[vm/aot/tfa] Tree-shake unused libraries

On a large app (which apparently has too many unused dependencies),
size of the AOT kernel file:
before: 464 MB
after: 108 MB

TEST=pkg/vm/testcases/transformations/type_flow/transformer/libraries.dart
Bug: b/287638965
Change-Id: I79a26305c00741babb6a69a18919983b398109e5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310772
Reviewed-by: Slava Egorov <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: alexmarkov

pkg/vm/lib/transformations/type_flow/transformer.dart

@@ -701,6 +701,7 @@ class AnnotateKernel extends RecursiveVisitor {
 class TreeShaker {
   final TypeFlowAnalysis typeFlowAnalysis;
   final bool treeShakeWriteOnlyFields;
+  final Set<Library> _usedLibraries = new Set<Library>();
   final Set<Class> _usedClasses = new Set<Class>();
   final Set<Class> _classesUsedInType = new Set<Class>();
   final Set<Member> _usedMembers = new Set<Member>();
@@ -734,6 +735,7 @@ class TreeShaker {
     _pass2.transformComponent(component);
   }
 
+  bool isLibraryUsed(Library l) => _usedLibraries.contains(l);
   bool isClassReferencedFromNativeCode(Class c) =>
       typeFlowAnalysis.nativeCodeOracle.isClassReferencedFromNativeCode(c);
   bool isClassUsed(Class c) => _usedClasses.contains(c);
@@ -772,6 +774,7 @@ class TreeShaker {
         debugPrint('Class ${c.name} used in type');
       }
       _usedClasses.add(c);
+      _usedLibraries.add(c.enclosingLibrary);
       visitIterable(c.supers, typeVisitor);
       _pass1.transformTypeParameterList(c.typeParameters, c);
       _pass1.transformExpressionList(c.annotations, c);
@@ -794,6 +797,7 @@ class TreeShaker {
         }
         _usedClasses.add(enclosingClass);
       }
+      _usedLibraries.add(m.enclosingLibrary);
 
       FunctionNode? func = null;
       if (m is Field) {
@@ -891,6 +895,7 @@ class TreeShaker {
 
   void addUsedTypedef(Typedef typedef) {
     if (_usedTypedefs.add(typedef)) {
+      _usedLibraries.add(typedef.enclosingLibrary);
       typedef.annotations = const <Expression>[];
       _pass1.transformTypeParameterList(typedef.typeParameters, typedef);
       typedef.type?.accept(typeVisitor);
@@ -1217,6 +1222,19 @@ class _TreeShakerPass1 extends RemovingTransformer {
     return node;
   }
 
+  @override
+  TreeNode visitLoadLibrary(LoadLibrary node, TreeNode? removalSentinel) {
+    shaker._usedLibraries.add(node.import.targetLibrary);
+    return node;
+  }
+
+  @override
+  TreeNode visitCheckLibraryIsLoaded(
+      CheckLibraryIsLoaded node, TreeNode? removalSentinel) {
+    shaker._usedLibraries.add(node.import.targetLibrary);
+    return node;
+  }
+
   @override
   TreeNode visitInstanceInvocation(
       InstanceInvocation node, TreeNode? removalSentinel) {
@@ -1727,8 +1745,44 @@ class _TreeShakerPass2 extends RemovingTransformer {
     }
   }
 
+  final _libraryExportDeps = <Library, Set<Library>>{};
+  final _additionalDeps = <Library>{};
+
+  // Returns set of export dependencies of given library.
+  Set<Library> getLibraryExportDeps(Library node) =>
+      _libraryExportDeps[node] ??= calculateLibraryExportDeps(node);
+
+  Set<Library> calculateLibraryExportDeps(Library node) {
+    final processed = <Library>{};
+    final worklist = <Library>[];
+    final deps = <Library>{};
+    worklist.add(node);
+    processed.add(node);
+    while (worklist.isNotEmpty) {
+      final lib = worklist.removeLast();
+      for (final dep in lib.dependencies) {
+        if (!dep.isExport) {
+          continue;
+        }
+        final targetLibrary = dep.targetLibrary;
+        if (processed.add(targetLibrary)) {
+          if (shaker.isLibraryUsed(targetLibrary)) {
+            deps.add(targetLibrary);
+          } else {
+            worklist.add(targetLibrary);
+          }
+        }
+      }
+    }
+    return deps;
+  }
+
   @override
   TreeNode visitLibrary(Library node, TreeNode? removalSentinel) {
+    if (!shaker.isLibraryUsed(node) && node.importUri.scheme != 'dart') {
+      return removalSentinel!;
+    }
+    _additionalDeps.clear();
     node.transformOrRemoveChildren(this);
     // The transformer API does not iterate over `Library.additionalExports`,
     // so we manually delete the references to shaken nodes.
@@ -1746,6 +1800,29 @@ class _TreeShakerPass2 extends RemovingTransformer {
         return !shaker.isMemberUsed(node as Member);
       }
     });
+    // Add transitive export dependencies of the removed imported libraries.
+    // This is needed to maintain connected library graph
+    // which is critical for calculation of the deferred loading units.
+    if (_additionalDeps.isNotEmpty) {
+      for (final dep in node.dependencies) {
+        _additionalDeps.remove(dep.targetLibrary);
+      }
+      for (final lib in _additionalDeps) {
+        node.addDependency(LibraryDependency.import(lib));
+      }
+      _additionalDeps.clear();
+    }
+    return node;
+  }
+
+  @override
+  TreeNode visitLibraryDependency(
+      LibraryDependency node, TreeNode? removalSentinel) {
+    final targetLibrary = node.targetLibrary;
+    if (!shaker.isLibraryUsed(targetLibrary)) {
+      _additionalDeps.addAll(getLibraryExportDeps(targetLibrary));
+      return removalSentinel!;
+    }
     return node;
   }
 
@@ -1991,6 +2068,10 @@ class _TreeShakerConstantVisitor extends ConstantVisitor<Null> {
 
   @override
   visitSymbolConstant(SymbolConstant constant) {
+    final libraryRef = constant.libraryReference;
+    if (libraryRef != null) {
+      shaker._usedLibraries.add(libraryRef.asLibrary);
+    }
     // The Symbol class and it's _name field are always retained.
   }
 

pkg/vm/testcases/transformations/type_flow/transformer/const_default.dart.expect

@@ -1,11 +1,6 @@
 library #lib;
 import self as self;
 
-import "file:pkg/vm/testcases/transformations/type_flow/transformer/const_default.lib.dart";
-
 static method main() → dynamic {
   has-declared-initializer dynamic dyn = null;
 }
-library const_default.lib.dart;
-import self as self;
-

pkg/vm/testcases/transformations/type_flow/transformer/libraries.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'libraries_lib1.lib.dart';
+import 'libraries_lib2.lib.dart';
+import 'libraries_lib3.lib.dart';
+
+void unused() {
+  print(Foo1());
+  print(bar1());
+}
+
+void used() {
+  print(Foo2());
+  print(bar2());
+  print(privateSymbol);
+}
+
+main() {
+  used();
+}

pkg/vm/testcases/transformations/type_flow/transformer/libraries.dart.expect

@@ -0,0 +1,33 @@
+library #lib;
+import self as self;
+import "dart:core" as core;
+import "libraries_lib2.lib.dart" as lib;
+
+import "file:pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib2.lib.dart";
+import "file:pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib3.lib.dart";
+
+static method used() → void {
+  core::print(new lib::Foo2::•());
+  core::print([@vm.inferred-type.metadata=dart.core::_OneByteString (value: "hi")] lib::bar2());
+  core::print(#C1);
+}
+static method main() → dynamic {
+  self::used();
+}
+constants  {
+  #C1 = #file:pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib3.lib.dart::_bazz
+}
+library libraries_lib2.lib.dart;
+import self as self;
+import "dart:core" as core;
+
+class Foo2 extends core::Object {
+  synthetic constructor •() → self::Foo2
+    : super core::Object::•()
+    ;
+}
+static method bar2() → core::String
+  return "hi";
+library libraries_lib3.lib.dart;
+import self as self;
+

pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib1.lib.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class Foo1 {}
+
+String bar1() => 'bye';

pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib2.lib.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class Foo2 {}
+
+String bar2() => 'hi';

pkg/vm/testcases/transformations/type_flow/transformer/libraries_lib3.lib.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+const privateSymbol = #_bazz;

pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/create_test.dart.expect

@@ -5,8 +5,17 @@ import "dart:core" as core;
 import "package:test_core/scaffolding.dart" as sca;
 import "package:matcher/src/expect/expect.dart" as exp;
 
-import "package:test/test.dart";
 import "file:pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/generated/foo.pb.dart";
+import "package:matcher/src/expect/expect.dart";
+import "package:test_api/hooks.dart";
+import "package:test_core/scaffolding.dart";
+import "package:matcher/src/core_matchers.dart";
+import "package:matcher/src/description.dart";
+import "package:matcher/src/equals_matcher.dart";
+import "package:matcher/src/interfaces.dart";
+import "package:matcher/src/operator_matchers.dart";
+import "package:matcher/src/type_matcher.dart";
+import "package:matcher/src/util.dart";
 
 static method main() → dynamic {
   pb::FooKeep foo = let final pb::FooKeep #t1 = [@vm.inferred-type.metadata=library file:pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/generated/foo.pb.dart::FooKeep] pb::FooKeep::•() in block {

pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/decode_test.dart.expect

@@ -5,8 +5,17 @@ import "package:test_core/scaffolding.dart" as sca;
 import "package:matcher/src/expect/expect.dart" as exp;
 import "dart:core" as core;
 
-import "package:test/test.dart";
 import "file:pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/generated/foo.pb.dart";
+import "package:matcher/src/expect/expect.dart";
+import "package:test_api/hooks.dart";
+import "package:test_core/scaffolding.dart";
+import "package:matcher/src/core_matchers.dart";
+import "package:matcher/src/description.dart";
+import "package:matcher/src/equals_matcher.dart";
+import "package:matcher/src/interfaces.dart";
+import "package:matcher/src/operator_matchers.dart";
+import "package:matcher/src/type_matcher.dart";
+import "package:matcher/src/util.dart";
 
 [@vm.inferred-type.metadata=dart.core::_GrowableList<dart.core::int>]static field core::List<core::int> buffer = <core::int>[10, 4, 8, 5, 16, 4, 26, 9, 10, 3, 102, 111, 111, 18, 2, 8, 42, 34, 9, 10, 3, 122, 111, 112, 18, 2, 8, 3, 40, 43, 50, 0, 58, 0];
 static method main() → dynamic {

pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/freeze_test.dart.expect

@@ -7,8 +7,18 @@ import "package:protobuf/protobuf.dart" as pro;
 import "package:matcher/src/expect/expect.dart" as exp;
 import "package:matcher/src/expect/throws_matcher.dart" as thr;
 
-import "package:test/test.dart";
 import "file:pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/generated/foo.pb.dart";
+import "package:matcher/src/expect/expect.dart";
+import "package:matcher/src/expect/throws_matcher.dart";
+import "package:test_api/hooks.dart";
+import "package:test_core/scaffolding.dart";
+import "package:matcher/src/core_matchers.dart";
+import "package:matcher/src/description.dart";
+import "package:matcher/src/equals_matcher.dart";
+import "package:matcher/src/interfaces.dart";
+import "package:matcher/src/operator_matchers.dart";
+import "package:matcher/src/type_matcher.dart";
+import "package:matcher/src/util.dart";
 
 static method main() → dynamic {
   pb::FooKeep foo = let final pb::FooKeep #t1 = [@vm.inferred-type.metadata=library file:pkg/vm/testcases/transformations/type_flow/transformer/protobuf_handler/lib/generated/foo.pb.dart::FooKeep] pb::FooKeep::•() in block {