[vm/nnbd] Further specialize invocations of List.filled factory

If 'growable' argument of List.filled factory invocation is known at
compile time we can replace it with more specialized constructors
creating growable or fixed-size lists. This results in a more accurate
inferred type and more efficient code which uses the created list.

Fixes dart-lang/sdk#42551

Change-Id: I427e1bdb8a0f2a83410a9533050d19cbca2d27d6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153064
Reviewed-by: Vyacheslav Egorov <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>

Author: alexmarkov

pkg/front_end/lib/src/fasta/source/source_loader.dart

@@ -1300,10 +1300,12 @@ class List<E> extends Iterable {
 
 class _GrowableList<E> {
   factory _GrowableList() => null;
+  factory _GrowableList.filled() => null;
 }
 
 class _List<E> {
   factory _List() => null;
+  factory _List.filled() => null;
 }
 
 class MapEntry<K, V> {

pkg/vm/lib/transformations/list_factory_specializer.dart

@@ -13,13 +13,17 @@ import 'package:kernel/core_types.dart' show CoreTypes;
 /// new List() => new _GrowableList(0)
 /// new List(n) => new _List(n)
 /// new List.filled(n, null, growable: true) => new _GrowableList(n)
+/// new List.filled(n, x, growable: true) => new _GrowableList.filled(n, x)
 /// new List.filled(n, null) => new _List(n)
+/// new List.filled(n, x) => new _List.filled(n, x)
 ///
 class ListFactorySpecializer {
   final Procedure _defaultListFactory;
   final Procedure _listFilledFactory;
   final Procedure _growableListFactory;
+  final Procedure _growableListFilledFactory;
   final Procedure _fixedListFactory;
+  final Procedure _fixedListFilledFactory;
 
   ListFactorySpecializer(CoreTypes coreTypes)
       : _defaultListFactory =
@@ -28,12 +32,17 @@ class ListFactorySpecializer {
             coreTypes.index.getMember('dart:core', 'List', 'filled'),
         _growableListFactory =
             coreTypes.index.getMember('dart:core', '_GrowableList', ''),
-        _fixedListFactory =
-            coreTypes.index.getMember('dart:core', '_List', '') {
+        _growableListFilledFactory =
+            coreTypes.index.getMember('dart:core', '_GrowableList', 'filled'),
+        _fixedListFactory = coreTypes.index.getMember('dart:core', '_List', ''),
+        _fixedListFilledFactory =
+            coreTypes.index.getMember('dart:core', '_List', 'filled') {
     assert(_defaultListFactory.isFactory);
     assert(_listFilledFactory.isFactory);
     assert(_growableListFactory.isFactory);
+    assert(_growableListFilledFactory.isFactory);
     assert(_fixedListFactory.isFactory);
+    assert(_fixedListFilledFactory.isFactory);
   }
 
   TreeNode transformStaticInvocation(StaticInvocation node) {
@@ -53,10 +62,8 @@ class ListFactorySpecializer {
       assert(args.positional.length == 2);
       final length = args.positional[0];
       final fill = args.positional[1];
-      if (fill is! NullLiteral &&
-          !(fill is ConstantExpression && fill.constant is NullConstant)) {
-        return node;
-      }
+      final fillingWithNull = fill is NullLiteral ||
+          (fill is ConstantExpression && fill.constant is NullConstant);
       bool growable;
       if (args.named.isEmpty) {
         growable = false;
@@ -78,13 +85,25 @@ class ListFactorySpecializer {
         }
       }
       if (growable) {
-        return StaticInvocation(
-            _growableListFactory, Arguments([length], types: args.types))
-          ..fileOffset = node.fileOffset;
+        if (fillingWithNull) {
+          return StaticInvocation(
+              _growableListFactory, Arguments([length], types: args.types))
+            ..fileOffset = node.fileOffset;
+        } else {
+          return StaticInvocation(_growableListFilledFactory,
+              Arguments([length, fill], types: args.types))
+            ..fileOffset = node.fileOffset;
+        }
       } else {
-        return StaticInvocation(
-            _fixedListFactory, Arguments([length], types: args.types))
-          ..fileOffset = node.fileOffset;
+        if (fillingWithNull) {
+          return StaticInvocation(
+              _fixedListFactory, Arguments([length], types: args.types))
+            ..fileOffset = node.fileOffset;
+        } else {
+          return StaticInvocation(_fixedListFilledFactory,
+              Arguments([length, fill], types: args.types))
+            ..fileOffset = node.fileOffset;
+        }
       }
     }
 

runtime/vm/compiler/recognized_methods_list.h

@@ -444,8 +444,11 @@ namespace dart {
 //  result-cid, fingerprint).
 #define RECOGNIZED_LIST_FACTORY_LIST(V)                                        \
   V(_ListFactory, _List, ., kArrayCid, 0x03ddbd3a)                             \
+  V(_ListFilledFactory, _List, .filled, kArrayCid, 0x0)                        \
   V(_GrowableListWithData, _GrowableList, ._withData, kGrowableObjectArrayCid, \
     0x5cfd6a7f)                                                                \
+  V(_GrowableListFilledFactory, _GrowableList, .filled,                        \
+    kGrowableObjectArrayCid, 0x0)                                              \
   V(_GrowableListFactory, _GrowableList, ., kGrowableObjectArrayCid,           \
     0x3eed680b)                                                                \
   V(_Int8ArrayFactory, Int8List, ., kTypedDataInt8ArrayCid, 0x6ce2f102)        \

runtime/vm/symbols.h

@@ -361,6 +361,7 @@ class ObjectPointerVisitor;
   V(_FutureListener, "_FutureListener")                                        \
   V(_GrowableList, "_GrowableList")                                            \
   V(_GrowableListFactory, "_GrowableList.")                                    \
+  V(_GrowableListFilledFactory, "_GrowableList.filled")                        \
   V(_GrowableListWithData, "_GrowableList._withData")                          \
   V(_ImmutableList, "_ImmutableList")                                          \
   V(_Int16ArrayFactory, "Int16List.")                                          \
@@ -388,6 +389,7 @@ class ObjectPointerVisitor;
   V(_LinkedHashSet, "_CompactLinkedHashSet")                                   \
   V(_List, "_List")                                                            \
   V(_ListFactory, "_List.")                                                    \
+  V(_ListFilledFactory, "_List.filled")                                        \
   V(_MethodMirror, "_MethodMirror")                                            \
   V(_Mint, "_Mint")                                                            \
   V(_MirrorReference, "_MirrorReference")                                      \

sdk/lib/_internal/vm/lib/array.dart

@@ -11,6 +11,18 @@ class _List<E> extends FixedLengthListBase<E> {
   @pragma("vm:prefer-inline")
   factory _List(length) native "List_allocate";
 
+  // Specialization of List.filled constructor for growable == false.
+  // Used by pkg/vm/lib/transformations/list_factory_specializer.dart.
+  factory _List.filled(int length, E fill) {
+    final result = _List<E>(length);
+    if (fill != null) {
+      for (int i = 0; i < result.length; i++) {
+        result[i] = fill;
+      }
+    }
+    return result;
+  }
+
   E operator [](int index) native "List_getIndexed";
 
   void operator []=(int index, E value) {

sdk/lib/_internal/vm/lib/growable_array.dart

@@ -107,6 +107,18 @@ class _GrowableList<T> extends ListBase<T> {
     return new _GrowableList<T>._withData(data);
   }
 
+  // Specialization of List.filled constructor for growable == true.
+  // Used by pkg/vm/lib/transformations/list_factory_specializer.dart.
+  factory _GrowableList.filled(int length, T fill) {
+    final result = _GrowableList<T>(length);
+    if (fill != null) {
+      for (int i = 0; i < result.length; i++) {
+        result[i] = fill;
+      }
+    }
+    return result;
+  }
+
   @pragma("vm:exact-result-type",
       <dynamic>[_GrowableList, "result-type-uses-passed-type-arguments"])
   factory _GrowableList._withData(_List data) native "GrowableList_allocate";