dev/null
+++ b/compiler/optimizing/instruction_simplifier_mips.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_COMPILER_OPTIMIZING_INSTRUCTION_SIMPLIFIER_MIPS_H_
+#define ART_COMPILER_OPTIMIZING_INSTRUCTION_SIMPLIFIER_MIPS_H_
+
+#include "nodes.h"
+#include "optimization.h"
+#include "code_generator_mips.h"
+
+namespace art {
+
+class CodeGenerator;
+
+namespace mips {
+
+class InstructionSimplifierMips : public HOptimization {
+ public:
+  InstructionSimplifierMips(HGraph* graph, CodeGenerator* codegen, OptimizingCompilerStats* stats)
+      : HOptimization(graph, "instruction_simplifier_mips", stats),
+        codegen_(down_cast<CodeGeneratorMIPS*>(codegen)) {}
+
+  static constexpr const char* kInstructionSimplifierMipsPassName = "instruction_simplifier_mips";
+
+  void Run() OVERRIDE;
+
+ private:
+  CodeGeneratorMIPS* codegen_;
+};
+
+}  // namespace mips
+}  // namespace art
+
+#endif  // ART_COMPILER_OPTIMIZING_INSTRUCTION_SIMPLIFIER_MIPS_H_