[vm/compiler] Remove dead code in LocalScope/bitfield in LocalVariable.

There are no callers of CaptureLocalVariables(), and only
CaptureLocalVariables() checks the IsForcedStackBit bitfield of
LocalVariables, so remove that and its setter/getter as well.

TEST=ci (dead code removal)

Issue: #27590

Change-Id: I8032ff8f8cd7a43d3d30f1a4ec4e37cbfcee0a82
Cq-Include-Trybots: luci.dart.try:vm-aot-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/379802
Commit-Queue: Tess Strickland <sstrickl@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

runtime/vm/compiler/frontend/scope_builder.cc

@@ -98,7 +98,6 @@ ScopeBuildingResult* ScopeBuilder::BuildScopes() {
     LocalVariable* suspend_state_var =
         MakeVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                      Symbols::SuspendStateVar(), AbstractType::dynamic_type());
-    suspend_state_var->set_is_forced_stack();
     suspend_state_var->set_invisible(true);
     scope_->AddVariable(suspend_state_var);
     parsed_function_->set_suspend_state_var(suspend_state_var);
@@ -118,7 +117,6 @@ ScopeBuildingResult* ScopeBuilder::BuildScopes() {
   }
 
   LocalVariable* context_var = parsed_function_->current_context_var();
-  context_var->set_is_forced_stack();
   scope_->AddVariable(context_var);
 
   parsed_function_->set_scope(scope_);
@@ -178,7 +176,6 @@ ScopeBuildingResult* ScopeBuilder::BuildScopes() {
         LocalVariable* closure_parameter = MakeVariable(
             TokenPosition::kNoSource, TokenPosition::kNoSource,
             Symbols::ClosureParameter(), AbstractType::dynamic_type());
-        closure_parameter->set_is_forced_stack();
         scope_->InsertParameterAt(pos++, closure_parameter);
       } else if (!function.is_static()) {
         // We use [is_static] instead of [IsStaticFunction] because the latter
@@ -1798,7 +1795,6 @@ void ScopeBuilder::AddExceptionVariable(
 
     // If transformer did not lift the variable then there is no need
     // to lift it into the context when we encounter a YieldStatement.
-    v->set_is_forced_stack();
     current_function_scope_->AddVariable(v);
   }
 
@@ -1820,7 +1816,6 @@ void ScopeBuilder::FinalizeExceptionVariable(
     raw_variable =
         new LocalVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                           symbol, AbstractType::dynamic_type());
-    raw_variable->set_is_forced_stack();
     const bool ok = scope_->AddVariable(raw_variable);
     ASSERT(ok);
   } else {
@@ -1857,7 +1852,6 @@ void ScopeBuilder::AddSwitchVariable() {
     LocalVariable* variable =
         MakeVariable(TokenPosition::kNoSource, TokenPosition::kNoSource,
                      Symbols::SwitchExpr(), AbstractType::dynamic_type());
-    variable->set_is_forced_stack();
     current_function_scope_->AddVariable(variable);
     result_->switch_variable = variable;
   }

runtime/vm/scopes.cc

@@ -555,28 +555,6 @@ LocalScope* LocalScope::RestoreOuterScope(const ContextScope& context_scope) {
   return outer_scope;
 }
 
-void LocalScope::CaptureLocalVariables(LocalScope* top_scope) {
-  ASSERT(top_scope->function_level() == function_level());
-  LocalScope* scope = this;
-  while (scope != top_scope->parent()) {
-    for (intptr_t i = 0; i < scope->num_variables(); i++) {
-      LocalVariable* variable = scope->VariableAt(i);
-      if (variable->is_forced_stack() ||
-          (variable->name().ptr() == Symbols::ExceptionVar().ptr()) ||
-          (variable->name().ptr() == Symbols::SavedTryContextVar().ptr()) ||
-          (variable->name().ptr() == Symbols::ArgDescVar().ptr()) ||
-          (variable->name().ptr() ==
-           Symbols::FunctionTypeArgumentsVar().ptr())) {
-        // Don't capture those variables because the VM expects them to be on
-        // the stack.
-        continue;
-      }
-      scope->CaptureVariable(variable);
-    }
-    scope = scope->parent();
-  }
-}
-
 ContextScopePtr LocalScope::CreateImplicitClosureScope(const Function& func) {
   const intptr_t kNumCapturedVars = 1;
 

runtime/vm/scopes.h

@@ -148,15 +148,6 @@ class LocalVariable : public ZoneAllocated {
     is_awaiter_link_ = value ? IsAwaiterLink::kLink : IsAwaiterLink::kNotLink;
   }
 
-  // Variables marked as forced to stack are skipped and not captured by
-  // CaptureLocalVariables - which iterates scope chain between two scopes
-  // and indiscriminately marks all variables as captured.
-  // TODO(27590) remove the hardcoded list of names from CaptureLocalVariables
-  bool is_forced_stack() const { return IsForcedStackBit::decode(bitfield_); }
-  void set_is_forced_stack() {
-    bitfield_ = IsForcedStackBit::update(true, bitfield_);
-  }
-
   bool is_late() const { return IsLateBit::decode(bitfield_); }
   void set_is_late() { bitfield_ = IsLateBit::update(true, bitfield_); }
 
@@ -235,9 +226,8 @@ class LocalVariable : public ZoneAllocated {
   using IsInvisibleBit = BitField<uint32_t, bool, IsCapturedBit::kNextBit, 1>;
   using IsCapturedParameterBit =
       BitField<uint32_t, bool, IsInvisibleBit::kNextBit, 1>;
-  using IsForcedStackBit =
-      BitField<uint32_t, bool, IsCapturedParameterBit::kNextBit, 1>;
-  using IsLateBit = BitField<uint32_t, bool, IsForcedStackBit ::kNextBit, 1>;
+  using IsLateBit =
+      BitField<uint32_t, bool, IsCapturedParameterBit ::kNextBit, 1>;
 
   enum CovarianceMode {
     kNotCovariant,
@@ -431,10 +421,6 @@ class LocalScope : public ZoneAllocated {
   ContextScopePtr PreserveOuterScope(const Function& function,
                                      intptr_t current_context_level) const;
 
-  // Mark all local variables that are accessible from this scope up to
-  // top_scope (included) as captured unless they are marked as forced to stack.
-  void CaptureLocalVariables(LocalScope* top_scope);
-
   // Creates a LocalScope representing the outer scope of a local function to be
   // compiled. This outer scope contains the variables captured by the function
   // as specified by the given ContextScope, which was created during the