JIT: streamline temp usage for returns (#20640)

If the jit decides it needs a return spill temp, and the return value has already been spilled to a single-def temp, re-use the existing for the return temp rather than creating a new one. In conjunction with #20553 this allows late devirtualization for calls where the object in the virtual call is the result of an inline that provides a better type, and the objected formerly reached the call via one or more intermediate temps. Closes #15873.
dotnet · Oct 29, 2018 · ccc18a6 · ccc18a6
1 parent 17879df
commit ccc18a6
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Showing 7 changed files with 208 additions and 19 deletions.
diff --git a/src/jit/flowgraph.cpp b/src/jit/flowgraph.cpp
@@ -5853,19 +5853,34 @@ void Compiler::fgFindBasicBlocks()
         // or if the inlinee has GC ref locals.
         if ((info.compRetNativeType != TYP_VOID) && ((retBlocks > 1) || impInlineInfo->HasGcRefLocals()))
         {
-            // The lifetime of this var might expand multiple BBs. So it is a long lifetime compiler temp.
-            lvaInlineeReturnSpillTemp                  = lvaGrabTemp(false DEBUGARG("Inline return value spill temp"));
-            lvaTable[lvaInlineeReturnSpillTemp].lvType = info.compRetNativeType;
+            // If we've spilled the ret expr to a temp we can reuse the temp
+            // as the inlinee return spill temp.
+            //
+            // Todo: see if it is even better to always use this existing temp
+            // for return values, even if we otherwise wouldn't need a return spill temp...
+            lvaInlineeReturnSpillTemp = impInlineInfo->inlineCandidateInfo->preexistingSpillTemp;
 
-            // If the method returns a ref class, set the class of the spill temp
-            // to the method's return value. We may update this later if it turns
-            // out we can prove the method returns a more specific type.
-            if (info.compRetType == TYP_REF)
+            if (lvaInlineeReturnSpillTemp != BAD_VAR_NUM)
+            {
+                // This temp should already have the type of the return value.
+                JITDUMP("\nInliner: re-using pre-existing spill temp V%02u\n", lvaInlineeReturnSpillTemp);
+            }
+            else
             {
-                CORINFO_CLASS_HANDLE retClassHnd = impInlineInfo->inlineCandidateInfo->methInfo.args.retTypeClass;
-                if (retClassHnd != nullptr)
+                // The lifetime of this var might expand multiple BBs. So it is a long lifetime compiler temp.
+                lvaInlineeReturnSpillTemp = lvaGrabTemp(false DEBUGARG("Inline return value spill temp"));
+                lvaTable[lvaInlineeReturnSpillTemp].lvType = info.compRetNativeType;
+
+                // If the method returns a ref class, set the class of the spill temp
+                // to the method's return value. We may update this later if it turns
+                // out we can prove the method returns a more specific type.
+                if (info.compRetType == TYP_REF)
                 {
-                    lvaSetClass(lvaInlineeReturnSpillTemp, retClassHnd);
+                    CORINFO_CLASS_HANDLE retClassHnd = impInlineInfo->inlineCandidateInfo->methInfo.args.retTypeClass;
+                    if (retClassHnd != nullptr)
+                    {
+                        lvaSetClass(lvaInlineeReturnSpillTemp, retClassHnd);
+                    }
                 }
             }
         }

diff --git a/src/jit/importer.cpp b/src/jit/importer.cpp
@@ -2219,6 +2219,16 @@ bool Compiler::impSpillStackEntry(unsigned level,
     {
         CORINFO_CLASS_HANDLE stkHnd = verCurrentState.esStack[level].seTypeInfo.GetClassHandle();
         lvaSetClass(tnum, tree, stkHnd);
+
+        // If we're assigning a GT_RET_EXPR, note the temp over on the call,
+        // so the inliner can use it in case it needs a return spill temp.
+        if (tree->OperGet() == GT_RET_EXPR)
+        {
+            JITDUMP("\n*** see V%02u = GT_RET_EXPR, noting temp\n", tnum);
+            GenTree*             call = tree->gtRetExpr.gtInlineCandidate;
+            InlineCandidateInfo* ici  = call->gtCall.gtInlineCandidateInfo;
+            ici->preexistingSpillTemp = tnum;
+        }
     }
 
     // The tree type may be modified by impAssignTempGen, so use the type of the lclVar.
@@ -18047,15 +18057,16 @@ void Compiler::impCheckCanInline(GenTree*               call,
             InlineCandidateInfo* pInfo;
             pInfo = new (pParam->pThis, CMK_Inlining) InlineCandidateInfo;
 
-            pInfo->dwRestrictions  = dwRestrictions;
-            pInfo->methInfo        = methInfo;
-            pInfo->methAttr        = pParam->methAttr;
-            pInfo->clsHandle       = clsHandle;
-            pInfo->clsAttr         = clsAttr;
-            pInfo->fncRetType      = fncRetType;
-            pInfo->exactContextHnd = pParam->exactContextHnd;
-            pInfo->ilCallerHandle  = pParam->pThis->info.compMethodHnd;
-            pInfo->initClassResult = initClassResult;
+            pInfo->dwRestrictions       = dwRestrictions;
+            pInfo->methInfo             = methInfo;
+            pInfo->methAttr             = pParam->methAttr;
+            pInfo->clsHandle            = clsHandle;
+            pInfo->clsAttr              = clsAttr;
+            pInfo->fncRetType           = fncRetType;
+            pInfo->exactContextHnd      = pParam->exactContextHnd;
+            pInfo->ilCallerHandle       = pParam->pThis->info.compMethodHnd;
+            pInfo->initClassResult      = initClassResult;
+            pInfo->preexistingSpillTemp = BAD_VAR_NUM;
 
             *(pParam->ppInlineCandidateInfo) = pInfo;
 

diff --git a/src/jit/inline.h b/src/jit/inline.h
@@ -509,6 +509,7 @@ struct InlineCandidateInfo
     CORINFO_CONTEXT_HANDLE exactContextHnd;
     bool                   exactContextNeedsRuntimeLookup;
     CorInfoInitClassResult initClassResult;
+    unsigned               preexistingSpillTemp;
 };
 
 // InlArgInfo describes inline candidate argument properties.

diff --git a/tests/src/JIT/opt/Devirtualization/arraypool.cs b/tests/src/JIT/opt/Devirtualization/arraypool.cs
@@ -0,0 +1,41 @@
+// 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.Buffers;
+using System.Runtime.CompilerServices;
+
+class X
+{
+    static int N;
+    static int J;
+    static int K;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static void S() { J = N / 2; K = J; }
+
+    // We expect calls to Rent and Return to be 
+    // devirtualized.
+    public static int Main()
+    {
+        N = 100;
+        byte[] buffer = ArrayPool<byte>.Shared.Rent(N);
+        int r = -1;
+
+        try {
+            S();
+            buffer[J] = 100;
+            r = (int) buffer[K];
+        }
+        finally
+        {
+            if (buffer != null)
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
+        }
+
+        return r;
+    }
+}
diff --git a/tests/src/JIT/opt/Devirtualization/arraypool.csproj b/tests/src/JIT/opt/Devirtualization/arraypool.csproj
@@ -0,0 +1,38 @@
+<?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	.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="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="arraypool.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>
diff --git a/tests/src/JIT/opt/Devirtualization/late1.cs b/tests/src/JIT/opt/Devirtualization/late1.cs
@@ -0,0 +1,45 @@
+// 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.Runtime.CompilerServices;
+
+public class B
+{
+    public virtual int F(int x) { return x + 33; }
+}
+
+public class D : B
+{
+    public override int F(int x) { return x + 44; }
+}
+
+public class Q
+{
+    static int V(int x)
+    {
+        return x;
+    }
+
+    // calls to B will use a return spill temp since 
+    // B has multiple return sites.
+    //
+    // Jit will initially type this temp as 'B' but then
+    // sharpen type type to 'B exact' or 'D exact' if the
+    // 'b' is a constant at the call site.
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    static B Choose(bool b)
+    {
+        return b ? new B() : new D();
+    }
+
+    // The calls to F should be devirtualized late
+    public static int Main(string[] args)
+    {
+        int v0 = Choose(false).F(V(67));
+        B b = Choose(true);
+        int v1 = b.F(V(56));
+        return v0 + v1 - 100;
+    }
+}
diff --git a/tests/src/JIT/opt/Devirtualization/late1.csproj b/tests/src/JIT/opt/Devirtualization/late1.csproj
@@ -0,0 +1,38 @@
+<?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	.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="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="late1.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>