JIT: remove boxing for interface call to shared generic struct

src/jit/compiler.h

@@ -2270,7 +2270,8 @@ class Compiler
         BR_REMOVE_AND_NARROW, // remove effects, minimize remaining work, return possibly narrowed source tree
         BR_REMOVE_AND_NARROW_WANT_TYPE_HANDLE, // remove effects and minimize remaining work, return type handle tree
         BR_REMOVE_BUT_NOT_NARROW,              // remove effects, return original source tree
-        BR_DONT_REMOVE,                        // just check if removal is possible
+        BR_DONT_REMOVE,                        // check if removal is possible, return copy source tree
+        BR_DONT_REMOVE_WANT_TYPE_HANDLE,       // check if removal is possible, return type handle tree
         BR_MAKE_LOCAL_COPY                     // revise box to copy to temp local and return local's address
     };
 

src/jit/gentree.cpp

@@ -13468,7 +13468,7 @@ GenTree* Compiler::gtTryRemoveBoxUpstreamEffects(GenTree* op, BoxRemovalOptions
 
     // If we're eventually going to return the type handle, remember it now.
     GenTree* boxTypeHandle = nullptr;
-    if (options == BR_REMOVE_AND_NARROW_WANT_TYPE_HANDLE)
+    if ((options == BR_REMOVE_AND_NARROW_WANT_TYPE_HANDLE) || (options == BR_DONT_REMOVE_WANT_TYPE_HANDLE))
     {
         GenTree*   asgSrc     = asg->gtOp.gtOp2;
         genTreeOps asgSrcOper = asgSrc->OperGet();
@@ -13632,6 +13632,11 @@ GenTree* Compiler::gtTryRemoveBoxUpstreamEffects(GenTree* op, BoxRemovalOptions
         return copySrc;
     }
 
+    if (options == BR_DONT_REMOVE_WANT_TYPE_HANDLE)
+    {
+        return boxTypeHandle;
+    }
+
     // Otherwise, proceed with the optimization.
     //
     // Change the assignment expression to a NOP.

src/jit/importer.cpp

@@ -19502,8 +19502,8 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
     }
 
     // Fetch method attributes to see if method is marked final.
-    const DWORD derivedMethodAttribs = info.compCompHnd->getMethodAttribs(derivedMethod);
-    const bool  derivedMethodIsFinal = ((derivedMethodAttribs & CORINFO_FLG_FINAL) != 0);
+    DWORD      derivedMethodAttribs = info.compCompHnd->getMethodAttribs(derivedMethod);
+    const bool derivedMethodIsFinal = ((derivedMethodAttribs & CORINFO_FLG_FINAL) != 0);
 
 #if defined(DEBUG)
     const char* derivedClassName  = "?derivedClass";
@@ -19597,7 +19597,6 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
         JITDUMP("Now have direct call to boxed entry point, looking for unboxed entry point\n");
 
         // Note for some shared methods the unboxed entry point requires an extra parameter.
-        // We defer optimizing if so.
         bool                  requiresInstMethodTableArg = false;
         CORINFO_METHOD_HANDLE unboxedEntryMethod =
             info.compCompHnd->getUnboxedEntry(derivedMethod, &requiresInstMethodTableArg);
@@ -19614,9 +19613,57 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
             // the copy, we can undo the copy too.
             if (requiresInstMethodTableArg)
             {
-                // We can likely handle this case by grabbing the argument passed to
-                // the newobj in the box. But defer for now.
-                JITDUMP("Found unboxed entry point, but it needs method table arg, deferring\n");
+                // Perform a trial box removal and ask for the type handle tree.
+                JITDUMP("Unboxed entry needs method table arg...\n");
+                GenTree* methodTableArg = gtTryRemoveBoxUpstreamEffects(thisObj, BR_DONT_REMOVE_WANT_TYPE_HANDLE);
+
+                if (methodTableArg != nullptr)
+                {
+                    // If that worked, turn the box into a copy to a local var
+                    JITDUMP("Found suitable method table arg tree [%06u]\n", dspTreeID(methodTableArg));
+                    GenTree* localCopyThis = gtTryRemoveBoxUpstreamEffects(thisObj, BR_MAKE_LOCAL_COPY);
+
+                    if (localCopyThis != nullptr)
+                    {
+                        // Pass the local var as this and the type handle as a new arg
+                        JITDUMP("Success! invoking unboxed entry point on local copy, and passing method table arg\n");
+                        call->gtCallObjp = localCopyThis;
+
+                        // Prepend for R2L arg passing or empty L2R passing
+                        if ((Target::g_tgtArgOrder == Target::ARG_ORDER_R2L) || (call->gtCallArgs == nullptr))
+                        {
+                            call->gtCallArgs = gtNewListNode(methodTableArg, call->gtCallArgs);
+                        }
+                        // Append for non-empty L2R
+                        else
+                        {
+                            GenTreeArgList* beforeArg = call->gtCallArgs;
+                            while (beforeArg->Rest() != nullptr)
+                            {
+                                beforeArg = beforeArg->Rest();
+                            }
+
+                            beforeArg->Rest() = gtNewListNode(methodTableArg, nullptr);
+                        }
+
+                        call->gtCallMethHnd = unboxedEntryMethod;
+                        derivedMethod       = unboxedEntryMethod;
+
+                        // Method attributes will differ because unboxed entry point is shared
+                        const DWORD unboxedMethodAttribs = info.compCompHnd->getMethodAttribs(unboxedEntryMethod);
+                        JITDUMP("Updating method attribs from 0x%08x to 0x%08x\n", derivedMethodAttribs,
+                                unboxedMethodAttribs);
+                        derivedMethodAttribs = unboxedMethodAttribs;
+                    }
+                    else
+                    {
+                        JITDUMP("Sorry, failed to undo the box -- can't convert to local copy\n");
+                    }
+                }
+                else
+                {
+                    JITDUMP("Sorry, failed to undo the box -- can't find method table arg\n");
+                }
             }
             else
             {

tests/src/JIT/opt/Devirtualization/box1.cs

@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+interface IPrint 
+{
+    void Print();
+}
+
+struct X<T> : IPrint
+{
+    public X(T t) { _t = t; }
+    public void Print() { Console.WriteLine(_t); }
+    T _t;
+}
+
+class Y
+{
+    static int Main()
+    {
+        var s = new X<string>("hello, world!");
+        // Jit should devirtualize, remove box,
+        // change to call unboxed entry, then inline.
+        ((IPrint)s).Print();
+        return 100;
+    }
+}

tests/src/JIT/opt/Devirtualization/box1.csproj

@@ -0,0 +1,34 @@
+<?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>$(MSBuildProjectName)</AssemblyName>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="box1.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>

tests/src/JIT/opt/Devirtualization/box2.cs

@@ -0,0 +1,24 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+class Program
+{
+    static async Task<int> Main()
+    {
+        for (int i = 0; i < 10; i++)
+        {
+            // In the associated AwaitUnsafeOnCompleted, the 
+            // jit should devirtualize, remove the box,
+            // and change to call unboxed entry, passing
+            // extra context argument.
+            await new ValueTask<string>(Task.Delay(1).ContinueWith(_ => default(string))).ConfigureAwait(false);
+        }
+
+        return 100;
+    }
+}

tests/src/JIT/opt/Devirtualization/box2.csproj

@@ -0,0 +1,35 @@
+<?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>$(MSBuildProjectName)</AssemblyName>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <Langversion>7.2</Langversion>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="box2.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>