[native_toolchain_c] Compile with -Os by default (#1744)

Closes: #1267

Author: dcharkes

pkgs/native_toolchain_c/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - For Android, produce dylibs with page-size set to 16kb by default.
   https://github.com/dart-lang/native/issues/1611
+- Make optimization level configurable. Defaults to `-Os` and `/Os`.
+  https://github.com/dart-lang/native/issues/1267
 
 ## 0.6.0
 

pkgs/native_toolchain_c/lib/native_toolchain_c.dart

@@ -9,5 +9,6 @@ export 'src/cbuilder/cbuilder.dart' show CBuilder;
 export 'src/cbuilder/clinker.dart' show CLinker;
 export 'src/cbuilder/language.dart' show Language;
 export 'src/cbuilder/linker_options.dart' show LinkerOptions;
+export 'src/cbuilder/optimization_level.dart';
 export 'src/cbuilder/output_type.dart' show OutputType;
 export 'src/utils/env_from_bat.dart';

pkgs/native_toolchain_c/lib/src/cbuilder/cbuilder.dart

@@ -11,6 +11,7 @@ import 'package:native_assets_cli/code_assets_builder.dart';
 import 'ctool.dart';
 import 'language.dart';
 import 'linkmode.dart';
+import 'optimization_level.dart';
 import 'output_type.dart';
 import 'run_cbuilder.dart';
 
@@ -67,6 +68,7 @@ class CBuilder extends CTool implements Builder {
     super.language = Language.c,
     super.cppLinkStdLib,
     super.linkModePreference,
+    super.optimizationLevel = OptimizationLevel.oS,
   }) : super(type: OutputType.library);
 
   CBuilder.executable({
@@ -87,6 +89,7 @@ class CBuilder extends CTool implements Builder {
     super.std,
     super.language = Language.c,
     super.cppLinkStdLib,
+    super.optimizationLevel = OptimizationLevel.oS,
   }) : super(
           type: OutputType.executable,
           assetName: null,
@@ -158,6 +161,7 @@ class CBuilder extends CTool implements Builder {
         std: std,
         language: language,
         cppLinkStdLib: cppLinkStdLib,
+        optimizationLevel: optimizationLevel,
       );
       await task.run();
     }

pkgs/native_toolchain_c/lib/src/cbuilder/clinker.dart

@@ -12,6 +12,7 @@ import 'ctool.dart';
 import 'language.dart';
 import 'linker_options.dart';
 import 'linkmode.dart';
+import 'optimization_level.dart';
 import 'output_type.dart';
 import 'run_cbuilder.dart';
 
@@ -36,6 +37,7 @@ class CLinker extends CTool implements Linker {
     super.language = Language.c,
     super.cppLinkStdLib,
     super.linkModePreference,
+    super.optimizationLevel = OptimizationLevel.oS,
   }) : super(type: OutputType.library);
 
   /// Runs the C Linker with on this C build spec.
@@ -84,6 +86,7 @@ class CLinker extends CTool implements Linker {
       std: std,
       language: language,
       cppLinkStdLib: cppLinkStdLib,
+      optimizationLevel: optimizationLevel,
     );
     await task.run();
 

pkgs/native_toolchain_c/lib/src/cbuilder/ctool.dart

@@ -7,6 +7,7 @@ import 'package:native_assets_cli/code_assets.dart';
 
 import 'cbuilder.dart';
 import 'language.dart';
+import 'optimization_level.dart';
 import 'output_type.dart';
 
 abstract class CTool {
@@ -120,6 +121,9 @@ abstract class CTool {
   /// the value is instead retrieved from the [LinkConfig].
   final LinkModePreference? linkModePreference;
 
+  /// What optimization level should be used for compiling.
+  final OptimizationLevel optimizationLevel;
+
   CTool({
     required this.name,
     required this.assetName,
@@ -135,5 +139,6 @@ abstract class CTool {
     required this.cppLinkStdLib,
     required this.linkModePreference,
     required this.type,
+    required this.optimizationLevel,
   });
 }

pkgs/native_toolchain_c/lib/src/cbuilder/optimization_level.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2024, 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.
+
+/// Optimization level for code compilation.
+///
+/// For more information refer to compiler documentation:
+/// * https://clang.llvm.org/docs/CommandGuide/clang.html#code-generation-options
+/// * https://learn.microsoft.com/en-us/cpp/build/reference/o-options-optimize-code?view=msvc-170
+final class OptimizationLevel {
+  /// The optimization level.
+  final String _level;
+
+  const OptimizationLevel._(this._level);
+
+  /// No optimization; prioritize fast compilation.
+  static const OptimizationLevel o0 = OptimizationLevel._('O0');
+
+  /// Basic optimizations; balance compilation speed and code size.
+  static const OptimizationLevel o1 = OptimizationLevel._('O1');
+
+  /// More aggressive optimizations; prioritize code size reduction.
+  static const OptimizationLevel o2 = OptimizationLevel._('O2');
+
+  /// The most aggressive optimizations; prioritize runtime performance.
+  ///
+  /// Not supported in MSVC, defaults to [o2] for MSVC.
+  static const OptimizationLevel o3 = OptimizationLevel._('O3');
+
+  /// Optimize for code size, even if it impacts runtime performance.
+  static const OptimizationLevel oS = OptimizationLevel._('Os');
+
+  /// Unspecified optimization level; the default or compiler-chosen level.
+  static const OptimizationLevel unspecified =
+      OptimizationLevel._('unspecified');
+
+  /// Returns the string representation of the optimization level.
+  @override
+  String toString() => _level;
+
+  String clangFlag() => '-$_level';
+
+  String msvcFlag() => switch (this) {
+        o3 => o2.msvcFlag(),
+        _ => '/$_level',
+      };
+
+  static const List<OptimizationLevel> values = [
+    o0,
+    o1,
+    o2,
+    o3,
+    oS,
+    unspecified,
+  ];
+}

pkgs/native_toolchain_c/lib/src/cbuilder/run_cbuilder.dart

@@ -16,6 +16,7 @@ import '../utils/run_process.dart';
 import 'compiler_resolver.dart';
 import 'language.dart';
 import 'linker_options.dart';
+import 'optimization_level.dart';
 
 class RunCBuilder {
   /// The options are for linking only, so this will be non-null iff a linker
@@ -45,6 +46,7 @@ class RunCBuilder {
   final String? std;
   final Language language;
   final String? cppLinkStdLib;
+  final OptimizationLevel optimizationLevel;
 
   RunCBuilder({
     required this.config,
@@ -64,6 +66,7 @@ class RunCBuilder {
     this.std,
     this.language = Language.c,
     this.cppLinkStdLib,
+    required this.optimizationLevel,
   })  : outDir = config.outputDirectory,
         assert([executable, dynamicLibrary, staticLibrary]
                 .whereType<Uri>()
@@ -275,6 +278,8 @@ class RunCBuilder {
           '-l',
           cppLinkStdLib ?? defaultCppLinkStdLib[config.targetOS]!
         ],
+        if (optimizationLevel != OptimizationLevel.unspecified)
+          optimizationLevel.clangFlag(),
         ...linkerOptions?.preSourcesFlags(toolInstance.tool, sourceFiles) ?? [],
         // Support Android 15 page size by default, can be overridden by
         // passing [flags].
@@ -327,6 +332,8 @@ class RunCBuilder {
     final result = await runProcess(
       executable: tool.uri,
       arguments: [
+        if (optimizationLevel != OptimizationLevel.unspecified)
+          optimizationLevel.msvcFlag(),
         if (std != null) '/std:$std',
         if (language == Language.cpp) '/TP',
         ...flags,

pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_android_test.dart

@@ -36,21 +36,30 @@ void main() {
   /// From https://docs.flutter.dev/reference/supported-platforms.
   const flutterAndroidNdkVersionHighestSupported = 34;
 
+  const optimizationLevels = OptimizationLevel.values;
+  var selectOptimizationLevel = 0;
+
   for (final linkMode in [DynamicLoadingBundled(), StaticLinking()]) {
     for (final target in targets) {
       for (final apiLevel in [
         flutterAndroidNdkVersionLowestBestEffort,
         flutterAndroidNdkVersionLowestSupported,
         flutterAndroidNdkVersionHighestSupported,
       ]) {
-        test('CBuilder $linkMode library $target minSdkVersion $apiLevel',
-            () async {
+        // Cycle through all optimization levels.
+        final optimizationLevel = optimizationLevels[selectOptimizationLevel];
+        selectOptimizationLevel =
+            (selectOptimizationLevel + 1) % optimizationLevels.length;
+        test(
+            'CBuilder $linkMode library $target minSdkVersion $apiLevel '
+            '$optimizationLevel', () async {
           final tempUri = await tempDirForTest();
           final libUri = await buildLib(
             tempUri,
             target,
             apiLevel,
             linkMode,
+            optimizationLevel: optimizationLevel,
           );
           if (Platform.isLinux) {
             final machine = await readelfMachine(libUri.path);
@@ -128,6 +137,7 @@ Future<Uri> buildLib(
   int androidNdkApi,
   LinkMode linkMode, {
   List<String> flags = const [],
+  OptimizationLevel optimizationLevel = OptimizationLevel.o3,
 }) async {
   final addCUri = packageUri.resolve('test/cbuilder/testfiles/add/src/add.c');
   const name = 'add';

pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_ios_test.dart

@@ -35,23 +35,30 @@ void main() {
 
   const name = 'add';
 
+  const optimizationLevels = OptimizationLevel.values;
+  var selectOptimizationLevel = 0;
+
   for (final language in [Language.c, Language.objectiveC]) {
     for (final linkMode in [DynamicLoadingBundled(), StaticLinking()]) {
       for (final targetIOSSdk in IOSSdk.values) {
         for (final target in targets) {
           if (target == Architecture.x64 && targetIOSSdk == IOSSdk.iPhoneOS) {
             continue;
           }
-
           final libName = OS.iOS.libraryFileName(name, linkMode);
           for (final installName in [
             null,
             if (linkMode == DynamicLoadingBundled())
               Uri.file('@executable_path/Frameworks/$libName'),
           ]) {
+            // Cycle through all optimization levels.
+            final optimizationLevel =
+                optimizationLevels[selectOptimizationLevel];
+            selectOptimizationLevel =
+                (selectOptimizationLevel + 1) % optimizationLevels.length;
             test(
                 'CBuilder $linkMode $language library $targetIOSSdk $target'
-                        ' ${installName ?? ''}'
+                        ' ${installName ?? ''} $optimizationLevel'
                     .trim(), () async {
               final tempUri = await tempDirForTest();
               final tempUri2 = await tempDirForTest();
@@ -97,6 +104,7 @@ void main() {
                 sources: [sourceUri.toFilePath()],
                 installName: installName,
                 language: language,
+                optimizationLevel: optimizationLevel,
               );
               await cbuilder.run(
                 config: buildConfig,

pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_linux_host_test.dart

@@ -26,9 +26,16 @@ void main() {
     Architecture.riscv64,
   ];
 
+  const optimizationLevels = OptimizationLevel.values;
+  var selectOptimizationLevel = 0;
+
   for (final linkMode in [DynamicLoadingBundled(), StaticLinking()]) {
     for (final target in targets) {
-      test('CBuilder $linkMode library $target', () async {
+      // Cycle through all optimization levels.
+      final optimizationLevel = optimizationLevels[selectOptimizationLevel];
+      selectOptimizationLevel =
+          (selectOptimizationLevel + 1) % optimizationLevels.length;
+      test('CBuilder $linkMode library $target $optimizationLevel', () async {
         final tempUri = await tempDirForTest();
         final tempUri2 = await tempDirForTest();
         final addCUri =
@@ -66,6 +73,7 @@ void main() {
           name: name,
           assetName: name,
           sources: [addCUri.toFilePath()],
+          optimizationLevel: optimizationLevel,
         );
         await cbuilder.run(
           config: buildConfig,