[interpreter/runtime] Hole script let/const requiring initialization in NewScriptContext

That way we don't need to generate bytecode for it.

Change-Id: Ie7e17f283cf5a096ab98c4fd01fd346b56b83576
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2004611Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65832}

src/execution/execution.cc

@@ -222,6 +222,13 @@ MaybeHandle<Context> NewScriptContext(Isolate* isolate,
   Handle<Context> result =
       isolate->factory()->NewScriptContext(native_context, scope_info);
 
+  int header = scope_info->ContextHeaderLength();
+  for (int var = 0; var < scope_info->ContextLocalCount(); var++) {
+    if (scope_info->ContextLocalInitFlag(var) == kNeedsInitialization) {
+      result->set(header + var, ReadOnlyRoots(isolate).the_hole_value());
+    }
+  }
+
   Handle<ScriptContextTable> new_script_context_table =
       ScriptContextTable::Extend(script_context, result);
   native_context->set_script_context_table(*new_script_context_table);

src/interpreter/bytecode-generator.cc

@@ -1320,8 +1320,7 @@ void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
 
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED:
-      globals_builder()->record_global_declaration();
-      break;
+      UNREACHABLE();
     case VariableLocation::LOCAL:
       if (variable->binding_needs_init()) {
         Register destination(builder()->Local(variable->index()));
@@ -1376,9 +1375,7 @@ void BytecodeGenerator::VisitFunctionDeclaration(FunctionDeclaration* decl) {
 
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED:
-      AddToEagerLiteralsIfEager(decl->fun());
-      globals_builder()->record_global_declaration();
-      break;
+      UNREACHABLE();
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL: {
       VisitFunctionLiteral(decl->fun());
@@ -1435,9 +1432,26 @@ void BytecodeGenerator::VisitModuleNamespaceImports() {
 
 void BytecodeGenerator::VisitGlobalDeclarations(Declaration::List* decls) {
   RegisterAllocationScope register_scope(this);
-  VisitDeclarations(decls);
+  bool has_global_declaration = false;
+  for (Declaration* decl : *decls) {
+    Variable* var = decl->var();
+    DCHECK(var->is_used());
+    if (var->location() == VariableLocation::UNALLOCATED) {
+      // var or function.
+      has_global_declaration = true;
+      if (decl->IsFunctionDeclaration()) {
+        FunctionDeclaration* f = static_cast<FunctionDeclaration*>(decl);
+        AddToEagerLiteralsIfEager(f->fun());
+      }
+    } else {
+      // let or const. Handled in NewScriptContext.
+      DCHECK(decl->IsVariableDeclaration());
+      DCHECK(IsLexicalVariableMode(var->mode()));
+    }
+  }
 
-  if (!globals_builder()->has_global_declaration()) return;
+  if (!has_global_declaration) return;
+  globals_builder()->record_global_declaration();
   DCHECK(!globals_builder()->processed());
 
   globals_builder()->set_constant_pool_entry(