Fix for potential bad tailcall code generation

src/jit/lower.cpp

@@ -1727,6 +1727,8 @@ void Lowering::LowerFastTailCall(GenTreeCall *call)
                    }

                    lcl->SetLclNum(tmpLclNum);
                    lcl->SetOper(GT_LCL_VAR);

                }                
            }
        }

tests/src/JIT/Regression/JitBlue/GitHub_1296/GitHub_1296.cs

@@ -0,0 +1,89 @@
using System;

// Simple struct containing two integers (size 8).
struct MyStruct
{
    public MyStruct(int a, int b)
    {
        A = a;
        B = b;
    }

    public int A;
    public int B;
    public int C { get { return A + B; } }
}

class Program
{

    static int Pass = 100;
    static int Fail = -1;
    static int Main(string[] args)
    {
        // Entry point for our repro.
        // Pass in a bunch of integers.  The 5th parameter is a MyStruct, a value type of size 8.
        int result = Caller(0, 1, 2, 3, new MyStruct(4, 5));
        if (result != 9)
        {
            Console.WriteLine("Fail");
            return Fail;
        }
        else
        {
            Console.WriteLine("Pass");
            return Pass;
        }
    }

    // Caller method takes 5 parameters.  4 in register and 1 on the stack.  The important details here are that
    //  * Must take a value type as a parameter
    //  * The value type must be of size 1, 2, 4 or 8
    //  * That parameter must be passed on the stack.  Typically this is the 5th parameter and beyond for
    //    static methods, or 4th and beyond for instance methods.
    static int Caller(int regParam1, int regParam2, int regParam3, int regParam4, MyStruct stackParam1)
    {
        // Add random calls to block inlining of this call into the parent frame.
        Console.Write("Let's ");
        Console.Write("Discourage ");
        Console.Write("Inlining ");
        Console.Write("Of ");
        Console.Write("Caller ");
        Console.Write("Into ");
        Console.WriteLine("Main.");

        // Avoid touching stackParam1 except to pass it off to the callee.  Any non-trivial usage of
        // stackParam1 or other code within this method will likely eliminate the potential for tail
        // call optimization.
        // if (stackParam1.C == 9) Console.WriteLine("C == 9");

        // Now make our call.
        // The keys here are:
        //  * That the incoming value type stack parameter must be passed to the callee in register.
        //  * Tail call optimizations must be enabled
        //  * The tail call optimization must fire (see above for an example of what might block it).
        // The JIT will incorrectly load the outgoing parameter from the incorrect stack location
        // on the local frame.
        return Callee(stackParam1, regParam1, regParam2, regParam3, regParam4);
    }

    // Callee method takes 5 parameters.  4 in register and 1 on the stack.  The important details here are that
    //  * Must take a value type as a parameter
    //  * The value type must be of size 1, 2, 4 or 8
    //  * That parameter must be passed in register.  Typically this is the 4th parameter or before for
    //    static methods, or 3rd or before for instance methods.
    static int Callee(MyStruct regParam1, int regParam2, int regParam3, int regParam4, int stackParam1)
    {
        // If all conditions are met, Callee enters with an incorrect value for regParam1
        // This should print "9 0 1 2 3".  If the tail call is made incorrectly,
        // the result is (typically) "418858424 0 1 2 3".
        System.Console.WriteLine("Printing Outputs: {0} {1} {2} {3} {4}",
            regParam1.C,
            regParam2,
            regParam3,
            regParam4,
            stackParam1);

        return regParam1.C;
    }
}

tests/src/JIT/Regression/JitBlue/GitHub_1296/GitHub_1296.csproj

@@ -0,0 +1,50 @@
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <AssemblyName>$(MSBuildProjectName)</AssemblyName>
    <SchemaVersion>2.0</SchemaVersion>
    <ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
    <OutputType>Exe</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <FileAlignment>512</FileAlignment>
    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
    <ReferencePath>$(ProgramFiles)\Common Files\microsoft shared\VSTT\11.0\UITestExtensionPackages</ReferencePath>
    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>

    <NuGetPackageImportStamp>7a9bfb7d</NuGetPackageImportStamp>
  </PropertyGroup>
  <!-- Default configurations to help VS understand the configurations -->
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
  </PropertyGroup>
  <ItemGroup>
    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
      <Visible>False</Visible>
    </CodeAnalysisDependentAssemblyPaths>
  </ItemGroup>
  <PropertyGroup>
    <DebugType></DebugType>
    <Optimize>True</Optimize>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="$(MSBuildProjectName).cs" />
  </ItemGroup>
  <ItemGroup>
    <None Include="$(JitPackagesConfigFileDirectory)minimal\project.json" />
    <None Include="app.config" />
  </ItemGroup>
  <ItemGroup>
    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
  </ItemGroup>
  <PropertyGroup>
    <ProjectJson>$(JitPackagesConfigFileDirectory)minimal\project.json</ProjectJson>
    <ProjectLockJson>$(JitPackagesConfigFileDirectory)minimal\project.lock.json</ProjectLockJson>
  </PropertyGroup>
  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' ">
  </PropertyGroup> 
</Project>

tests/src/JIT/Regression/JitBlue/GitHub_1296/app.config

@@ -0,0 +1,27 @@
<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
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      <dependentAssembly>
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        <bindingRedirect oldVersion="0.0.0.0-4.0.10.0" newVersion="4.0.10.0" />
      </dependentAssembly>
      <dependentAssembly>
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        <bindingRedirect oldVersion="0.0.0.0-4.0.10.0" newVersion="4.0.10.0" />
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  </runtime>
</configuration>