Add option to run wasm-opt on module output. (#124831)

This fixes https://github.com/flutter/flutter/issues/124159

Adds the command line argument `--wasm-opt` to optimize the web assembly output.

packages/flutter_tools/lib/src/artifacts.dart

@@ -43,6 +43,8 @@ enum Artifact {
   dart2jsSnapshot,
   /// The dart snapshot of the dart2wasm compiler.
   dart2wasmSnapshot,
+  /// The wasm-opt binary that ships with the dart-sdk
+  wasmOptBinary,
 
   /// The root of the Linux desktop sources.
   linuxDesktopPath,
@@ -184,6 +186,8 @@ String? _artifactToFileName(Artifact artifact, Platform hostPlatform, [ BuildMod
       return 'dart2js.dart.snapshot';
     case Artifact.dart2wasmSnapshot:
       return 'dart2wasm_product.snapshot';
+    case Artifact.wasmOptBinary:
+      return 'wasm-opt$exe';
     case Artifact.frontendServerSnapshotForEngineDartSdk:
       return 'frontend_server.dart.snapshot';
     case Artifact.linuxDesktopPath:
@@ -510,6 +514,7 @@ class CachedArtifacts implements Artifacts {
       case Artifact.engineDartAotRuntime:
       case Artifact.dart2jsSnapshot:
       case Artifact.dart2wasmSnapshot:
+      case Artifact.wasmOptBinary:
       case Artifact.frontendServerSnapshotForEngineDartSdk:
       case Artifact.constFinder:
       case Artifact.flutterFramework:
@@ -550,6 +555,7 @@ class CachedArtifacts implements Artifacts {
       case Artifact.engineDartAotRuntime:
       case Artifact.dart2jsSnapshot:
       case Artifact.dart2wasmSnapshot:
+      case Artifact.wasmOptBinary:
       case Artifact.frontendServerSnapshotForEngineDartSdk:
       case Artifact.constFinder:
       case Artifact.flutterMacOSFramework:
@@ -608,6 +614,7 @@ class CachedArtifacts implements Artifacts {
       case Artifact.engineDartAotRuntime:
       case Artifact.dart2jsSnapshot:
       case Artifact.dart2wasmSnapshot:
+      case Artifact.wasmOptBinary:
       case Artifact.frontendServerSnapshotForEngineDartSdk:
       case Artifact.icuData:
       case Artifact.isolateSnapshotData:
@@ -646,6 +653,11 @@ class CachedArtifacts implements Artifacts {
           _dartSdkPath(_cache), 'bin', 'snapshots',
           _artifactToFileName(artifact, _platform),
         );
+      case Artifact.wasmOptBinary:
+        return _fileSystem.path.join(
+          _dartSdkPath(_cache), 'bin', 'utils',
+          _artifactToFileName(artifact, _platform),
+        );
       case Artifact.flutterTester:
       case Artifact.vmSnapshotData:
       case Artifact.isolateSnapshotData:
@@ -963,6 +975,8 @@ class CachedLocalEngineArtifacts implements Artifacts {
       case Artifact.dart2wasmSnapshot:
       case Artifact.frontendServerSnapshotForEngineDartSdk:
         return _fileSystem.path.join(_getDartSdkPath(), 'bin', 'snapshots', artifactFileName);
+      case Artifact.wasmOptBinary:
+        return _fileSystem.path.join(_getDartSdkPath(), 'bin', 'utils', artifactFileName);
       case Artifact.flutterToolsFileGenerators:
         return _getFileGeneratorsPath();
     }
@@ -1092,6 +1106,11 @@ class CachedLocalWebSdkArtifacts implements Artifacts {
             _getDartSdkPath(), 'bin', 'snapshots',
             _artifactToFileName(artifact, _platform, mode),
           );
+        case Artifact.wasmOptBinary:
+          return _fileSystem.path.join(
+            _getDartSdkPath(), 'bin', 'snapshots',
+            _artifactToFileName(artifact, _platform, mode),
+          );
         case Artifact.genSnapshot:
         case Artifact.flutterTester:
         case Artifact.flutterFramework:

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -242,9 +242,12 @@ class Dart2WasmTarget extends Dart2WebTarget {
     if (buildModeEnvironment == null) {
       throw MissingDefineException(kBuildMode, name);
     }
+    final WasmCompilerConfig compilerConfig = WasmCompilerConfig.fromBuildSystemEnvironment(environment.defines);
     final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
     final Artifacts artifacts = globals.artifacts!;
-    final File outputWasmFile = environment.buildDir.childFile('main.dart.wasm');
+    final File outputWasmFile = environment.buildDir.childFile(
+      compilerConfig.runWasmOpt ? 'main.dart.unopt.wasm' : 'main.dart.wasm'
+    );
     final File depFile = environment.buildDir.childFile('dart2wasm.d');
     final String dartSdkPath = artifacts.getArtifactPath(Artifact.engineDartSdkPath, platform: TargetPlatform.web_javascript);
     final String dartSdkRoot = environment.fileSystem.directory(dartSdkPath).parent.path;
@@ -260,7 +263,7 @@ class Dart2WasmTarget extends Dart2WebTarget {
       ...decodeCommaSeparated(environment.defines, kExtraFrontEndOptions),
       for (final String dartDefine in decodeDartDefines(environment.defines, kDartDefines))
         '-D$dartDefine',
-      ...WasmCompilerConfig.fromBuildSystemEnvironment(environment.defines).toCommandOptions(),
+      ...compilerConfig.toCommandOptions(),
       '--packages=.dart_tool/package_config.json',
       '--dart-sdk=$dartSdkPath',
       '--multi-root-scheme',
@@ -286,6 +289,35 @@ class Dart2WasmTarget extends Dart2WebTarget {
     if (compileResult.exitCode != 0) {
       throw Exception(_collectOutput(compileResult));
     }
+    if (compilerConfig.runWasmOpt) {
+      final String wasmOptBinary = artifacts.getArtifactPath(
+        Artifact.wasmOptBinary,
+        platform: TargetPlatform.web_javascript
+      );
+      final File optimizedOutput = environment.buildDir.childFile('main.dart.wasm');
+      final List<String> optimizeArgs = <String>[
+        wasmOptBinary,
+        '-all',
+        '--closed-world',
+        '-tnh',
+        '-O3',
+        '--type-ssa',
+        '--gufa',
+        '-O3',
+        '--type-merging',
+        outputWasmFile.path,
+        '-o',
+        optimizedOutput.path,
+      ];
+      final ProcessResult optimizeResult = await globals.processManager.run(optimizeArgs);
+      if (optimizeResult.exitCode != 0) {
+        throw Exception(_collectOutput(optimizeResult));
+      }
+
+      // Rename the .mjs file not to have the `.unopt` bit
+      final File jsRuntimeFile = environment.buildDir.childFile('main.dart.unopt.mjs');
+      await jsRuntimeFile.rename(environment.buildDir.childFile('main.dart.mjs').path);
+    }
   }
 
   @override

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -101,6 +101,12 @@ class BuildWebCommand extends BuildSubCommand {
       negatable: false,
       hide: !featureFlags.isFlutterWebWasmEnabled,
     );
+    argParser.addFlag(
+      'wasm-opt',
+      help: 'Run wasm-opt on the output wasm module.',
+      negatable: false,
+      hide: !featureFlags.isFlutterWebWasmEnabled,
+    );
   }
 
   final FileSystem _fileSystem;
@@ -133,6 +139,7 @@ class BuildWebCommand extends BuildSubCommand {
       }
       compilerConfig = WasmCompilerConfig(
         omitTypeChecks: boolArg('omit-type-checks'),
+        runWasmOpt: boolArg('wasm-opt'),
       );
     } else {
       compilerConfig = JsCompilerConfig(

packages/flutter_tools/lib/src/web/compiler_config.dart

@@ -130,6 +130,7 @@ class JsCompilerConfig extends WebCompilerConfig {
 class WasmCompilerConfig extends WebCompilerConfig {
   const WasmCompilerConfig({
     required this.omitTypeChecks,
+    required this.runWasmOpt,
   });
 
   /// Creates a new [WasmCompilerConfig] from build system environment values.
@@ -139,20 +140,26 @@ class WasmCompilerConfig extends WebCompilerConfig {
           Map<String, String> defines) =>
       WasmCompilerConfig(
         omitTypeChecks: defines[kOmitTypeChecks] == 'true',
+        runWasmOpt: defines[kRunWasmOpt] == 'true',
       );
 
   /// Build environment for [omitTypeChecks];
   static const String kOmitTypeChecks = 'WasmOmitTypeChecks';
+  static const String kRunWasmOpt = 'RunWasmOpt';
 
   /// If `omit-type-checks` should be passed to `dart2wasm`.
   final bool omitTypeChecks;
 
+  // Run wasm-opt on the resulting module.
+  final bool runWasmOpt;
+
   @override
   bool get isWasm => true;
 
   @override
   Map<String, String> toBuildSystemEnvironment() => <String, String>{
     kOmitTypeChecks: omitTypeChecks.toString(),
+    kRunWasmOpt: runWasmOpt.toString(),
   };
 
   List<String> toCommandOptions() => <String>[

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -845,6 +845,62 @@ void main() {
     ProcessManager: () => processManager,
   }));
 
+  test('Dart2WasmTarget invokes dart2wasm and wasm-opt when RunWasmOpt is enabled', () => testbed.run(() async {
+    environment.defines[kBuildMode] = 'release';
+    environment.defines[WasmCompilerConfig.kRunWasmOpt] = 'true';
+
+    final File depFile = environment.buildDir.childFile('dart2wasm.d');
+
+    final File outputJsFile = environment.buildDir.childFile('main.dart.unopt.mjs');
+    processManager.addCommand(FakeCommand(
+      command: <String>[
+        'bin/cache/dart-sdk/bin/dartaotruntime',
+        '--disable-dart-dev',
+        'bin/cache/dart-sdk/bin/snapshots/dart2wasm_product.snapshot',
+        '-Ddart.vm.product=true',
+        '--packages=.dart_tool/package_config.json',
+        '--dart-sdk=bin/cache/dart-sdk',
+        '--multi-root-scheme',
+        'org-dartlang-sdk',
+        '--multi-root',
+        'bin/cache/flutter_web_sdk',
+        '--multi-root',
+        'bin/cache',
+        '--libraries-spec',
+        'bin/cache/flutter_web_sdk/libraries.json',
+        '--depfile=${depFile.absolute.path}',
+
+        environment.buildDir.childFile('main.dart').absolute.path,
+        environment.buildDir.childFile('main.dart.unopt.wasm').absolute.path,
+      ], onRun: () => outputJsFile..createSync()..writeAsStringSync('foo')));
+
+      processManager.addCommand(FakeCommand(
+        command: <String>[
+          'bin/cache/dart-sdk/bin/utils/wasm-opt',
+          '-all',
+          '--closed-world',
+          '-tnh',
+          '-O3',
+          '--type-ssa',
+          '--gufa',
+          '-O3',
+          '--type-merging',
+          environment.buildDir.childFile('main.dart.unopt.wasm').absolute.path,
+          '-o',
+          environment.buildDir.childFile('main.dart.wasm').absolute.path,
+        ]));
+
+    await Dart2WasmTarget(WebRendererMode.canvaskit).build(environment);
+
+    expect(outputJsFile.existsSync(), isFalse);
+    final File movedJsFile = environment.buildDir.childFile('main.dart.mjs');
+    expect(movedJsFile.existsSync(), isTrue);
+    expect(movedJsFile.readAsStringSync(), 'foo');
+  }, overrides: <Type, Generator>{
+    ProcessManager: () => processManager,
+  }));
+
+
   test('Dart2WasmTarget with skwasm renderer adds extra flags', () => testbed.run(() async {
     environment.defines[kBuildMode] = 'release';
     final File depFile = environment.buildDir.childFile('dart2wasm.d');

packages/flutter_tools/test/general.shard/web/compile_web_test.dart

@@ -47,6 +47,7 @@ void main() {
         'HasWebPlugins': 'false',
         'ServiceWorkerStrategy': ServiceWorkerStrategy.offlineFirst.cliName,
         'WasmOmitTypeChecks': 'false',
+        'RunWasmOpt': 'false',
         'BuildMode': 'debug',
         'DartObfuscation': 'false',
         'TrackWidgetCreation': 'true',
@@ -70,7 +71,10 @@ void main() {
       'target',
       BuildInfo.debug,
       ServiceWorkerStrategy.offlineFirst,
-      compilerConfig: const WasmCompilerConfig(omitTypeChecks: false),
+      compilerConfig: const WasmCompilerConfig(
+        omitTypeChecks: false,
+        runWasmOpt: false
+      ),
     );
 
     expect(logger.statusText, contains('Compiling target for the Web...'));