110 строки
3.9 KiB
C#
110 строки
3.9 KiB
C#
using System;
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using System.Collections.Generic;
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using Mono.Linker;
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using Mono.Linker.Steps;
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using Xamarin.Tuner;
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#nullable enable
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namespace Xamarin.Linker {
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// Problems:
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// * `Dispose` set the generated backing fields to `null` which means
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// the linker will mark every backing fields, even if not used
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// elsewhere (generally properties) inside the class
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// * Backing fields increase the memory footprint of the managed peer
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// instance (for the type and all it's subclasses)
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// * Backing fields also increase the app size. Not a huge problem as
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// they are all declared _weakly_ as `NSObject` but still...
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//
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// Solution:
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// * When the linker process a `Dispose` method of an `NSObject`
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// subclass with the _optimizable_ attribute then we remove the
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// method body. This way the linker cannot mark the fields.
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// * Before saving back the assemblies we replace the cached method
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// body and NOP every field that were not marked by something else
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// than the `Dispose` method.
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public class BackingFieldDelayHandler : ConfigurationAwareMarkHandler {
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protected override string Name { get; } = "Backing Fields Optimizer";
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protected override int ErrorCode { get; } = 2400;
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public override void Initialize (LinkContext context, MarkContext markContext)
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{
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base.Initialize (context);
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markContext.RegisterMarkMethodAction (ProcessMethod);
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}
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// cache `Dispose` body of optimization NSObject subclasses
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static Dictionary<MethodDefinition, MethodBody> dispose = new ();
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protected override void Process (MethodDefinition method)
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{
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if (!method.HasParameters || !method.IsVirtual || !method.HasBody)
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return;
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if (method.Name != "Dispose")
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return;
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// only process methods that are marked as optimizable
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if (!method.IsBindingImplOptimizableCode (LinkContext))
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return;
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var t = method.DeclaringType;
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if (!t.IsNSObject (LinkContext))
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return;
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// keep original for later (if needed)
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dispose.Add (method, method.Body);
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// setting body to null will only cause it to be reloaded again
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// same if we don't get a new IL processor
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// and we do not want that (as it would mark the fields)
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var body = new MethodBody (method);
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var il = body.GetILProcessor ();
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il.Emit (OpCodes.Ret);
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method.Body = body;
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}
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public static void ReapplyDisposedFields (DerivedLinkContext context, string operation)
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{
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// note: all methods in the dictionary are marked (since they were added from an IMarkHandler)
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foreach ((var method, var body) in dispose) {
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foreach (var ins in body.Instructions) {
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switch (ins.OpCode.OperandType) {
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case OperandType.InlineField:
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var fr = ins.Operand as FieldReference;
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var field = fr?.Resolve ();
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var isMarked = field is not null && context.Annotations.IsMarked (field);
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if (!isMarked) {
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var store_field = ins;
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var load_null = ins.Previous;
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var load_this = ins.Previous.Previous;
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if (OptimizeGeneratedCodeHandler.ValidateInstruction (method, store_field, operation, Code.Stfld) &&
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OptimizeGeneratedCodeHandler.ValidateInstruction (method, load_null, operation, Code.Ldnull) &&
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OptimizeGeneratedCodeHandler.ValidateInstruction (method, load_this, operation, Code.Ldarg_0)) {
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store_field.OpCode = OpCodes.Nop;
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load_null.OpCode = OpCodes.Nop;
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load_this.OpCode = OpCodes.Nop;
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}
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}
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break;
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}
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}
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method.Body = body;
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}
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}
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}
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public class BackingFieldReintroductionSubStep : ExceptionalSubStep {
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public override SubStepTargets Targets => SubStepTargets.Assembly;
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protected override string Name => "Backing Field Reintroduction";
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protected override int ErrorCode { get; } = 2410;
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public override void Initialize (LinkContext context)
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{
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base.Initialize (context);
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BackingFieldDelayHandler.ReapplyDisposedFields (LinkContext, Name);
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}
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}
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}
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