pkg/vm/lib/transformations/ffi_definitions.dart - sdk.git - Git at Google

 // Copyright (c) 2019, 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.

 library vm.transformations.ffi_definitions;

 import 'dart:math' as math;

 import 'package:front_end/src/api_unstable/vm.dart'
     show
         templateFfiFieldAnnotation,
         templateFfiFieldNoAnnotation,
         templateFfiTypeMismatch,
         templateFfiFieldInitializer,
         templateFfiStructGeneric;

 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 import 'package:kernel/core_types.dart';
 import 'package:kernel/library_index.dart' show LibraryIndex;
 import 'package:kernel/target/targets.dart' show DiagnosticReporter;
 import 'package:kernel/type_environment.dart' show SubtypeCheckMode;

 import 'ffi.dart';

 /// Checks and elaborates the dart:ffi structs and fields.
 ///
 /// Input:
 /// class Coord extends Struct {
 ///   @Double()
 ///   double x;
 ///
 ///   @Double()
 ///   double y;
 ///
 ///   Coord next;
 /// }
 ///
 /// Output:
 /// class Coord extends Struct {
 ///   Coord.#fromPointer(Pointer<Coord> coord) : super._(coord);
 ///
 ///   Pointer<Double> get _xPtr => addressOf.cast();
 ///   set x(double v) => _xPtr.store(v);
 ///   double get x => _xPtr.load();
 ///
 ///   Pointer<Double> get _yPtr => addressOf.offsetBy(...).cast();
 ///   set y(double v) => _yPtr.store(v);
 ///   double get y => _yPtr.load();
 ///
 ///   ffi.Pointer<Coordinate> get _nextPtr => addressof.offsetBy(...).cast();
 ///   set next(Coordinate v) => _nextPtr.store(v);
 ///   Coordinate get next => _nextPtr.load();
 ///
 ///   static final int #sizeOf = 24;
 /// }
 ReplacedMembers transformLibraries(
     Component component,
     CoreTypes coreTypes,
     ClassHierarchy hierarchy,
     List<Library> libraries,
     DiagnosticReporter diagnosticReporter) {
   final LibraryIndex index =
       LibraryIndex(component, const ["dart:ffi", "dart:core"]);
   if (!index.containsLibrary("dart:ffi")) {
     // If dart:ffi is not loaded, do not do the transformation.
     return ReplacedMembers({}, {});
   }
   final transformer = new _FfiDefinitionTransformer(
       index, coreTypes, hierarchy, diagnosticReporter);
   libraries.forEach(transformer.visitLibrary);
   return ReplacedMembers(
       transformer.replacedGetters, transformer.replacedSetters);
 }

 /// Checks and elaborates the dart:ffi structs and fields.
 class _FfiDefinitionTransformer extends FfiTransformer {
   final LibraryIndex index;

   Map<Field, Procedure> replacedGetters = {};
   Map<Field, Procedure> replacedSetters = {};

   _FfiDefinitionTransformer(this.index, CoreTypes coreTypes,
       ClassHierarchy hierarchy, DiagnosticReporter diagnosticReporter)
       : super(index, coreTypes, hierarchy, diagnosticReporter) {}

   @override
   visitExtension(Extension node) {
     // The extension and it's members are only metadata.
     return node;
   }

   @override
   visitClass(Class node) {
     if (!hierarchy.isSubclassOf(node, structClass) || node == structClass) {
       return node;
     }

     _checkStructClass(node);

     // Struct objects are manufactured in the VM by 'allocate' and 'load'.
     _makeEntryPoint(node);

     _checkConstructors(node);
     final bool fieldsValid = _checkFieldAnnotations(node);

     if (fieldsValid) {
       final structSize = _replaceFields(node);
       _replaceSizeOfMethod(node, structSize);
     }

     return node;
   }

   void _checkStructClass(Class node) {
     if (node.typeParameters.length > 0) {
       diagnosticReporter.report(
           templateFfiStructGeneric.withArguments(node.name),
           node.fileOffset,
           1,
           node.location.file);
     }

     if (node.supertype?.classNode != structClass) {
       // Not a struct, but extends a struct. The error will be emitted by
       // _FfiUseSiteTransformer.
       return;
     }
   }

   bool _isPointerType(Field field) {
     return env.isSubtypeOf(
         field.type,
         InterfaceType(pointerClass,
             [InterfaceType(nativeTypesClasses[NativeType.kNativeType.index])]),
         SubtypeCheckMode.ignoringNullabilities);
   }

   bool _checkFieldAnnotations(Class node) {
     bool success = true;
     for (final Field f in node.fields) {
       if (f.initializer is! NullLiteral) {
         diagnosticReporter.report(
             templateFfiFieldInitializer.withArguments(f.name.name),
             f.fileOffset,
             f.name.name.length,
             f.fileUri);
       }
       final nativeTypeAnnos = _getNativeTypeAnnotations(f).toList();
       if (_isPointerType(f)) {
         if (nativeTypeAnnos.length != 0) {
           diagnosticReporter.report(
               templateFfiFieldNoAnnotation.withArguments(f.name.name),
               f.fileOffset,
               f.name.name.length,
               f.fileUri);
         }
       } else if (nativeTypeAnnos.length != 1) {
         diagnosticReporter.report(
             templateFfiFieldAnnotation.withArguments(f.name.name),
             f.fileOffset,
             f.name.name.length,
             f.fileUri);
       } else {
         final DartType dartType = f.type;
         final DartType nativeType =
             InterfaceType(nativeTypesClasses[nativeTypeAnnos.first.index]);
         // TODO(36730): Support structs inside structs.
         final DartType shouldBeDartType =
             convertNativeTypeToDartType(nativeType, /*allowStructs=*/ false);
         if (shouldBeDartType == null ||
             !env.isSubtypeOf(dartType, shouldBeDartType,
                 SubtypeCheckMode.ignoringNullabilities)) {
           diagnosticReporter.report(
               templateFfiTypeMismatch.withArguments(
                   dartType, shouldBeDartType, nativeType),
               f.fileOffset,
               1,
               f.location.file);
           success = false;
         }
       }
     }
     return success;
   }

   void _checkConstructors(Class node) {
     final toRemove = <Initializer>[];

     // Constructors cannot have initializers because initializers refer to
     // fields, and the fields were replaced with getter/setter pairs.
     for (final Constructor c in node.constructors) {
       for (final Initializer i in c.initializers) {
         if (i is FieldInitializer) {
           toRemove.add(i);
           diagnosticReporter.report(
               templateFfiFieldInitializer.withArguments(i.field.name.name),
               i.fileOffset,
               1,
               i.location.file);
         }
       }
     }
     // Remove initializers referring to fields to prevent cascading errors.
     for (final Initializer i in toRemove) {
       i.remove();
     }

     // Add a constructor which 'load' can use.
     // C.#fromPointer(Pointer<Void> address) : super.fromPointer(address);
     final VariableDeclaration pointer = new VariableDeclaration("#pointer");
     final Constructor ctor = Constructor(
         FunctionNode(EmptyStatement(), positionalParameters: [pointer]),
         name: Name("#fromPointer"),
         initializers: [
           SuperInitializer(structFromPointer, Arguments([VariableGet(pointer)]))
         ]);
     _makeEntryPoint(ctor);
     node.addMember(ctor);
   }

   /// Computes the field offsets (for all ABIs) in the struct and replaces the
   /// fields with getters and setters using these offsets.
   ///
   /// Returns the total size of the struct (for all ABIs).
   Map<Abi, int> _replaceFields(Class node) {
     final fields = <Field>[];
     final types = <NativeType>[];

     for (final Field f in node.fields) {
       if (_isPointerType(f)) {
         fields.add(f);
         types.add(NativeType.kPointer);
       } else {
         final nativeTypeAnnos = _getNativeTypeAnnotations(f).toList();
         if (nativeTypeAnnos.length == 1) {
           final NativeType t = nativeTypeAnnos.first;
           fields.add(f);
           types.add(t);
         }
       }
     }

     final sizeAndOffsets = <Abi, SizeAndOffsets>{};
     for (final Abi abi in Abi.values) {
       sizeAndOffsets[abi] = _calculateSizeAndOffsets(types, abi);
     }

     for (int i = 0; i < fields.length; i++) {
       final fieldOffsets = sizeAndOffsets
           .map((Abi abi, SizeAndOffsets v) => MapEntry(abi, v.offsets[i]));
       final methods =
           _generateMethodsForField(fields[i], types[i], fieldOffsets);
       methods.forEach((p) => node.addMember(p));
     }

     for (final Field f in fields) {
       f.remove();
     }

     return sizeAndOffsets.map((k, v) => MapEntry(k, v.size));
   }

   /// Expression that queries VM internals at runtime to figure out on which ABI
   /// we are.
   Expression _runtimeBranchOnLayout(Map<Abi, int> values) {
     return MethodInvocation(
         ConstantExpression(
             ListConstant(InterfaceType(intClass), [
               IntConstant(values[Abi.wordSize64]),
               IntConstant(values[Abi.wordSize32Align32]),
               IntConstant(values[Abi.wordSize32Align64])
             ]),
             InterfaceType(intClass)),
         Name("[]"),
         Arguments([StaticInvocation(abiMethod, Arguments([]))]),
         listElementAt);
   }

   /// Sample output:
   /// ffi.Pointer<ffi.Double> get _xPtr => addressOf.cast();
   /// double get x => _xPtr.load();
   /// set x(double v) => _xPtr.store(v);
   List<Procedure> _generateMethodsForField(
       Field field, NativeType type, Map<Abi, int> offsets) {
     final DartType nativeType = type == NativeType.kPointer
         ? field.type
         : InterfaceType(nativeTypesClasses[type.index]);
     final DartType pointerType = InterfaceType(pointerClass, [nativeType]);
     final Name pointerName = Name('#_ptr_${field.name.name}');

     // Sample output:
     // ffi.Pointer<ffi.Double> get _xPtr => addressOf.offsetBy(...).cast<ffi.Pointer<ffi.Double>>();
     Expression pointer =
         PropertyGet(ThisExpression(), addressOfField.name, addressOfField);
     final hasNonZero = offsets.values.skipWhile((i) => i == 0).isNotEmpty;
     if (hasNonZero) {
       pointer = MethodInvocation(pointer, offsetByMethod.name,
           Arguments([_runtimeBranchOnLayout(offsets)]), offsetByMethod);
     }

     final Class nativeClass = (nativeType as InterfaceType).classNode;
     final NativeType nt = getType(nativeClass);
     final typeArguments = [
       if (nt == NativeType.kPointer && pointerType is InterfaceType)
         pointerType.typeArguments[0]
     ];

     final Procedure pointerGetter = Procedure(
         pointerName,
         ProcedureKind.Getter,
         FunctionNode(
             ReturnStatement(MethodInvocation(pointer, castMethod.name,
                 Arguments([], types: [nativeType]), castMethod)),
             returnType: pointerType),
         fileUri: field.fileUri)
       ..fileOffset = field.fileOffset;

     // Sample output:
     // double get x => _xPtr.value;
     final loadMethod =
         optimizedTypes.contains(nt) ? loadMethods[nt] : loadStructMethod;
     final Procedure getter = Procedure(
         field.name,
         ProcedureKind.Getter,
         FunctionNode(
             ReturnStatement(StaticInvocation(
                 loadMethod,
                 Arguments([
                   PropertyGet(ThisExpression(), pointerName, pointerGetter),
                   ConstantExpression(IntConstant(0))
                 ], types: typeArguments))),
             returnType: field.type),
         fileUri: field.fileUri)
       ..fileOffset = field.fileOffset;

     // Sample output:
     // set x(double v) { _xPtr.value = v; };
     final storeMethod = storeMethods[nt];
     Procedure setter = null;
     if (!field.isFinal) {
       final VariableDeclaration argument =
           VariableDeclaration('#v', type: field.type);
       setter = Procedure(
           field.name,
           ProcedureKind.Setter,
           FunctionNode(
               ReturnStatement(StaticInvocation(
                   storeMethod,
                   Arguments([
                     PropertyGet(ThisExpression(), pointerName, pointerGetter),
                     ConstantExpression(IntConstant(0)),
                     VariableGet(argument)
                   ], types: typeArguments))),
               returnType: VoidType(),
               positionalParameters: [argument]),
           fileUri: field.fileUri)
         ..fileOffset = field.fileOffset;
     }

     replacedGetters[field] = getter;
     replacedSetters[field] = setter;

     return [pointerGetter, getter, if (setter != null) setter];
   }

   /// Sample output:
   /// static int #sizeOf() => 24;
   void _replaceSizeOfMethod(Class struct, Map<Abi, int> sizes) {
     final Field sizeOf = Field(Name("#sizeOf"),
         isStatic: true,
         isFinal: true,
         initializer: _runtimeBranchOnLayout(sizes),
         type: InterfaceType(intClass));
     _makeEntryPoint(sizeOf);
     struct.addMember(sizeOf);
   }

   int _sizeInBytes(NativeType type, Abi abi) {
     final int size = nativeTypeSizes[type.index];
     if (size == WORD_SIZE) {
       return wordSize[abi];
     }
     return size;
   }

   int _alignmentOf(NativeType type, Abi abi) {
     final int alignment = nonSizeAlignment[abi][type];
     if (alignment != null) return alignment;
     return _sizeInBytes(type, abi);
   }

   int _alignOffset(int offset, int alignment) {
     final int remainder = offset % alignment;
     if (remainder != 0) {
       offset -= remainder;
       offset += alignment;
     }
     return offset;
   }

   // TODO(37271): Support nested structs.
   SizeAndOffsets _calculateSizeAndOffsets(List<NativeType> types, Abi abi) {
     int offset = 0;
     final offsets = <int>[];
     for (final NativeType t in types) {
       final int size = _sizeInBytes(t, abi);
       final int alignment = _alignmentOf(t, abi);
       offset = _alignOffset(offset, alignment);
       offsets.add(offset);
       offset += size;
     }
     final int minimumAlignment = 1;
     final sizeAlignment = types
         .map((t) => _alignmentOf(t, abi))
         .followedBy([minimumAlignment]).reduce(math.max);
     final int size = _alignOffset(offset, sizeAlignment);
     return SizeAndOffsets(size, offsets);
   }

   void _makeEntryPoint(Annotatable node) {
     node.addAnnotation(ConstantExpression(
         InstanceConstant(pragmaClass.reference, [], {
           pragmaName.reference: StringConstant("vm:entry-point"),
           pragmaOptions.reference: NullConstant()
         }),
         InterfaceType(pragmaClass, [])));
   }

   NativeType _getFieldType(Class c) {
     final fieldType = getType(c);

     if (fieldType == NativeType.kVoid) {
       // Fields cannot have Void types.
       return null;
     }
     return fieldType;
   }

   Iterable<NativeType> _getNativeTypeAnnotations(Field node) {
     return node.annotations
         .whereType<ConstantExpression>()
         .map((expr) => expr.constant)
         .whereType<InstanceConstant>()
         .map((constant) => constant.classNode)
         .map((klass) => _getFieldType(klass))
         .where((type) => type != null);
   }
 }

 class SizeAndOffsets {
   /// Size of the entire struct.
   final int size;

   /// Offset in bytes for each field, indexed by field number.
   final List<int> offsets;

   SizeAndOffsets(this.size, this.offsets);
 }
	// Copyright (c) 2019, 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.

	library vm.transformations.ffi_definitions;

	import 'dart:math' as math;

	import 'package:front_end/src/api_unstable/vm.dart'
	show
	templateFfiFieldAnnotation,
	templateFfiFieldNoAnnotation,
	templateFfiTypeMismatch,
	templateFfiFieldInitializer,
	templateFfiStructGeneric;

	import 'package:kernel/ast.dart' hide MapEntry;
	import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
	import 'package:kernel/core_types.dart';
	import 'package:kernel/library_index.dart' show LibraryIndex;
	import 'package:kernel/target/targets.dart' show DiagnosticReporter;
	import 'package:kernel/type_environment.dart' show SubtypeCheckMode;

	import 'ffi.dart';

	/// Checks and elaborates the dart:ffi structs and fields.
	///
	/// Input:
	/// class Coord extends Struct {
	/// @Double()
	/// double x;
	///
	/// @Double()
	/// double y;
	///
	/// Coord next;
	/// }
	///
	/// Output:
	/// class Coord extends Struct {
	/// Coord.#fromPointer(Pointer<Coord> coord) : super._(coord);
	///
	/// Pointer<Double> get _xPtr => addressOf.cast();
	/// set x(double v) => _xPtr.store(v);
	/// double get x => _xPtr.load();
	///
	/// Pointer<Double> get _yPtr => addressOf.offsetBy(...).cast();
	/// set y(double v) => _yPtr.store(v);
	/// double get y => _yPtr.load();
	///
	/// ffi.Pointer<Coordinate> get _nextPtr => addressof.offsetBy(...).cast();
	/// set next(Coordinate v) => _nextPtr.store(v);
	/// Coordinate get next => _nextPtr.load();
	///
	/// static final int #sizeOf = 24;
	/// }
	ReplacedMembers transformLibraries(
	Component component,
	CoreTypes coreTypes,
	ClassHierarchy hierarchy,
	List<Library> libraries,
	DiagnosticReporter diagnosticReporter) {
	final LibraryIndex index =
	LibraryIndex(component, const ["dart:ffi", "dart:core"]);
	if (!index.containsLibrary("dart:ffi")) {
	// If dart:ffi is not loaded, do not do the transformation.
	return ReplacedMembers({}, {});
	}
	final transformer = new _FfiDefinitionTransformer(
	index, coreTypes, hierarchy, diagnosticReporter);
	libraries.forEach(transformer.visitLibrary);
	return ReplacedMembers(
	transformer.replacedGetters, transformer.replacedSetters);
	}

	/// Checks and elaborates the dart:ffi structs and fields.
	class _FfiDefinitionTransformer extends FfiTransformer {
	final LibraryIndex index;

	Map<Field, Procedure> replacedGetters = {};
	Map<Field, Procedure> replacedSetters = {};

	_FfiDefinitionTransformer(this.index, CoreTypes coreTypes,
	ClassHierarchy hierarchy, DiagnosticReporter diagnosticReporter)
	: super(index, coreTypes, hierarchy, diagnosticReporter) {}

	@override
	visitExtension(Extension node) {
	// The extension and it's members are only metadata.
	return node;
	}

	@override
	visitClass(Class node) {
	if (!hierarchy.isSubclassOf(node, structClass) \|\| node == structClass) {
	return node;
	}

	_checkStructClass(node);

	// Struct objects are manufactured in the VM by 'allocate' and 'load'.
	_makeEntryPoint(node);

	_checkConstructors(node);
	final bool fieldsValid = _checkFieldAnnotations(node);

	if (fieldsValid) {
	final structSize = _replaceFields(node);
	_replaceSizeOfMethod(node, structSize);
	}

	return node;
	}

	void _checkStructClass(Class node) {
	if (node.typeParameters.length > 0) {
	diagnosticReporter.report(
	templateFfiStructGeneric.withArguments(node.name),
	node.fileOffset,
	1,
	node.location.file);
	}

	if (node.supertype?.classNode != structClass) {
	// Not a struct, but extends a struct. The error will be emitted by
	// _FfiUseSiteTransformer.
	return;
	}
	}

	bool _isPointerType(Field field) {
	return env.isSubtypeOf(
	field.type,
	InterfaceType(pointerClass,
	[InterfaceType(nativeTypesClasses[NativeType.kNativeType.index])]),
	SubtypeCheckMode.ignoringNullabilities);
	}

	bool _checkFieldAnnotations(Class node) {
	bool success = true;
	for (final Field f in node.fields) {
	if (f.initializer is! NullLiteral) {
	diagnosticReporter.report(
	templateFfiFieldInitializer.withArguments(f.name.name),
	f.fileOffset,
	f.name.name.length,
	f.fileUri);
	}
	final nativeTypeAnnos = _getNativeTypeAnnotations(f).toList();
	if (_isPointerType(f)) {
	if (nativeTypeAnnos.length != 0) {
	diagnosticReporter.report(
	templateFfiFieldNoAnnotation.withArguments(f.name.name),
	f.fileOffset,
	f.name.name.length,
	f.fileUri);
	}
	} else if (nativeTypeAnnos.length != 1) {
	diagnosticReporter.report(
	templateFfiFieldAnnotation.withArguments(f.name.name),
	f.fileOffset,
	f.name.name.length,
	f.fileUri);
	} else {
	final DartType dartType = f.type;
	final DartType nativeType =
	InterfaceType(nativeTypesClasses[nativeTypeAnnos.first.index]);
	// TODO(36730): Support structs inside structs.
	final DartType shouldBeDartType =
	convertNativeTypeToDartType(nativeType, /allowStructs=/ false);
	if (shouldBeDartType == null \|\|
	!env.isSubtypeOf(dartType, shouldBeDartType,
	SubtypeCheckMode.ignoringNullabilities)) {
	diagnosticReporter.report(
	templateFfiTypeMismatch.withArguments(
	dartType, shouldBeDartType, nativeType),
	f.fileOffset,
	1,
	f.location.file);
	success = false;
	}
	}
	}
	return success;
	}

	void _checkConstructors(Class node) {
	final toRemove = <Initializer>[];

	// Constructors cannot have initializers because initializers refer to
	// fields, and the fields were replaced with getter/setter pairs.
	for (final Constructor c in node.constructors) {
	for (final Initializer i in c.initializers) {
	if (i is FieldInitializer) {
	toRemove.add(i);
	diagnosticReporter.report(
	templateFfiFieldInitializer.withArguments(i.field.name.name),
	i.fileOffset,
	1,
	i.location.file);
	}
	}
	}
	// Remove initializers referring to fields to prevent cascading errors.
	for (final Initializer i in toRemove) {
	i.remove();
	}

	// Add a constructor which 'load' can use.
	// C.#fromPointer(Pointer<Void> address) : super.fromPointer(address);
	final VariableDeclaration pointer = new VariableDeclaration("#pointer");
	final Constructor ctor = Constructor(
	FunctionNode(EmptyStatement(), positionalParameters: [pointer]),
	name: Name("#fromPointer"),
	initializers: [
	SuperInitializer(structFromPointer, Arguments([VariableGet(pointer)]))
	]);
	_makeEntryPoint(ctor);
	node.addMember(ctor);
	}

	/// Computes the field offsets (for all ABIs) in the struct and replaces the
	/// fields with getters and setters using these offsets.
	///
	/// Returns the total size of the struct (for all ABIs).
	Map<Abi, int> _replaceFields(Class node) {
	final fields = <Field>[];
	final types = <NativeType>[];

	for (final Field f in node.fields) {
	if (_isPointerType(f)) {
	fields.add(f);
	types.add(NativeType.kPointer);
	} else {
	final nativeTypeAnnos = _getNativeTypeAnnotations(f).toList();
	if (nativeTypeAnnos.length == 1) {
	final NativeType t = nativeTypeAnnos.first;
	fields.add(f);
	types.add(t);
	}
	}
	}

	final sizeAndOffsets = <Abi, SizeAndOffsets>{};
	for (final Abi abi in Abi.values) {
	sizeAndOffsets[abi] = _calculateSizeAndOffsets(types, abi);
	}

	for (int i = 0; i < fields.length; i++) {
	final fieldOffsets = sizeAndOffsets
	.map((Abi abi, SizeAndOffsets v) => MapEntry(abi, v.offsets[i]));
	final methods =
	_generateMethodsForField(fields[i], types[i], fieldOffsets);
	methods.forEach((p) => node.addMember(p));
	}

	for (final Field f in fields) {
	f.remove();
	}

	return sizeAndOffsets.map((k, v) => MapEntry(k, v.size));
	}

	/// Expression that queries VM internals at runtime to figure out on which ABI
	/// we are.
	Expression _runtimeBranchOnLayout(Map<Abi, int> values) {
	return MethodInvocation(
	ConstantExpression(
	ListConstant(InterfaceType(intClass), [
	IntConstant(values[Abi.wordSize64]),
	IntConstant(values[Abi.wordSize32Align32]),
	IntConstant(values[Abi.wordSize32Align64])
	]),
	InterfaceType(intClass)),
	Name("[]"),
	Arguments([StaticInvocation(abiMethod, Arguments([]))]),
	listElementAt);
	}

	/// Sample output:
	/// ffi.Pointer<ffi.Double> get _xPtr => addressOf.cast();
	/// double get x => _xPtr.load();
	/// set x(double v) => _xPtr.store(v);
	List<Procedure> _generateMethodsForField(
	Field field, NativeType type, Map<Abi, int> offsets) {
	final DartType nativeType = type == NativeType.kPointer
	? field.type
	: InterfaceType(nativeTypesClasses[type.index]);
	final DartType pointerType = InterfaceType(pointerClass, [nativeType]);
	final Name pointerName = Name('#_ptr_${field.name.name}');

	// Sample output:
	// ffi.Pointer<ffi.Double> get _xPtr => addressOf.offsetBy(...).cast<ffi.Pointer<ffi.Double>>();
	Expression pointer =
	PropertyGet(ThisExpression(), addressOfField.name, addressOfField);
	final hasNonZero = offsets.values.skipWhile((i) => i == 0).isNotEmpty;
	if (hasNonZero) {
	pointer = MethodInvocation(pointer, offsetByMethod.name,
	Arguments([_runtimeBranchOnLayout(offsets)]), offsetByMethod);
	}

	final Class nativeClass = (nativeType as InterfaceType).classNode;
	final NativeType nt = getType(nativeClass);
	final typeArguments = [
	if (nt == NativeType.kPointer && pointerType is InterfaceType)
	pointerType.typeArguments[0]
	];

	final Procedure pointerGetter = Procedure(
	pointerName,
	ProcedureKind.Getter,
	FunctionNode(
	ReturnStatement(MethodInvocation(pointer, castMethod.name,
	Arguments([], types: [nativeType]), castMethod)),
	returnType: pointerType),
	fileUri: field.fileUri)
	..fileOffset = field.fileOffset;

	// Sample output:
	// double get x => _xPtr.value;
	final loadMethod =
	optimizedTypes.contains(nt) ? loadMethods[nt] : loadStructMethod;
	final Procedure getter = Procedure(
	field.name,
	ProcedureKind.Getter,
	FunctionNode(
	ReturnStatement(StaticInvocation(
	loadMethod,
	Arguments([
	PropertyGet(ThisExpression(), pointerName, pointerGetter),
	ConstantExpression(IntConstant(0))
	], types: typeArguments))),
	returnType: field.type),
	fileUri: field.fileUri)
	..fileOffset = field.fileOffset;

	// Sample output:
	// set x(double v) { _xPtr.value = v; };
	final storeMethod = storeMethods[nt];
	Procedure setter = null;
	if (!field.isFinal) {
	final VariableDeclaration argument =
	VariableDeclaration('#v', type: field.type);
	setter = Procedure(
	field.name,
	ProcedureKind.Setter,
	FunctionNode(
	ReturnStatement(StaticInvocation(
	storeMethod,
	Arguments([
	PropertyGet(ThisExpression(), pointerName, pointerGetter),
	ConstantExpression(IntConstant(0)),
	VariableGet(argument)
	], types: typeArguments))),
	returnType: VoidType(),
	positionalParameters: [argument]),
	fileUri: field.fileUri)
	..fileOffset = field.fileOffset;
	}

	replacedGetters[field] = getter;
	replacedSetters[field] = setter;

	return [pointerGetter, getter, if (setter != null) setter];
	}

	/// Sample output:
	/// static int #sizeOf() => 24;
	void _replaceSizeOfMethod(Class struct, Map<Abi, int> sizes) {
	final Field sizeOf = Field(Name("#sizeOf"),
	isStatic: true,
	isFinal: true,
	initializer: _runtimeBranchOnLayout(sizes),
	type: InterfaceType(intClass));
	_makeEntryPoint(sizeOf);
	struct.addMember(sizeOf);
	}

	int _sizeInBytes(NativeType type, Abi abi) {
	final int size = nativeTypeSizes[type.index];
	if (size == WORD_SIZE) {
	return wordSize[abi];
	}
	return size;
	}

	int _alignmentOf(NativeType type, Abi abi) {
	final int alignment = nonSizeAlignment[abi][type];
	if (alignment != null) return alignment;
	return _sizeInBytes(type, abi);
	}

	int _alignOffset(int offset, int alignment) {
	final int remainder = offset % alignment;
	if (remainder != 0) {
	offset -= remainder;
	offset += alignment;
	}
	return offset;
	}

	// TODO(37271): Support nested structs.
	SizeAndOffsets _calculateSizeAndOffsets(List<NativeType> types, Abi abi) {
	int offset = 0;
	final offsets = <int>[];
	for (final NativeType t in types) {
	final int size = _sizeInBytes(t, abi);
	final int alignment = _alignmentOf(t, abi);
	offset = _alignOffset(offset, alignment);
	offsets.add(offset);
	offset += size;
	}
	final int minimumAlignment = 1;
	final sizeAlignment = types
	.map((t) => _alignmentOf(t, abi))
	.followedBy([minimumAlignment]).reduce(math.max);
	final int size = _alignOffset(offset, sizeAlignment);
	return SizeAndOffsets(size, offsets);
	}

	void _makeEntryPoint(Annotatable node) {
	node.addAnnotation(ConstantExpression(
	InstanceConstant(pragmaClass.reference, [], {
	pragmaName.reference: StringConstant("vm:entry-point"),
	pragmaOptions.reference: NullConstant()
	}),
	InterfaceType(pragmaClass, [])));
	}

	NativeType _getFieldType(Class c) {
	final fieldType = getType(c);

	if (fieldType == NativeType.kVoid) {
	// Fields cannot have Void types.
	return null;
	}
	return fieldType;
	}

	Iterable<NativeType> _getNativeTypeAnnotations(Field node) {
	return node.annotations
	.whereType<ConstantExpression>()
	.map((expr) => expr.constant)
	.whereType<InstanceConstant>()
	.map((constant) => constant.classNode)
	.map((klass) => _getFieldType(klass))
	.where((type) => type != null);
	}
	}

	class SizeAndOffsets {
	/// Size of the entire struct.
	final int size;

	/// Offset in bytes for each field, indexed by field number.
	final List<int> offsets;

	SizeAndOffsets(this.size, this.offsets);
	}