Mark context slots with the parameter they represent so we can easily compute arguments objects

Change-Id: I566ab09800f4a2873aca86423c858b63c58d6d98
Reviewed-on: https://chromium-review.googlesource.com/1105049
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53823}

src/objects/scope-info.cc

@@ -210,9 +210,11 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone, Scope* scope,
         int local_index = var->index() - Context::MIN_CONTEXT_SLOTS;
         DCHECK_LE(0, local_index);
         DCHECK_LT(local_index, context_local_count);
-        uint32_t info = VariableModeField::encode(var->mode()) |
-                        InitFlagField::encode(var->initialization_flag()) |
-                        MaybeAssignedFlagField::encode(var->maybe_assigned());
+        uint32_t info =
+            VariableModeField::encode(var->mode()) |
+            InitFlagField::encode(var->initialization_flag()) |
+            MaybeAssignedFlagField::encode(var->maybe_assigned()) |
+            ParameterNumberField::encode(ParameterNumberField::kMax);
         scope_info->set(context_local_base + local_index, *var->name());
         scope_info->set(context_local_info_base + local_index,
                         Smi::FromInt(info));
@@ -226,7 +228,8 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone, Scope* scope,
         uint32_t properties =
             VariableModeField::encode(var->mode()) |
             InitFlagField::encode(var->initialization_flag()) |
-            MaybeAssignedFlagField::encode(var->maybe_assigned());
+            MaybeAssignedFlagField::encode(var->maybe_assigned()) |
+            ParameterNumberField::encode(ParameterNumberField::kMax);
         scope_info->set(module_var_entry + kModuleVariablePropertiesOffset,
                         Smi::FromInt(properties));
         module_var_entry += kModuleVariableEntryLength;
@@ -237,6 +240,25 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone, Scope* scope,
     }
   }
 
+  if (scope->is_declaration_scope()) {
+    // Mark contexts slots with the parameter number they represent. We walk the
+    // list of parameters. That can include duplicate entries if a parameter
+    // name is repeated. By walking upwards, we'll automatically mark the
+    // context slot with the highest parameter number that uses this variable.
+    // That will be the parameter number that is represented by the context
+    // slot. All lower parameters will only be available on the stack through
+    // the arguments object.
+    for (int i = 0; i < parameter_count; i++) {
+      Variable* parameter = scope->AsDeclarationScope()->parameter(i);
+      if (parameter->location() != VariableLocation::CONTEXT) continue;
+      int index = parameter->index() - Context::MIN_CONTEXT_SLOTS;
+      int info_index = context_local_info_base + index;
+      int info = Smi::ToInt(scope_info->get(info_index));
+      info = ParameterNumberField::update(info, i);
+      scope_info->set(info_index, Smi::FromInt(info));
+    }
+  }
+
   index += 2 * context_local_count;
 
   // If the receiver is allocated, add its index.
@@ -400,9 +422,11 @@ Handle<ScopeInfo> ScopeInfo::CreateForBootstrapping(Isolate* isolate,
   }
   DCHECK_EQ(index, scope_info->ContextLocalInfosIndex());
   if (context_local_count) {
-    const uint32_t value = VariableModeField::encode(VariableMode::kConst) |
-                           InitFlagField::encode(kCreatedInitialized) |
-                           MaybeAssignedFlagField::encode(kNotAssigned);
+    const uint32_t value =
+        VariableModeField::encode(VariableMode::kConst) |
+        InitFlagField::encode(kCreatedInitialized) |
+        MaybeAssignedFlagField::encode(kNotAssigned) |
+        ParameterNumberField::encode(ParameterNumberField::kMax);
     scope_info->set(index++, Smi::FromInt(value));
   }
 
@@ -581,12 +605,12 @@ String* ScopeInfo::FunctionDebugName() const {
 
 int ScopeInfo::StartPosition() const {
   DCHECK(HasPositionInfo());
-  return Smi::cast(get(PositionInfoIndex()))->value();
+  return Smi::ToInt(get(PositionInfoIndex()));
 }
 
 int ScopeInfo::EndPosition() const {
   DCHECK(HasPositionInfo());
-  return Smi::cast(get(PositionInfoIndex() + 1))->value();
+  return Smi::ToInt(get(PositionInfoIndex() + 1));
 }
 
 void ScopeInfo::SetPositionInfo(int start, int end) {
@@ -636,6 +660,22 @@ InitializationFlag ScopeInfo::ContextLocalInitFlag(int var) const {
   return InitFlagField::decode(value);
 }
 
+bool ScopeInfo::ContextLocalIsParameter(int var) const {
+  DCHECK_LE(0, var);
+  DCHECK_LT(var, ContextLocalCount());
+  DCHECK_LT(var, ParameterCount());
+  int info_index = ContextLocalInfosIndex() + var;
+  int value = Smi::ToInt(get(info_index));
+  return ParameterNumberField::decode(value) != ParameterNumberField::kMax;
+}
+
+uint32_t ScopeInfo::ContextLocalParameterNumber(int var) const {
+  DCHECK(ContextLocalIsParameter(var));
+  int info_index = ContextLocalInfosIndex() + var;
+  int value = Smi::ToInt(get(info_index));
+  return ParameterNumberField::decode(value);
+}
+
 MaybeAssignedFlag ScopeInfo::ContextLocalMaybeAssignedFlag(int var) const {
   DCHECK_LE(0, var);
   DCHECK_LT(var, ContextLocalCount());
@@ -955,9 +995,8 @@ String* ModuleInfo::RegularExportLocalName(int i) const {
 }
 
 int ModuleInfo::RegularExportCellIndex(int i) const {
-  return Smi::cast(regular_exports()->get(i * kRegularExportLength +
-                                          kRegularExportCellIndexOffset))
-      ->value();
+  return Smi::ToInt(regular_exports()->get(i * kRegularExportLength +
+                                           kRegularExportCellIndexOffset));
 }
 
 FixedArray* ModuleInfo::RegularExportExportNames(int i) const {

src/objects/scope-info.h

@@ -120,6 +120,9 @@ class ScopeInfo : public FixedArray {
   // Return the initialization flag of the given context local.
   InitializationFlag ContextLocalInitFlag(int var) const;
 
+  bool ContextLocalIsParameter(int var) const;
+  uint32_t ContextLocalParameterNumber(int var) const;
+
   // Return the initialization flag of the given context local.
   MaybeAssignedFlag ContextLocalMaybeAssignedFlag(int var) const;
 
@@ -321,6 +324,8 @@ class ScopeInfo : public FixedArray {
   class VariableModeField : public BitField<VariableMode, 0, 3> {};
   class InitFlagField : public BitField<InitializationFlag, 3, 1> {};
   class MaybeAssignedFlagField : public BitField<MaybeAssignedFlag, 4, 1> {};
+  class ParameterNumberField
+      : public BitField<uint32_t, MaybeAssignedFlagField::kNext, 16> {};
 
   friend class ScopeIterator;
   friend std::ostream& operator<<(std::ostream& os,

src/runtime/runtime-scopes.cc

@@ -428,43 +428,24 @@ Handle<JSObject> NewSloppyArguments(Isolate* isolate, Handle<JSFunction> callee,
         --index;
       }
 
-      Handle<ScopeInfo> scope_info(callee->shared()->scope_info());
-      while (index >= 0) {
-        // Detect duplicate names to the right in the parameter list.
-        Handle<String> name(scope_info->ParameterName(index));
-        int context_local_count = scope_info->ContextLocalCount();
-        bool duplicate = false;
-        for (int j = index + 1; j < parameter_count; ++j) {
-          if (scope_info->ParameterName(j) == *name) {
-            duplicate = true;
-            break;
-          }
-        }
-
-        if (duplicate) {
-          // This goes directly in the arguments array with a hole in the
-          // parameter map.
-          arguments->set(index, parameters[index]);
-          parameter_map->set_the_hole(index + 2);
-        } else {
-          // The context index goes in the parameter map with a hole in the
-          // arguments array.
-          int context_index = -1;
-          for (int j = 0; j < context_local_count; ++j) {
-            if (scope_info->ContextLocalName(j) == *name) {
-              context_index = j;
-              break;
-            }
-          }
-
-          DCHECK_GE(context_index, 0);
-          arguments->set_the_hole(index);
-          parameter_map->set(
-              index + 2,
-              Smi::FromInt(Context::MIN_CONTEXT_SLOTS + context_index));
-        }
+      Handle<ScopeInfo> scope_info(callee->shared()->scope_info(), isolate);
 
-        --index;
+      // First mark all mappable slots as unmapped and copy the values into the
+      // arguments object.
+      for (int i = 0; i < mapped_count; i++) {
+        arguments->set(i, parameters[i]);
+        parameter_map->set_the_hole(i + 2);
+      }
+
+      // Walk all context slots to find context allocated parameters. Mark each
+      // found parameter as mapped.
+      for (int i = 0; i < scope_info->ContextLocalCount(); i++) {
+        if (!scope_info->ContextLocalIsParameter(i)) continue;
+        int parameter = scope_info->ContextLocalParameterNumber(i);
+        if (parameter >= mapped_count) continue;
+        arguments->set_the_hole(parameter);
+        Smi* slot = Smi::FromInt(Context::MIN_CONTEXT_SLOTS + i);
+        parameter_map->set(parameter + 2, slot);
       }
     } else {
       // If there is no aliasing, the arguments object elements are not