[vm,bytecode] Store offsets in bytecode declarations, remove putIfAbsent

Instead of keeping offsets of bytecode declarations in a map,
offset is now stored in a field of a base class for all declarations.
This saves certain number of map lookups while serializing bytecode.
Also, calls to a rather expensive Map.putIfAbsent are removed.

Change-Id: I036fbb0e1d8afc6e402709a0a1eafb0e50a2c25a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/122170
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov

pkg/vm/lib/bytecode/bytecode_serialization.dart

@@ -229,12 +229,13 @@ class BufferedReader {
     return result;
   }
 
-  T readLinkOffset<T>() {
+  T readLinkOffset<T extends BytecodeDeclaration>() {
     final offset = readPackedUInt30();
     return linkReader.get<T>(offset);
   }
 
-  ForwardReference<T> readLinkOffsetAsForwardReference<T>() {
+  ForwardReference<T>
+      readLinkOffsetAsForwardReference<T extends BytecodeDeclaration>() {
     final offset = readPackedUInt30();
     return new ForwardReference<T>(offset, linkReader);
   }
@@ -429,24 +430,26 @@ class SLEB128DeltaDecoder {
   }
 }
 
-class LinkWriter {
-  final _map = <Object, int>{};
+class BytecodeDeclaration {
+  int _offset;
+}
 
-  void put(Object target, int offset) {
-    _map[target] = offset;
+class LinkWriter {
+  void put(BytecodeDeclaration target, int offset) {
+    target._offset = offset;
   }
 
-  int getOffset(Object target) {
-    return _map[target] ??
+  int getOffset(BytecodeDeclaration target) {
+    return target._offset ??
         (throw 'Offset of ${target.runtimeType} $target is not set');
   }
 }
 
 class LinkReader {
-  final _map = <Type, Map<int, Object>>{};
+  final _map = <Type, Map<int, BytecodeDeclaration>>{};
 
-  void setOffset<T>(T target, int offset) {
-    final offsetToObject = (_map[T] ??= <int, Object>{});
+  void setOffset<T>(BytecodeDeclaration target, int offset) {
+    final offsetToObject = (_map[T] ??= <int, BytecodeDeclaration>{});
     final previous = offsetToObject[offset];
     if (previous != null) {
       throw 'Unable to associate offset $T/$offset with ${target.runtimeType} $target.'
@@ -455,13 +458,13 @@ class LinkReader {
     offsetToObject[offset] = target;
   }
 
-  T get<T>(int offset) {
+  T get<T extends BytecodeDeclaration>(int offset) {
     return _map[T][offset] ?? (throw 'No object at offset $T/$offset');
   }
 }
 
 // Placeholder for an object which will be read in future.
-class ForwardReference<T> {
+class ForwardReference<T extends BytecodeDeclaration> {
   final int offset;
   final LinkReader linkReader;
 

pkg/vm/lib/bytecode/constant_pool.dart

@@ -829,14 +829,16 @@ class ConstantPool {
           isSetter: invocationKind == InvocationKind.setter)));
 
   int _add(ConstantPoolEntry entry) {
-    return _canonicalizationCache.putIfAbsent(entry, () {
-      int index = entries.length;
+    int index = _canonicalizationCache[entry];
+    if (index == null) {
+      index = entries.length;
       if (index >= constantPoolIndexLimit) {
         throw new ConstantPoolIndexOverflowException();
       }
       _addEntry(entry);
-      return index;
-    });
+      _canonicalizationCache[entry] = index;
+    }
+    return index;
   }
 
   void _addEntry(ConstantPoolEntry entry) {

pkg/vm/lib/bytecode/declarations.dart

@@ -6,7 +6,12 @@ library vm.bytecode.declarations;
 
 import 'package:kernel/ast.dart';
 import 'bytecode_serialization.dart'
-    show BufferedWriter, BufferedReader, BytecodeSizeStatistics, StringTable;
+    show
+        BufferedWriter,
+        BufferedReader,
+        BytecodeDeclaration,
+        BytecodeSizeStatistics,
+        StringTable;
 import 'constant_pool.dart' show ConstantPool;
 import 'dbc.dart' show currentBytecodeFormatVersion;
 import 'disassembler.dart' show BytecodeDisassembler;
@@ -15,7 +20,7 @@ import 'local_variable_table.dart' show LocalVariableTable;
 import 'object_table.dart' show ObjectTable, ObjectHandle, NameAndType;
 import 'source_positions.dart' show LineStarts, SourcePositions;
 
-class LibraryDeclaration {
+class LibraryDeclaration extends BytecodeDeclaration {
   static const usesDartMirrorsFlag = 1 << 0;
   static const usesDartFfiFlag = 1 << 1;
   static const hasExtensionsFlag = 1 << 2;
@@ -89,7 +94,7 @@ class LibraryDeclaration {
   }
 }
 
-class ClassDeclaration {
+class ClassDeclaration extends BytecodeDeclaration {
   static const isAbstractFlag = 1 << 0;
   static const isEnumFlag = 1 << 1;
   static const hasTypeParamsFlag = 1 << 2;
@@ -220,7 +225,7 @@ class ClassDeclaration {
   }
 }
 
-class SourceFile {
+class SourceFile extends BytecodeDeclaration {
   static const hasLineStartsFlag = 1 << 0;
   static const hasSourceFlag = 1 << 1;
 
@@ -274,7 +279,7 @@ class SourceFile {
   }
 }
 
-class Members {
+class Members extends BytecodeDeclaration {
   final List<FieldDeclaration> fields;
   final List<FunctionDeclaration> functions;
 
@@ -789,7 +794,7 @@ class ParameterDeclaration {
   String toString() => '$type $name';
 }
 
-class Code {
+class Code extends BytecodeDeclaration {
   static const hasExceptionsTableFlag = 1 << 0;
   static const hasSourcePositionsFlag = 1 << 1;
   static const hasNullableFieldsFlag = 1 << 2;
@@ -1190,7 +1195,7 @@ class ClosureCode {
   }
 }
 
-class AnnotationsDeclaration {
+class AnnotationsDeclaration extends BytecodeDeclaration {
   final ObjectHandle object;
 
   AnnotationsDeclaration(this.object);

pkg/vm/lib/bytecode/local_variable_table.dart

@@ -128,7 +128,7 @@ class ContextVariable extends LocalVariableEntry {
 }
 
 /// Keeps information about declared local variables.
-class LocalVariableTable {
+class LocalVariableTable extends BytecodeDeclaration {
   final scopes = <Scope>[];
   final activeScopes = <Scope>[];
   ContextVariable contextVariable;

pkg/vm/lib/bytecode/object_table.dart

@@ -1877,11 +1877,13 @@ class ObjectTable implements ObjectWriter, ObjectReader {
 
   ObjectHandle getOrAddObject(ObjectHandle obj) {
     assert(obj._useCount == 0);
-    ObjectHandle canonical = _canonicalizationCache.putIfAbsent(obj, () {
+    ObjectHandle canonical = _canonicalizationCache[obj];
+    if (canonical == null) {
       assert(_indexTable == null);
       _objects.add(obj);
-      return obj;
-    });
+      _canonicalizationCache[obj] = obj;
+      canonical = obj;
+    }
     ++canonical._useCount;
     return canonical;
   }

pkg/vm/lib/bytecode/source_positions.dart

@@ -8,13 +8,14 @@ import 'bytecode_serialization.dart'
     show
         BufferedWriter,
         BufferedReader,
+        BytecodeDeclaration,
         PackedUInt30DeltaEncoder,
         PackedUInt30DeltaDecoder,
         SLEB128DeltaEncoder,
         SLEB128DeltaDecoder;
 
 /// Maintains mapping between bytecode instructions and source positions.
-class SourcePositions {
+class SourcePositions extends BytecodeDeclaration {
   // Special value of fileOffset which marks synthetic code without source
   // position.
   static const syntheticCodeMarker = -1;
@@ -99,7 +100,7 @@ class SourcePositions {
 
 /// Keeps file offsets of line starts. This information is used to
 /// decode source positions to line/column.
-class LineStarts {
+class LineStarts extends BytecodeDeclaration {
   final List<int> lineStarts;
 
   LineStarts(this.lineStarts);