[dart2wasm] Add wasm module printing functionality.

This adds support for printing module IR as text format.
For convenience we add a `pkg/dart2wasm/bin/wami.dart` that
produces very similar output to V8's `wami`.

The goal is to use this to write size/perf optimization tests
by dumping IR into expectation files (will add this
infrastructure in a future CL)

Issue #60928

Change-Id: I42d19c2b8c6242f55693d6ed5d844a5c1ecb1f39
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/454600
Commit-Queue: Martin Kustermann <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>

Author: mkustermann

pkg/dart2wasm/bin/wasm2wat.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2025, 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 'dart:io';
+
+import 'package:wasm_builder/wasm_builder.dart';
+
+void main(List<String> args) {
+  final input = args[0];
+  final wasmBytes = File(input).readAsBytesSync();
+
+  final deserializer = Deserializer(wasmBytes);
+  final module = Module.deserialize(deserializer);
+  print(module.printAsWat());
+}

pkg/dart2wasm/test/wasm2wat_test.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2025, 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 'dart:io';
+import 'dart:typed_data';
+
+import 'package:path/path.dart' as path;
+import 'package:wasm_builder/wasm_builder.dart';
+
+import 'self_compile_test.dart' show withTempDir, run;
+
+Future main() async {
+  if (!Platform.isLinux && !Platform.isMacOS) return;
+
+  await withTempDir((String tempDir) async {
+    final dartFilename = 'third_party/flute/benchmarks/lib/complex.dart';
+
+    final wasmFilename = path.join(tempDir, 'flute.wasm');
+    final optWasmFilename = path.join(tempDir, 'flute.opt.wasm');
+    final wasmFile = File(wasmFilename);
+    final optWasmFile = File(wasmFilename);
+
+    // Ensure we can print unoptimized dart2wasm modules
+    await run([
+      Platform.executable,
+      'compile',
+      'wasm',
+      '-O0',
+      dartFilename,
+      '-o',
+      wasmFilename,
+    ]);
+    wasmPrint(wasmFile.readAsBytesSync());
+
+    // Ensure we can print wasm-opt optimized wasm modules
+    await run([
+      Platform.executable,
+      'compile',
+      'wasm',
+      '-O3',
+      dartFilename,
+      '-o',
+      optWasmFilename,
+    ]);
+    wasmPrint(optWasmFile.readAsBytesSync());
+
+    // Temporary files will be deleted when returning to [withTempDir].
+  });
+}
+
+void wasmPrint(Uint8List wasmBytes) {
+  final deserializer = Deserializer(wasmBytes);
+  final module = Module.deserialize(deserializer);
+  print('len = ${module.printAsWat().length}');
+}

pkg/wasm_builder/lib/src/ir/function.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../serialize/serialize.dart';
+import '../serialize/printer.dart';
 import 'ir.dart';
 
 /// A local variable defined in a function.
@@ -12,6 +13,15 @@ class Local {
 
   Local(this.index, this.type);
 
+  void printTo(IrPrinter p, Map<int, String> localNames,
+      {bool isParam = false}) {
+    p.write(isParam ? 'param' : 'local');
+    p.write(' ');
+    p.writeLocalIndexReference(index);
+    p.write(' ');
+    p.writeValueType(type);
+  }
+
   @override
   String toString() => "$index";
 }
@@ -82,6 +92,39 @@ class DefinedFunction extends BaseFunction implements Serializable {
     s.writeData(localS);
   }
 
+  void printTo(IrPrinter p) {
+    p.write('(func ');
+    p.writeFunctionReference(this);
+    String? exportName;
+    for (final f in enclosingModule.exports.exported) {
+      if (f is FunctionExport && f.function == this) {
+        exportName = f.name;
+        break;
+      }
+    }
+    if (exportName != null) {
+      p.write(' ');
+      p.writeExport(exportName);
+    }
+
+    p.withLocalNames(localNames, () {
+      if (type.inputs.isNotEmpty || type.outputs.isNotEmpty) {
+        p.write(' ');
+        type.printSignatureWithNamesTo(p, oneLine: true);
+      }
+      p.writeln('');
+      p.withIndent(() {
+        for (int i = type.inputs.length; i < locals.length; ++i) {
+          p.write('(');
+          locals[i].printTo(p, localNames);
+          p.writeln(')');
+        }
+        body.printTo(p);
+      });
+    });
+    p.write(')');
+  }
+
   @override
   String toString() => functionName ?? "#$finalizableIndex";
 }
@@ -105,6 +148,15 @@ class ImportedFunction extends BaseFunction implements Import {
     s.writeUnsigned(type.index);
   }
 
+  void printTo(IrPrinter p) {
+    p.write('(func ');
+    p.writeFunctionReference(this);
+    p.writeImport(module, name);
+    p.write(' ');
+    type.printOneLineSignatureTo(p);
+    p.write(')');
+  }
+
   @override
   String toString() => "$module.$name";
 }

pkg/wasm_builder/lib/src/ir/global.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../serialize/serialize.dart';
+import '../serialize/printer.dart';
 import 'ir.dart';
 
 /// An (imported or defined) global variable.
@@ -26,6 +27,8 @@ abstract class Global with Indexable, Exportable {
   Export buildExport(String name) {
     return GlobalExport(name, this);
   }
+
+  void printTo(IrPrinter p) => throw 'not implemented';
 }
 
 /// A global variable defined in a module.
@@ -41,6 +44,21 @@ class DefinedGlobal extends Global implements Serializable {
     s.write(type);
     s.write(initializer);
   }
+
+  @override
+  void printTo(IrPrinter p) {
+    // This may generate globals this one refers to.
+    final ip = p.dup();
+    initializer.printInitializerTo(ip);
+
+    p.write('(global ');
+    p.writeGlobalReference(this);
+    p.write(' ');
+    type.printTo(p);
+    p.write(' ');
+    p.write(ip.getText().trim());
+    p.write(')');
+  }
 }
 
 /// An imported global variable.
@@ -62,6 +80,17 @@ class ImportedGlobal extends Global implements Import {
     s.writeByte(0x03);
     s.write(type);
   }
+
+  @override
+  void printTo(IrPrinter p) {
+    p.write('(global ');
+    p.writeGlobalReference(this);
+    p.write(' ');
+    p.writeImport(module, name);
+    p.write(' ');
+    p.writeValueType(type.type);
+    p.write(')');
+  }
 }
 
 class GlobalExport extends Export {