[SubZero] Implement address optimization for MIPS

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index a2e9f9e77c51ad1be81599b0ad88ba32579bb37c..0c606456231db9282fa436e4f2ec4534053379dd 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -980,6 +980,7 @@ public:
   MultiBlockState getMultiBlock() const { return MultiBlock; }
   const Inst *getFirstDefinitionSingleBlock() const;
   const Inst *getSingleDefinition() const;
+  const CfgNode *getSingleDefinitionNode() const;
   const Inst *getFirstDefinition() const;
   const InstDefList &getLatterDefinitions() const { return Definitions; }
   CfgNode *getNode() const { return SingleUseNode; }
@@ -997,6 +998,7 @@ private:
   /// the earliest definition), in increasing order of instruction number.
   InstDefList Definitions; /// Only used if Kind==VMK_All
   const Inst *FirstOrSingleDefinition = nullptr;
+  const CfgNode *FirstOrSingleDefinitionNode = nullptr;
   RegWeight UseWeight;
 };
 
@@ -1034,6 +1036,7 @@ public:
   /// Returns the definition instruction of the given Variable, when the
   /// variable has exactly one definition. Otherwise, nullptr is returned.
   const Inst *getSingleDefinition(const Variable *Var) const;
+  const CfgNode *getSingleDefinitionNode(const Variable *Var) const;
   /// getFirstDefinition() and getLatterDefinitions() are used together to
   /// return the complete set of instructions that define the given Variable,
   /// regardless of whether the definitions are within the same block (in