Add functions for setting an environment and rebinding a use.

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 43c04212b9f5851d88d8bfa2e2acaf8113c87df3..616c21418869b43a25bf8f33f994d79c64f1f910 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -318,6 +318,25 @@ FOR_EACH_INSTRUCTION(DEFINE_ACCEPT)
 #undef DEFINE_ACCEPT
 
 
+void Instruction::SetEnvironment(Environment* deopt_env) {
+  intptr_t use_index = 0;
+  for (Environment::DeepIterator it(deopt_env); !it.Done(); it.Advance()) {
+    Value* use = it.CurrentValue();
+    use->set_instruction(this);
+    use->set_use_index(use_index++);
+  }
+  env_ = deopt_env;
+}
+
+
+void Instruction::RemoveEnvironment() {
+  for (Environment::DeepIterator it(env()); !it.Done(); it.Advance()) {
+    it.CurrentValue()->RemoveFromUseList();
+  }
+  env_ = NULL;
+}
+
+
 Instruction* Instruction::RemoveFromGraph(bool return_previous) {
   ASSERT(!IsBlockEntry());
   ASSERT(!IsControl());
@@ -326,29 +345,23 @@ Instruction* Instruction::RemoveFromGraph(bool return_previous) {
   ASSERT(!IsReThrow());
   ASSERT(!IsGoto());
   ASSERT(previous() != NULL);
+  // We cannot assert that the instruction, if it is a definition, has no
+  // uses.  This function is used to remove instructions from the graph and
+  // reinsert them elsewhere (e.g., hoisting).
   Instruction* prev_instr = previous();
   Instruction* next_instr = next();
   ASSERT(next_instr != NULL);
   ASSERT(!next_instr->IsBlockEntry());
   prev_instr->LinkTo(next_instr);
-  // Reset successor and previous instruction to indicate
-  // that the instruction is removed from the graph.
+  UnuseAllInputs();
+  // Reset the successor and previous instruction to indicate that the
+  // instruction is removed from the graph.
   set_previous(NULL);
   set_next(NULL);
   return return_previous ? prev_instr : next_instr;
 }
 
 
-void Instruction::InsertBefore(Instruction* next) {
-  ASSERT(previous_ == NULL);
-  ASSERT(next_ == NULL);
-  next_ = next;
-  previous_ = next->previous_;
-  next->previous_ = this;
-  previous_->next_ = this;
-}
-
-
 void Instruction::InsertAfter(Instruction* prev) {
   ASSERT(previous_ == NULL);
   ASSERT(next_ == NULL);
@@ -356,6 +369,13 @@ void Instruction::InsertAfter(Instruction* prev) {
   next_ = prev->next_;
   next_->previous_ = this;
   previous_->next_ = this;
+
+  // Update def-use chains whenever instructions are added to the graph
+  // after initial graph construction.
+  for (intptr_t i = InputCount() - 1; i >= 0; --i) {
+    Value* input = InputAt(i);
+    input->definition()->AddInputUse(input);
+  }
 }
 
 
@@ -472,7 +492,6 @@ void Value::RemoveFromUseList() {
     if (next != NULL) next->set_previous_use(prev);
   }
 
-  set_definition(NULL);
   set_previous_use(NULL);
   set_next_use(NULL);
 }
@@ -537,23 +556,15 @@ void Definition::ReplaceWith(Definition* other,
   }
   // Take other's environment from this definition.
   ASSERT(other->env() == NULL);
-  intptr_t use_index = 0;
-  for (Environment::DeepIterator it(env()); !it.Done(); it.Advance()) {
-    Value* use = it.CurrentValue();
-    use->set_instruction(other);
-    use->set_use_index(use_index++);
-  }
-  other->set_env(env());
-  set_env(NULL);
+  other->SetEnvironment(env());
+  env_ = NULL;
   // Replace all uses of this definition with other.
   ReplaceUsesWith(other);
   // Reuse this instruction's SSA name for other.
   ASSERT(!other->HasSSATemp());
   if (HasSSATemp()) other->set_ssa_temp_index(ssa_temp_index());
-  // Remove this definition's input uses.
-  UnuseAllInputs();
 
-  // Finally remove this definition from the graph.
+  // Finally insert the other definition in place of this one in the graph.
   previous()->LinkTo(other);
   if ((iterator != NULL) && (this == iterator->Current())) {
     // Remove through the iterator.
@@ -561,6 +572,8 @@ void Definition::ReplaceWith(Definition* other,
     iterator->RemoveCurrentFromGraph();
   } else {
     other->LinkTo(next());
+    // Remove this definition's input uses.
+    UnuseAllInputs();
   }
   set_previous(NULL);
   set_next(NULL);
@@ -583,23 +596,18 @@ void BranchInstr::RawSetInputAt(intptr_t i, Value* value) {
 // A misleadingly named function for use in template functions that replace
 // both definitions with definitions and branch comparisons with
 // comparisons.  In the branch case, leave the branch intact and replace its
-// comparison with another comparison.
+// comparison with a new comparison not currently in the graph.
 void BranchInstr::ReplaceWith(ComparisonInstr* other,
                               ForwardInstructionIterator* ignored) {
-  // Record the new comparison's input uses.
-  for (intptr_t i = other->InputCount() - 1; i >= 0; --i) {
-    Value* input = other->InputAt(i);
-    input->definition()->AddInputUse(input);
-  }
   SetComparison(other);
 }
 
 
 void BranchInstr::SetComparison(ComparisonInstr* comp) {
-  // The new comparison's input uses are already recorded in their
-  // definition's use lists.
   for (intptr_t i = comp->InputCount() - 1; i >= 0; --i) {
-    comp->InputAt(i)->set_instruction(this);
+    Value* input = comp->InputAt(i);
+    input->definition()->AddInputUse(input);
+    input->set_instruction(this);
   }
   // There should be no need to copy or unuse an environment.
   ASSERT(comparison()->env() == NULL);
@@ -1174,9 +1182,7 @@ Definition* AssertAssignableInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
     // It is ok to insert instructions before the current during
     // forward iteration.
     optimizer->InsertBefore(this, null_constant, NULL, Definition::kValue);
-    instantiator_type_arguments()->RemoveFromUseList();
-    instantiator_type_arguments()->set_definition(null_constant);
-    null_constant->AddInputUse(instantiator_type_arguments());
+    instantiator_type_arguments()->BindTo(null_constant);
   }
   return this;
 }
@@ -1205,9 +1211,6 @@ Instruction* BranchInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
         (comp->input_use_list()->next_use() == NULL) &&
         (comp->env_use_list() == NULL)) {
       comp->RemoveFromGraph();
-      // It is safe to pass a NULL iterator because we're replacing the
-      // comparison wrapped in a BranchInstr which does not modify the
-      // linked list of instructions.
       SetComparison(comp);
       if (FLAG_trace_optimization) {
         OS::Print("Merging comparison v%"Pd"\n", comp->ssa_temp_index());
@@ -1541,14 +1544,11 @@ void Environment::DeepCopyTo(Instruction* instr) const {
   }
 
   Environment* copy = DeepCopy();
-  intptr_t use_index = 0;
+  instr->SetEnvironment(copy);
   for (Environment::DeepIterator it(copy); !it.Done(); it.Advance()) {
     Value* value = it.CurrentValue();
-    value->set_instruction(instr);
-    value->set_use_index(use_index++);
     value->definition()->AddEnvUse(value);
   }
-  instr->set_env(copy);
 }
 
 
@@ -1560,6 +1560,7 @@ void Environment::DeepCopyToOuter(Instruction* instr) const {
   ASSERT(instr->env()->outer() == NULL);
   intptr_t argument_count = instr->env()->fixed_parameter_count();
   Environment* copy = DeepCopy(values_.length() - argument_count);
+  instr->env()->outer_ = copy;
   intptr_t use_index = instr->env()->Length();  // Start index after inner.
   for (Environment::DeepIterator it(copy); !it.Done(); it.Advance()) {
     Value* value = it.CurrentValue();
@@ -1567,7 +1568,6 @@ void Environment::DeepCopyToOuter(Instruction* instr) const {
     value->set_use_index(use_index++);
     value->definition()->AddEnvUse(value);
   }
-  instr->env()->outer_ = copy;
 }