[SubZero] Implement address optimization for MIPS

src/IceOperand.cpp

Index: src/IceOperand.cpp
diff --git a/src/IceOperand.cpp b/src/IceOperand.cpp
index 5d7aa426086648cb51b8cde2ee150eb94d9378d2..3485b602c6d8115b4a7367fb3353a71e56a4dd87 100644
--- a/src/IceOperand.cpp
+++ b/src/IceOperand.cpp
@@ -299,9 +299,10 @@ void VariableTracking::markDef(MetadataKind TrackingKind, const Inst *Instr,
   markUse(TrackingKind, Instr, Node, IsImplicit);
   if (TrackingKind == VMK_Uses)
     return;
-  if (FirstOrSingleDefinition == nullptr)
+  if (FirstOrSingleDefinition == nullptr) {
     FirstOrSingleDefinition = Instr;
-  else if (TrackingKind == VMK_All)
+    FirstOrSingleDefinitionNode = Node;
+  } else if (TrackingKind == VMK_All)
     Definitions.push_back(Instr);
   switch (MultiDef) {
   case MDS_Unknown:
@@ -357,6 +358,19 @@ const Inst *VariableTracking::getSingleDefinition() const {
   return nullptr;
 }
 
+const CfgNode *VariableTracking::getSingleDefinitionNode() const {
+  switch (MultiDef) {
+  case MDS_Unknown:
+  case MDS_MultiDefMultiBlock:
+  case MDS_MultiDefSingleBlock:
+    return nullptr;
+  case MDS_SingleDef:
+    assert(FirstOrSingleDefinitionNode);
+    return FirstOrSingleDefinitionNode;
+  }
+  return nullptr;
+}
+
 const Inst *VariableTracking::getFirstDefinition() const {
   switch (MultiDef) {
   case MDS_Unknown:
@@ -498,6 +512,15 @@ const Inst *VariablesMetadata::getSingleDefinition(const Variable *Var) const {
   return Metadata[VarNum].getSingleDefinition();
 }
 
+const CfgNode *
+VariablesMetadata::getSingleDefinitionNode(const Variable *Var) const {
+  assert(Kind != VMK_Uses);
+  if (!isTracked(Var))
+    return nullptr; // conservative answer
+  SizeT VarNum = Var->getIndex();
+  return Metadata[VarNum].getSingleDefinitionNode();
+}
+
 const Inst *VariablesMetadata::getFirstDefinition(const Variable *Var) const {
   assert(Kind != VMK_Uses);
   if (!isTracked(Var))