[docs] Update optimizations document with upstream changes. (#4043)
Ref: https://github.com/MicrosoftDocs/xamarin-docs-pr/pull/204
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Rolf Bjarne Kvinge
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---
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id: 84B67E31-B217-443D-89E5-CFE1923CB14E
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title: Build optimizations
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dateupdated: 2018-01-18
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title: "Build optimizations"
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description: "This document explains the various optimizations that are applied at build time for Xamarin.iOS and Xamarin.Mac apps."
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ms.prod: xamarin
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ms.assetid: 84B67E31-B217-443D-89E5-CFE1923CB14E
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ms.technology: xamarin-cross-platform
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author: bradumbaugh
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ms.author: brumbaug
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dateupdated: 04/16/2018
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---
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[//]: # (The original file resides under https://github.com/xamarin/xamarin-macios/tree/master/docs/website/)
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[//]: # (This allows all contributors (including external) to submit, using a PR, updates to the documentation that match the tools changes)
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[//]: # (Modifications outside of xamarin-macios/master will be lost on future updates)
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# Build optimizations
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Build optimizations
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===================
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This document explains the various optimizations that are applied at build time for
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Xamarin.iOS and Xamarin.Mac apps.
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This document explains the various optimizations that are applied at build time for Xamarin.iOS and Xamarin.Mac apps.
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Remove UIApplication.EnsureUIThread / NSApplication.EnsureUIThread
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------------------------------------------------------------------
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## Remove UIApplication.EnsureUIThread / NSApplication.EnsureUIThread
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Removes calls to [UIApplication.EnsureUIThread][1] (for Xamarin.iOS) or
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`NSApplication.EnsureUIThread` (for Xamarin.Mac).
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@ -47,10 +47,9 @@ The default behavior can be overridden by passing `--optimize=[+|-]remove-uithre
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[1]: https://developer.xamarin.com/api/member/UIKit.UIApplication.EnsureUIThread/
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Inline IntPtr.Size
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------------------
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## Inline IntPtr.Size
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Inlines the constant value of IntPtr.Size according to the target platform.
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Inlines the constant value of `IntPtr.Size` according to the target platform.
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This optimization will change the following type of code:
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@ -76,26 +75,25 @@ This optimization requires the linker to be enabled, and is only applied to
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methods with the `[BindingImpl (BindingImplOptions.Optimizable)]` attribute.
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By default it's enabled if targeting a single architecture, or for the
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platform assembly (Xamarin.iOS.dll, Xamarin.TVOS.dll, Xamarin.WatchOS.dll or
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Xamarin.Mac.dll).
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platform assembly (**Xamarin.iOS.dll**, **Xamarin.TVOS.dll**,
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**Xamarin.WatchOS.dll** or **Xamarin.Mac.dll**).
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If targeting multiple architecture, this optimization will create different
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If targeting multiple architectures, this optimization will create different
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assemblies for the 32-bit version and the 64-bit version of the app, and both
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versions will have to be included in the app, effectively increasing the final
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app size instead of decreasing it.
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The default behavior can be overridden by passing `--optimize=[+|-]inline-intptr-size` to mtouch/mmp.
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Inline NSObject.IsDirectBinding
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-------------------------------
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## Inline NSObject.IsDirectBinding
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NSObject.IsDirectBinding is an instance property that determines whether a
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`NSObject.IsDirectBinding` is an instance property that determines whether a
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particular instance is of a wrapper type or not (a wrapper type is a managed
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type that maps to a native type; for instance the managed `UIKit.UIView` type
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maps to the native `UIView` type - the opposite is a user type, in this case
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`class MyUIView : UIKit.UIView` would be a user type).
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It's necessary to know the value of IsDirectBinding when calling into
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It's necessary to know the value of `IsDirectBinding` when calling into
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Objective-C, because the value determines which version of `objc_msgSend` to
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use.
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@ -130,7 +128,8 @@ class MyUIView : UIView {
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}
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```
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we can determine that in `UIView.SomeProperty` the value of `IsDirectBinding` is not a constant and can not be inlined:
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We can determine that in `UIView.SomeProperty` the value of
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`IsDirectBinding` is not a constant and cannot be inlined:
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```csharp
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void uiView = new UIView ();
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@ -139,7 +138,7 @@ void myView = new MyUIView ();
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Console.WriteLine (myView.SomeProperty); // prints 'false'
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```
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however it's possible to look at the all the types in the app and determine
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However, it's possible to look at the all the types in the app and determine
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that there are no types that inherit from `NSUrl`, and it's thus safe to
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inline the `IsDirectBinding` value to a constant `true`:
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@ -150,7 +149,7 @@ Console.WriteLine (myURL.SomeOtherProperty); // prints 'true'
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```
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In particular, this optimization will change the following type of code (this
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is the binding code for NSUrl.AbsoluteUrl):
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is the binding code for `NSUrl.AbsoluteUrl`):
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```csharp
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if (IsDirectBinding) {
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@ -161,7 +160,7 @@ if (IsDirectBinding) {
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```
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into the following (when it can be determined that there are no subclasses of
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NSUrl in the app):
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`NSUrl` in the app):
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```csharp
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if (true) {
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@ -179,10 +178,10 @@ default for Xamarin.Mac (because it's possible to dynamically load assemblies
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in Xamarin.Mac, it's not possible to determine that a particular class is
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never subclassed).
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The default behavior can be overridden by passing `--optimize=[+|-]inline-isdirectbinding` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=[+|-]inline-isdirectbinding` to mtouch/mmp.
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Inline Runtime.Arch
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-------------------
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## Inline Runtime.Arch
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This optimization will change the following type of code:
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@ -210,10 +209,10 @@ methods with the `[BindingImpl (BindingImplOptions.Optimizable)]` attribute.
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It is always enabled by default for Xamarin.iOS (it's not available for
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Xamarin.Mac).
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The default behavior can be overridden by passing `--optimize=[+|-]inline-runtime-arch` to mtouch.
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The default behavior can be overridden by passing
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`--optimize=[+|-]inline-runtime-arch` to mtouch.
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Dead code elimination
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---------------------
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## Dead code elimination
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This optimization will change the following type of code:
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@ -249,7 +248,7 @@ Console.WriteLine ("Doing this");
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This is a powerful optimization when used together with the inlining
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optimizations, because it can transform the following type of code (this is
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the binding code for NFCIso15693ReadMultipleBlocksConfiguration.Range):
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the binding code for `NFCIso15693ReadMultipleBlocksConfiguration.Range`):
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```csharp
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NSRange ret;
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@ -281,7 +280,9 @@ if (IsDirectBinding) {
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return ret;
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```
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into this (when building for a 64-bit device, and when also able to ensure there are no NFCIso15693ReadMultipleBlocksConfiguration subclasses in the app):
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into this (when building for a 64-bit device, and when also able to
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ensure there are no `NFCIso15693ReadMultipleBlocksConfiguration` subclasses
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in the app):
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```csharp
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NSRange ret;
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@ -294,19 +295,19 @@ optimization is done inside the linker, which means that the linker able to
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see that there are multiple methods that are not used anymore, and may thus be
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removed (unless used elsewhere):
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* global::ObjCRuntime.Messaging.NSRange_objc_msgSend_stret
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* global::ObjCRuntime.Messaging.NSRange_objc_msgSendSuper
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* global::ObjCRuntime.Messaging.NSRange_objc_msgSendSuper_stret
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* `global::ObjCRuntime.Messaging.NSRange_objc_msgSend_stret`
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* `global::ObjCRuntime.Messaging.NSRange_objc_msgSendSuper`
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* `global::ObjCRuntime.Messaging.NSRange_objc_msgSendSuper_stret`
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This optimization requires the linker to be enabled, and is only applied to
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methods with the `[BindingImpl (BindingImplOptions.Optimizable)]` attribute.
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It is always enabled by default (when the linker is enabled).
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The default behavior can be overridden by passing `--optimize=[+|-]dead-code-elimination` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=[+|-]dead-code-elimination` to mtouch/mmp.
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Optimize calls to BlockLiteral.SetupBlock
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-----------------------------------------
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## Optimize calls to BlockLiteral.SetupBlock
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The Xamarin.iOS/Mac runtime needs to know the block signature when creating an
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Objective-C block for a managed delegate. This might be a fairly expensive
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@ -346,10 +347,10 @@ It is enabled by default when using the static registrar (in Xamarin.iOS the
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static registrar is enabled by default for device builds, and in Xamarin.Mac
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the static registrar is enabled by default for release builds).
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The default behavior can be overridden by passing `--optimize=[+|-]blockliteral-setupblock` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=[+|-]blockliteral-setupblock` to mtouch/mmp.
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Optimize support for protocols
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------------------------------
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## Optimize support for protocols
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The Xamarin.iOS/Mac runtime needs information about how managed types
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implements Objective-C protocols. This information is stored in interfaces
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@ -379,10 +380,10 @@ On Xamarin.Mac this optimization is never enabled by default, because
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Xamarin.Mac supports loading assemblies dynamically, and those assemblies
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might not have been known at build time (and thus not optimized).
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The default behavior can be overridden by passing `--optimize=-register-protocols` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=-register-protocols` to mtouch/mmp.
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Remove the dynamic registrar
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----------------------------
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## Remove the dynamic registrar
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Both the Xamarin.iOS and the Xamarin.Mac runtime include support for
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[registering managed types](https://developer.xamarin.com/guides/ios/advanced_topics/registrar/)
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@ -403,21 +404,21 @@ were not known at build time), it's impossible to determine at build time
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whether this is a safe optimization. This means that this optimization is
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never enabled by default for Xamarin.Mac apps.
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The default behavior can be overridden by passing `--optimize=[+|-]remove-dynamic-registrar` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=[+|-]remove-dynamic-registrar` to mtouch/mmp.
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If the default is overridden to remove the dynamic registrar, the linker will
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emit warnings if it detects that it's not safe (but the dynamic registrar will
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still be removed).
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Inline Runtime.DynamicRegistrationSupported
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-------------------------------------------
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## Inline Runtime.DynamicRegistrationSupported
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Inlines the value of Runtime.DynamicRegistrationSupported as determined at
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Inlines the value of `Runtime.DynamicRegistrationSupported` as determined at
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build time.
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If the dynamic registrar is removed (see the "Remove the dynamic registrar"
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optimization), this is a constant 'false' value, otherwise it's a constant
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'true' value.
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If the dynamic registrar is removed (see the [Remove the dynamic
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registrar](#remove-the-dynamic-registrar) optimization), this is a
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constant `false` value, otherwise it's a constant `true` value.
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This optimization will change the following type of code:
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@ -446,10 +447,10 @@ methods with the `[BindingImpl (BindingImplOptions.Optimizable)]` attribute.
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It is always enabled by default (when the linker is enabled).
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The default behavior can be overridden by passing `--optimize=[+|-]inline-dynamic-registration-supported` to mtouch/mmp.
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The default behavior can be overridden by passing
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`--optimize=[+|-]inline-dynamic-registration-supported` to mtouch/mmp.
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Precompute methods to create managed delegates for Objective-C blocks
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---------------------------------------------------------------------
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## Precompute methods to create managed delegates for Objective-C blocks
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When Objective-C calls a selector that takes a block as a parameter, and then
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managed code has overriden that method, the Xamarin.iOS / Xamarin.Mac runtime
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@ -461,12 +462,13 @@ can do this.
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Given the following Objective-C code:
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```objective-c
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```objc
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@interface ObjCBlockTester : NSObject {
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}
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-(void) classCallback: (void (^)())completionHandler;
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-(void) callClassCallback;
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@end
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@implementation ObjCBlockTester
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-(void) classCallback: (void (^)())completionHandler
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{
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