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.NET Framework 4.6 - Testing RyuJIT

The .NET Framework 4.6 includes new Just-In-Time (JIT) compiler for 64-bit processes, called RyuJIT. It is enabled by default.

This document provides instructions to disable RyuJIT or one of its optimizations, in order to test your program without it running. This is useful if you experience unexpected product behavior and want to determine if RyuJIT is the cause of that behavioral change.

Disable RyuJIT

Important Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

Note For all these methods, all dynamic compilation is performed by the older JIT64 JIT. Also, all NGEN compilation continues to use the new JIT, and all existing NGEN images that have been compiled by the new JIT continue to be used.

Method 1. Set the following environment variable:
```
  COMPLUS_useLegacyJit=1
```

Method 2. In the registry, create either of the following subkeys:

  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework
  HKEY_CURRENT_USER\SOFTWARE\Microsoft\.NETFramework

Then, specify the following:

  Key name: useLegacyJit
  Type: REG_WORD
  Value: 1

Method 3. Add the following text to the <app>.exe.config file. Create the indicated sections if they do not already exist.

Note In this file name, <app> represents the actual name of the application.
```
  <configuration>
    <runtime>
     <useLegacyJit enabled="1">
    </runtime>
  </configuration>
```

Disable loading NGEN Images

If you encounter a bug when you use the new JIT, and if the bug manifests itself as an NGEN image, use any of the following methods to force certain named assemblies to be recompiled by the JIT and not use the existing native images:

Method 1. Set the following environment variable:

  COMPLUS_DisableNativeImageLoadList=assembly_one;assembly_two;assembly_three

Method 2. In the registry, create either of the following subkeys:
```
  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework
  HKEY_CURRENT_USER\SOFTWARE\Microsoft\.NETFramework
```
Then, specify the following:
```
  Key name: DisableNativeImageLoadList
  Type: REG_SZ
  Value: assembly_one;assembly_two;assembly_three
```
Note This is a semicolon-delimited or space-delimited list of simple assembly names (no public key token, no architecture, and so on). This list does not contain the .dll file name extension. In the examples in this method and the next method, assembly_one is the simple name for an assembly that is named assembly_one.dll.

Method 3. Add the following text to the <app>.exe.config file. Create the indicated sections if they do not already exist.

Note In this file name, <app> represents the actual name of the application.

<configuration>
  <runtime>
   <disableNativeImageLoad>
    <assemblyIdentity name="assembly_one" />
    <assemblyIdentity name="assembly_two" />
  </disableNativeImageLoad>
  </runtime>
</configuration>

Disable Tail Call Optimization

You can disable tail call optimization in RyuJIT with the following instructions.

In the registry, create either of the following subkeys:

  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework
  HKEY_CURRENT_USER\SOFTWARE\Microsoft\.NETFramework