pkg/dart2wasm/lib/prod/cfg/code_generator.dart

// Copyright (c) 2026, 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 'package:cfg/front_end/ast_to_ir.dart';
import 'package:cfg/front_end/computed_scopes.dart';
import 'package:cfg/ir/ssa_computation.dart';
import 'package:cfg/passes/constant_propagation.dart';
import 'package:cfg/passes/control_flow_optimizations.dart';
import 'package:cfg/passes/pass.dart';
import 'package:cfg/passes/simplification.dart';
import 'package:cfg/passes/value_numbering.dart';
import 'package:kernel/ast.dart';
import 'package:wasm_builder/wasm_builder.dart' as w;

import '../../cfg/passes/lower_irreducible_control_flow.dart';
import '../../code_generator.dart';
import '../../intrinsics.dart';
import '../../reference_extensions.dart';
import '../../translator.dart';
import '../../util.dart';
import 'to_wasm.dart';

bool mayUseCfgToCompileMember(Translator translator, Member member) {
  if (!translator.options.useCfg) return false;

  String? failureReason;
  if (member is Procedure) {
    if (member.function.asyncMarker != AsyncMarker.Sync) {
      failureReason = 'async';
    }
    if (StaticIntrinsic.fromProcedure(translator.coreTypes, member) != null ||
        MemberIntrinsic.fromProcedure(translator.coreTypes, member) != null) {
      failureReason = 'an intrinsic';
    }
    if (member.isExternal) failureReason = 'external';
  } else if (member is Field) {
    if (!member.isInstanceMember) failureReason = 'static';
  } else {
    failureReason = 'not a procedure or field';
  }

  final hasCfgPragma = hasWasmCfgPragma(translator.coreTypes, member);

  if (failureReason != null) {
    if (hasCfgPragma) {
      throw StateError(
        'Member $member has @pragma("wasm:cfg") but is $failureReason.',
      );
    }
    return false;
  }

  // Avoid compiling platform libraries (`dart:*`) with CFG as the CFG
  // pipeline is still under development and only supports a subset of
  // constructs, unless explicitly requested via `@pragma('wasm:cfg')`.
  if (member.enclosingLibrary.importUri.isScheme('dart') && !hasCfgPragma) {
    return false;
  }

  return true;
}

class CfgMemberCodeGenerator implements CodeGenerator {
  final AstCodeGenerator fallback;
  final Reference reference;

  CfgMemberCodeGenerator(this.fallback, this.reference);

  Translator get translator => fallback.translator;
  Member get member => fallback.enclosingMember;
  EntryPoint get kind => reference.entryKind;

  @override
  void generate(
    w.InstructionsBuilder b,
    List<w.Local> paramLocals,
    w.Label? returnLabel,
  ) {
    assert(returnLabel == null);
    assert(translator.options.useCfg);
    final allowFallback = !hasWasmCfgPragma(translator.coreTypes, member);

    if (allowFallback) {
      try {
        if (_tryGenerate(b, paramLocals)) return;
      } catch (_) {}
      translator.cfgLog?.appendFailed(member);
      b.reset();
      fallback.generate(b, paramLocals, returnLabel);
    } else {
      if (!_tryGenerate(b, paramLocals)) {
        throw StateError(
          'Member $member ($reference) has @pragma("wasm:cfg") but failed to compile with CFG.',
        );
      }
    }
  }

  bool _tryGenerate(w.InstructionsBuilder b, List<w.Local> paramLocals) {
    final cFunction = translator.functionRegistry.getFunction(
      member,
      isGetter: reference.isGetter,
      isSetter: reference.isSetter,
    );

    final graph = AstToIr(
      cFunction,
      translator.functionRegistry,
      translator.recognizedMethods,
      onLocalFunction: (_) {},
      enableAsserts: translator.options.enableAsserts,
      typeParametersStyle: .separateFunctionAndClassTypeParameters,
      scopes: ComputedScopes(
        member,
        enableAsserts: translator.options.enableAsserts,
      ),
    ).buildFlowGraph();

    final pipeline = Pipeline([
      SSAComputation(),
      ValueNumbering(simplification: Simplification()),
      ConstantPropagation(),
      LowerIrreducibleControlFlow(),
      ControlFlowOptimizations(),
    ]);

    pipeline.run(graph);

    final cfgToWasm = ProdCfgToWasm(
      translator,
      graph,
      b,
      paramLocals,
      kind: kind,
    );

    if (!cfgToWasm.canTranslate()) {
      return false;
    }

    cfgToWasm.generate();
    return true;
  }
}