[dotnet][linker] Remove unused backing fields (#12001)
Problems:
* `Dispose` set the generated backing fields to `null` which means
the linker will mark every backing fields, even if not used
elsewhere (generally properties) inside the class
* Backing fields increase the memory footprint of the managed peer
instance (for the type and all it's subclasses)
* Backing fields also increase the app size. Not a huge problem as
they are all declared _weakly_ as `NSObject` but still...
Solution:
* When the linker process a `Dispose` method of an `NSObject`
subclass with the _optimizable_ attribute then we remove the
method body. This way the linker cannot mark the fields.
* Before saving back the assemblies we replace the cached method
body and NOP every field that were not marked by something else
than the `Dispose` method.
```diff
--- a.cs 2021-06-22 16:56:57.000000000 -0400
+++ b.cs 2021-06-22 16:57:00.000000000 -0400
@@ -3107,8 +3107,6 @@
private static readonly IntPtr class_ptr = Class.GetHandle("UIApplication");
- private object __mt_WeakDelegate_var;
-
public override IntPtr ClassHandle => class_ptr;
[DllImport("__Internal")]
@@ -3141,9 +3139,8 @@
protected override void Dispose(bool P_0)
{
base.Dispose(P_0);
- if (base.Handle == IntPtr.Zero)
+ if (!(base.Handle == IntPtr.Zero))
{
- __mt_WeakDelegate_var = null;
}
}
}
@@ -3209,10 +3206,6 @@
{
private static readonly IntPtr class_ptr = Class.GetHandle("UIScreen");
- private object __mt_FocusedItem_var;
-
- private object __mt_FocusedView_var;
-
public override IntPtr ClassHandle => class_ptr;
public virtual CGRect Bounds
@@ -3242,10 +3235,8 @@
protected override void Dispose(bool P_0)
{
base.Dispose(P_0);
- if (base.Handle == IntPtr.Zero)
+ if (!(base.Handle == IntPtr.Zero))
{
- __mt_FocusedItem_var = null;
- __mt_FocusedView_var = null;
}
}
}
@@ -3254,10 +3245,6 @@
{
private static readonly IntPtr class_ptr = Class.GetHandle("UIView");
- private object __mt_ParentFocusEnvironment_var;
-
- private object __mt_PreferredFocusedView_var;
-
public override IntPtr ClassHandle => class_ptr;
public virtual CGRect Bounds
@@ -3303,10 +3290,8 @@
protected override void Dispose(bool P_0)
{
base.Dispose(P_0);
- if (base.Handle == IntPtr.Zero)
+ if (!(base.Handle == IntPtr.Zero))
{
- __mt_ParentFocusEnvironment_var = null;
- __mt_PreferredFocusedView_var = null;
}
}
}
@@ -3315,12 +3300,6 @@
{
private static readonly IntPtr class_ptr = Class.GetHandle("UIViewController");
- private object __mt_ParentFocusEnvironment_var;
-
- private object __mt_PreferredFocusedView_var;
-
- private object __mt_WeakTransitioningDelegate_var;
-
public override IntPtr ClassHandle => class_ptr;
public virtual UIView View
@@ -3363,11 +3342,8 @@
protected override void Dispose(bool P_0)
{
base.Dispose(P_0);
- if (base.Handle == IntPtr.Zero)
+ if (!(base.Handle == IntPtr.Zero))
{
- __mt_ParentFocusEnvironment_var = null;
- __mt_PreferredFocusedView_var = null;
- __mt_WeakTransitioningDelegate_var = null;
}
}
}
@@ -3376,8 +3352,6 @@
{
private static readonly IntPtr class_ptr = Class.GetHandle("UIWindow");
- private object __mt_WindowScene_var;
-
public override IntPtr ClassHandle => class_ptr;
public virtual UIViewController RootViewController
@@ -3411,9 +3385,8 @@
protected override void Dispose(bool P_0)
{
base.Dispose(P_0);
- if (base.Handle == IntPtr.Zero)
+ if (!(base.Handle == IntPtr.Zero))
{
- __mt_WindowScene_var = null;
}
}
}
```
* Do not consider bindings with `[Dispose (...)]` as optimizable
Injected code makes it impossible for `bgen` to decide if it's optimizable (or not)
Filed https://github.com/xamarin/xamarin-macios/issues/12150 with more details (and for other similar attributes)
This commit is contained in:
Sebastien Pouliot
GitHub
Родитель
f521537e0a
Коммит
fccd43f0c2
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@ -459,6 +459,7 @@
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-->
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<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_LinkMode)' != 'None'" Type="Xamarin.Linker.Steps.PreserveBlockCodeHandler" />
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<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_LinkMode)' != 'None'" Type="Xamarin.Linker.OptimizeGeneratedCodeHandler" />
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<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_LinkMode)' != 'None'" Type="Xamarin.Linker.BackingFieldDelayHandler" />
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<!-- MarkDispatcher substeps will run for all marked assemblies. -->
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<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_LinkMode)' != 'None'" Type="Xamarin.Linker.Steps.MarkDispatcher" />
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<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_LinkMode)' != 'None'" Type="Xamarin.Linker.Steps.PreserveSmartEnumConversionsHandler" />
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@ -3143,11 +3143,14 @@ public partial class Generator : IMemberGatherer {
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// this attribute allows the linker to be more clever in removing unused code in bindings - without risking breaking user code
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// only generate those for monotouch now since we can ensure they will be linked away before reaching the devices
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public void GeneratedCode (StreamWriter sw, int tabs)
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public void GeneratedCode (StreamWriter sw, int tabs, bool optimizable = true)
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{
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for (int i=0; i < tabs; i++)
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sw.Write ('\t');
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sw.WriteLine ("[BindingImpl (BindingImplOptions.GeneratedCode | BindingImplOptions.Optimizable)]");
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sw.Write ("[BindingImpl (BindingImplOptions.GeneratedCode");
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if (optimizable)
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sw.Write (" | BindingImplOptions.Optimizable");
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sw.WriteLine (")]");
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}
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static void WriteIsDirectBindingCondition (StreamWriter sw, ref int tabs, bool? is_direct_binding, string is_direct_binding_value, Func<string> trueCode, Func<string> falseCode)
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@ -3184,9 +3187,9 @@ public partial class Generator : IMemberGatherer {
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}
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}
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public void print_generated_code ()
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public void print_generated_code (bool optimizable = true)
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{
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GeneratedCode (sw, indent);
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GeneratedCode (sw, indent, optimizable);
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}
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public void print (string format)
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@ -7422,7 +7425,7 @@ public partial class Generator : IMemberGatherer {
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if (!is_static_class){
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var disposeAttr = AttributeManager.GetCustomAttributes<DisposeAttribute> (type);
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if (disposeAttr.Length > 0 || instance_fields_to_clear_on_dispose.Count > 0){
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print_generated_code ();
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print_generated_code (optimizable: disposeAttr.Length == 0);
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print ("protected override void Dispose (bool disposing)");
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print ("{");
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indent++;
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@ -0,0 +1,105 @@
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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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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 field = (ins.Operand as FieldReference)?.Resolve ();
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if (!context.Annotations.IsMarked (field)) {
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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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@ -4,7 +4,10 @@ using Xamarin.Linker;
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namespace Xamarin.Linker.Steps {
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class PreOutputDispatcher : SubStepsDispatcher {
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public PreOutputDispatcher ()
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: base (new [] { new RemoveUserResourcesSubStep () })
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: base (new BaseSubStep [] {
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new RemoveUserResourcesSubStep (),
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new BackingFieldReintroductionSubStep (),
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})
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{
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}
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}
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@ -218,7 +218,7 @@ namespace Xamarin.Linker {
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ins.Operand = null;
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}
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protected static bool ValidateInstruction (MethodDefinition caller, Instruction ins, string operation, Code expected)
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internal static bool ValidateInstruction (MethodDefinition caller, Instruction ins, string operation, Code expected)
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{
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if (ins.OpCode.Code != expected) {
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Driver.Log (1, "Could not {0} in {1} at offset {2}, expected {3} got {4}", operation, caller, ins.Offset, expected, ins);
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@ -228,7 +228,7 @@ namespace Xamarin.Linker {
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return true;
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}
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protected static bool ValidateInstruction (MethodDefinition caller, Instruction ins, string operation, params Code [] expected)
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internal static bool ValidateInstruction (MethodDefinition caller, Instruction ins, string operation, params Code [] expected)
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{
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foreach (var code in expected) {
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if (ins.OpCode.Code == code)
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