Compute the def-use list on-demand by walking the dominator tree.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 250db29bc0f90df213cd3d233fe1f33abe37effb..51ec2e1270ef79cbfaebfdbfa48435a8b2304f6c 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -73,20 +73,6 @@ bool CheckClassComp::AttributesEqual(Computation* other) const {
 }
 
 
-UseVal::UseVal(Definition* definition)
-    : definition_(definition), next_use_(NULL), previous_use_(NULL) {
-  AddToUseList();
-}
-
-
-void UseVal::SetDefinition(Definition* definition) {
-  ASSERT(definition != NULL);
-  RemoveFromUseList();
-  definition_ = definition;
-  AddToUseList();
-}
-
-
 // Returns true if the value represents a constant.
 bool UseVal::BindsToConstant() const {
   BindInstr* bind = definition()->AsBind();
@@ -121,34 +107,6 @@ const Object& UseVal::BoundConstant() const {
 }
 
 
-void UseVal::RemoveFromUseList() {
-  ASSERT(definition_ != NULL);
-  if (next_use_ != NULL) {
-    next_use_->previous_use_ = previous_use_;
-  }
-  if (previous_use_ != NULL) {
-    previous_use_->next_use_ = next_use_;
-  } else {
-    // This is the head of the list.
-    ASSERT(definition_->use_list() == this);
-    definition_->set_use_list(next_use_);
-  }
-  previous_use_ = next_use_ = NULL;
-  definition_ = NULL;
-}
-
-
-void UseVal::AddToUseList() {
-  ASSERT(next_use_ == NULL && previous_use_ == NULL && definition_ != NULL);
-  UseVal* head = definition_->use_list();
-  if (head != NULL) {
-    next_use_ = head;
-    head->previous_use_ = this;
-  }
-  definition_->set_use_list(this);
-}
-
-
 MethodRecognizer::Kind MethodRecognizer::RecognizeKind(
     const Function& function) {
   // Only core and math library methods can be recognized.
@@ -226,7 +184,6 @@ Instruction* Instruction::RemoveFromGraph(bool return_previous) {
   // that the instruction is removed from the graph.
   set_previous(NULL);
   set_next(NULL);
-  ASSERT(!IsDefinition() || AsDefinition()->use_list() == NULL);
   return return_previous ? prev_instr : next_instr;
 }
 
@@ -406,22 +363,20 @@ void Instruction::RecordAssignedVars(BitVector* assigned_vars,
 
 
 void Definition::ReplaceUsesWith(Definition* other) {
-  UseVal* head = use_list();
-  if (head == NULL) return;
-
-  UseVal* current = head;
-  while (current->next_use() != NULL) {
-    current->definition_ = other;
-    current = current->next_use();
+  while (instr_use_list_ != NULL) {
+    UseVal* current = instr_use_list_;
+    instr_use_list_ = instr_use_list_->next_use();
+    current->set_definition(other);
+    current->set_next_use(other->instr_use_list());
+    other->set_instr_use_list(current);
   }
-  current->definition_ = other;
-
-  if (other->use_list() != NULL) {
-    current->next_use_ = other->use_list();
-    other->use_list()->previous_use_ = current;
+  while (env_use_list_ != NULL) {
+    UseVal* current = env_use_list_;
+    env_use_list_ = env_use_list_->next_use();
+    current->set_definition(other);
+    current->set_next_use(other->env_use_list());
+    other->set_env_use_list(current);
   }
-  other->set_use_list(head);
-  set_use_list(NULL);
 }
 
 
@@ -1085,7 +1040,6 @@ Definition* StrictCompareComp::TryReplace(BindInstr* instr) const {
     // Remove the constant from the graph.
     BindInstr* right = right_use->definition()->AsBind();
     if (right != NULL) {
-      right->set_use_list(NULL);
       right->RemoveFromGraph();
     }
     // Return left subexpression as the replacement for this instruction.