[vm,bytecode] Allocate objects lazily in bytecode generator

Previously, bytecode generator was allocating a bunch of objects
eagerly when starting bytecode generation for a member. Most of these
objects are maps and lists which are needed only under certain
circumstances. With this change these objects are allocated more lazily,
only when needed.

Also, this CL fixes crash in LinkReader.setOffset when reading/dumping
bytecode.

Change-Id: I11c561e4f00c456e92f42530d3d4e6008b5f5daf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/122407
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov

pkg/vm/lib/bytecode/bytecode_serialization.dart

@@ -457,7 +457,7 @@ class LinkWriter {
 class LinkReader {
   final _map = <Type, Map<int, BytecodeDeclaration>>{};
 
-  void setOffset<T>(BytecodeDeclaration target, int offset) {
+  void setOffset<T extends BytecodeDeclaration>(T target, int offset) {
     final offsetToObject = (_map[T] ??= <int, BytecodeDeclaration>{});
     final previous = offsetToObject[offset];
     if (previous != null) {

pkg/vm/lib/bytecode/gen_bytecode.dart

@@ -1656,18 +1656,18 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
       return;
     }
 
-    labeledStatements = <LabeledStatement, Label>{};
-    switchCases = <SwitchCase, Label>{};
-    tryCatches = <TryCatch, TryBlock>{};
-    finallyBlocks = <TryFinally, List<FinallyBlock>>{};
+    labeledStatements = null;
+    switchCases = null;
+    tryCatches = null;
+    finallyBlocks = null;
     yieldPoints = null; // Initialized when entering sync-yielding closure.
-    contextLevels = <TreeNode, int>{};
-    closures = <ClosureDeclaration>[];
+    contextLevels = null;
+    closures = null;
     initializedFields = null; // Tracked for constructors only.
     nullableFields = const <ObjectHandle>[];
     cp = new ConstantPool(stringTable, objectTable);
     asm = new BytecodeAssembler(options);
-    savedAssemblers = <BytecodeAssembler>[];
+    savedAssemblers = null;
     currentLoopDepth = 0;
     savedMaxSourcePositions = <int>[];
     maxSourcePosition = node.fileOffset;
@@ -1780,7 +1780,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
             finalizeSourcePositions(),
             finalizeLocalVariables(),
             nullableFields,
-            closures,
+            closures ?? const <ClosureDeclaration>[],
             parameterFlags,
             forwardingStubTargetCpIndex,
             defaultFunctionTypeArgsCpIndex);
@@ -2344,6 +2344,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
   }
 
   void _pushAssemblerState() {
+    savedAssemblers ??= <BytecodeAssembler>[];
     savedAssemblers.add(asm);
     asm = new BytecodeAssembler(options);
   }
@@ -2377,6 +2378,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
     List<Label> savedYieldPoints = yieldPoints;
     yieldPoints = locals.isSyncYieldingFrame ? <Label>[] : null;
 
+    closures ??= <ClosureDeclaration>[];
     final int closureIndex = closures.length;
     final closure = getClosureDeclaration(node, function, name, closureIndex,
         savedIsClosure ? parentFunction : enclosingMember);
@@ -4014,7 +4016,9 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
   @override
   visitLabeledStatement(LabeledStatement node) {
     final label = new Label();
+    labeledStatements ??= new Map<LabeledStatement, Label>();
     labeledStatements[node] = label;
+    contextLevels ??= new Map<TreeNode, int>();
     contextLevels[node] = locals.currentContextLevel;
     _generateNode(node.body);
     asm.bind(label);
@@ -4057,6 +4061,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
 
   @override
   visitSwitchStatement(SwitchStatement node) {
+    contextLevels ??= new Map<TreeNode, int>();
     contextLevels[node] = locals.currentContextLevel;
 
     _generateNode(node.expression);
@@ -4075,6 +4080,8 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
         node.cases.length, (_) => new Label(allowsBackwardJumps: true));
     final equalsArgDesc = objectTable.getArgDescHandle(2);
 
+    switchCases ??= new Map<SwitchCase, Label>();
+
     Label defaultLabel = done;
     for (int i = 0; i < node.cases.length; i++) {
       final SwitchCase switchCase = node.cases[i];
@@ -4244,6 +4251,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
 
     final TryBlock tryBlock = _startTryBlock(node);
     tryBlock.isSynthetic = node.isSynthetic;
+    tryCatches ??= new Map<TryCatch, TryBlock>();
     tryCatches[node] = tryBlock; // Used by rethrow.
 
     _generateNode(node.body);
@@ -4315,6 +4323,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
 
     final TryBlock tryBlock = _startTryBlock(node);
     tryBlock.isSynthetic = true;
+    finallyBlocks ??= new Map<TryFinally, List<FinallyBlock>>();
     finallyBlocks[node] = <FinallyBlock>[];
 
     _generateNode(node.body);

pkg/vm/lib/bytecode/local_vars.dart

@@ -17,18 +17,13 @@ import 'options.dart' show BytecodeOptions;
 import '../metadata/direct_call.dart' show DirectCallMetadata;
 
 class LocalVariables {
-  final Map<TreeNode, Scope> _scopes = <TreeNode, Scope>{};
-  final Map<VariableDeclaration, VarDesc> _vars =
-      <VariableDeclaration, VarDesc>{};
-  final Map<TreeNode, List<int>> _temps = <TreeNode, List<int>>{};
-  final Map<TreeNode, VariableDeclaration> _capturedSavedContextVars =
-      <TreeNode, VariableDeclaration>{};
-  final Map<TreeNode, VariableDeclaration> _capturedExceptionVars =
-      <TreeNode, VariableDeclaration>{};
-  final Map<TreeNode, VariableDeclaration> _capturedStackTraceVars =
-      <TreeNode, VariableDeclaration>{};
-  final Map<ForInStatement, VariableDeclaration> _capturedIteratorVars =
-      <ForInStatement, VariableDeclaration>{};
+  final _scopes = new Map<TreeNode, Scope>();
+  final _vars = new Map<VariableDeclaration, VarDesc>();
+  Map<TreeNode, List<int>> _temps;
+  Map<TreeNode, VariableDeclaration> _capturedSavedContextVars;
+  Map<TreeNode, VariableDeclaration> _capturedExceptionVars;
+  Map<TreeNode, VariableDeclaration> _capturedStackTraceVars;
+  Map<ForInStatement, VariableDeclaration> _capturedIteratorVars;
   final BytecodeOptions options;
   final TypeEnvironment typeEnvironment;
   final Map<TreeNode, DirectCallMetadata> directCallMetadata;
@@ -155,13 +150,15 @@ class LocalVariables {
   }
 
   VariableDeclaration capturedSavedContextVar(TreeNode node) =>
-      _capturedSavedContextVars[node];
+      _capturedSavedContextVars != null
+          ? _capturedSavedContextVars[node]
+          : null;
   VariableDeclaration capturedExceptionVar(TreeNode node) =>
-      _capturedExceptionVars[node];
+      _capturedExceptionVars != null ? _capturedExceptionVars[node] : null;
   VariableDeclaration capturedStackTraceVar(TreeNode node) =>
-      _capturedStackTraceVars[node];
+      _capturedStackTraceVars != null ? _capturedStackTraceVars[node] : null;
   VariableDeclaration capturedIteratorVar(ForInStatement node) =>
-      _capturedIteratorVars[node];
+      _capturedIteratorVars != null ? _capturedIteratorVars[node] : null;
 
   int get asyncExceptionParamIndexInFrame {
     assert(_currentFrame.isSyncYielding);
@@ -521,12 +518,18 @@ class _ScopeBuilder extends RecursiveVisitor<Null> {
   void _captureSyntheticVariables() {
     int depth = 0;
     for (TreeNode tryBlock in _enclosingTryBlocks) {
+      locals._capturedSavedContextVars ??=
+          new Map<TreeNode, VariableDeclaration>();
       _captureSyntheticVariable(ContinuationVariables.savedTryContextVar(depth),
           tryBlock, locals._capturedSavedContextVars);
       ++depth;
     }
     depth = 0;
     for (TreeNode tryBlock in _enclosingTryCatches) {
+      locals._capturedExceptionVars ??=
+          new Map<TreeNode, VariableDeclaration>();
+      locals._capturedStackTraceVars ??=
+          new Map<TreeNode, VariableDeclaration>();
       _captureSyntheticVariable(ContinuationVariables.exceptionVar(depth),
           tryBlock, locals._capturedExceptionVars);
       _captureSyntheticVariable(ContinuationVariables.stackTraceVar(depth),
@@ -685,6 +688,8 @@ class _ScopeBuilder extends RecursiveVisitor<Null> {
       // Declare a variable to hold 'iterator' so it could be captured.
       iteratorVar = new VariableDeclaration(':iterator');
       _declareVariable(iteratorVar);
+      locals._capturedIteratorVars ??=
+          new Map<ForInStatement, VariableDeclaration>();
       locals._capturedIteratorVars[node] = iteratorVar;
     }
 
@@ -886,6 +891,7 @@ class _Allocator extends RecursiveVisitor<Null> {
   }
 
   void _allocateTemp(TreeNode node, {int count: 1}) {
+    locals._temps ??= new Map<TreeNode, List<int>>();
     assert(locals._temps[node] == null);
     if (_currentScope.tempsUsed + count > _currentFrame.temporaries.length) {
       // Allocate new local slots for temporary variables.
@@ -1143,7 +1149,9 @@ class _Allocator extends RecursiveVisitor<Null> {
   @override
   visitForInStatement(ForInStatement node) {
     _allocateTemp(node);
-    _ensureVariableAllocated(locals._capturedIteratorVars[node]);
+    if (locals._capturedIteratorVars != null) {
+      _ensureVariableAllocated(locals._capturedIteratorVars[node]);
+    }
 
     node.iterable.accept(this);