Fix issue with devirtualization and tailcalls

src/jit/compiler.h

@@ -3329,7 +3329,8 @@ class Compiler
                              unsigned*               methodFlags,
                              CORINFO_CONTEXT_HANDLE* contextHandle,
                              CORINFO_CONTEXT_HANDLE* exactContextHandle,
-                             bool                    isLateDevirtualization);
+                             bool                    isLateDevirtualization,
+                             bool                    isExplicitTailCall);
 
     //=========================================================================
     //                          PROTECTED

src/jit/flowgraph.cpp

@@ -22510,7 +22510,9 @@ Compiler::fgWalkResult Compiler::fgLateDevirtualization(GenTree** pTree, fgWalkD
             unsigned               methodFlags            = 0;
             CORINFO_CONTEXT_HANDLE context                = nullptr;
             const bool             isLateDevirtualization = true;
-            comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr, isLateDevirtualization);
+            bool explicitTailCall = (call->gtCall.gtCallMoreFlags & GTF_CALL_M_EXPLICIT_TAILCALL) != 0;
+            comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr, isLateDevirtualization,
+                                      explicitTailCall);
         }
     }
     else if (tree->OperGet() == GT_ASG)

src/jit/importer.cpp

@@ -5276,7 +5276,7 @@ BOOL Compiler::verIsSDArray(typeInfo ti)
 
 typeInfo Compiler::verGetArrayElemType(typeInfo arrayObjectType)
 {
-    assert(!arrayObjectType.IsNullObjRef()); // you need to check for null explictly since that is a success case
+    assert(!arrayObjectType.IsNullObjRef()); // you need to check for null explicitly since that is a success case
 
     if (!verIsSDArray(arrayObjectType))
     {
@@ -8590,9 +8590,11 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
             assert(obj->gtType == TYP_REF);
 
             // See if we can devirtualize.
+
+            bool       explicitTailCall       = (tailCall & PREFIX_TAILCALL_EXPLICIT) != 0;
             const bool isLateDevirtualization = false;
             impDevirtualizeCall(call->AsCall(), &callInfo->hMethod, &callInfo->methodFlags, &callInfo->contextHandle,
-                                &exactContextHnd, isLateDevirtualization);
+                                &exactContextHnd, isLateDevirtualization, explicitTailCall);
         }
 
         if (impIsThis(obj))
@@ -8742,7 +8744,6 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
 
             if (info.compCompHnd->canTailCall(info.compMethodHnd, methHnd, exactCalleeHnd, explicitTailCall))
             {
-                canTailCall = true;
                 if (explicitTailCall)
                 {
                     // In case of explicit tail calls, mark it so that it is not considered
@@ -20174,6 +20175,7 @@ bool Compiler::IsMathIntrinsic(GenTree* tree)
 //     contextHandle -- [IN/OUT] context handle for the call. Updated iff call devirtualized.
 //     exactContextHnd -- [OUT] updated context handle iff call devirtualized
 //     isLateDevirtualization -- if devirtualization is happening after importation
+//     isExplicitTailCalll -- [IN] true if we plan on using an explicit tail call
 //
 // Notes:
 //     Virtual calls in IL will always "invoke" the base class method.
@@ -20207,7 +20209,8 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
                                    unsigned*               methodFlags,
                                    CORINFO_CONTEXT_HANDLE* contextHandle,
                                    CORINFO_CONTEXT_HANDLE* exactContextHandle,
-                                   bool                    isLateDevirtualization)
+                                   bool                    isLateDevirtualization,
+                                   bool                    isExplicitTailCall)
 {
     assert(call != nullptr);
     assert(method != nullptr);
@@ -20558,6 +20561,12 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
     {
         JITDUMP("Now have direct call to boxed entry point, looking for unboxed entry point\n");
 
+        if (isExplicitTailCall)
+        {
+            JITDUMP("Call is an explicit tail call, we cannot perform an unbox\n");
+            return;
+        }
+
         // Note for some shared methods the unboxed entry point requires an extra parameter.
         bool                  requiresInstMethodTableArg = false;
         CORINFO_METHOD_HANDLE unboxedEntryMethod =
@@ -20640,6 +20649,18 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
                     call->gtCallMethHnd = unboxedEntryMethod;
                     call->gtCallMoreFlags |= GTF_CALL_M_UNBOXED;
                     derivedMethod = unboxedEntryMethod;
+
+#if FEATURE_TAILCALL_OPT
+                    if (call->IsImplicitTailCall())
+                    {
+                        JITDUMP("Clearing the implicit tail call flag\n");
+
+                        // If set, we clear the implicit tail call flag
+                        // as we just introduced a new address taken local variable
+                        //
+                        call->gtCallMoreFlags &= ~GTF_CALL_M_IMPLICIT_TAILCALL;
+                    }
+#endif // FEATURE_TAILCALL_OPT
                 }
                 else
                 {

src/jit/indirectcalltransformer.cpp

@@ -676,14 +676,16 @@ class IndirectCallTransformer
 
             JITDUMP("Direct call [%06u] in block BB%02u\n", compiler->dspTreeID(call), thenBlock->bbNum);
 
-            // Then invoke impDevirtualizeCall do actually
+            // Then invoke impDevirtualizeCall to actually
             // transform the call for us. It should succeed.... as we have
             // now provided an exact typed this.
             CORINFO_METHOD_HANDLE  methodHnd              = inlineInfo->methInfo.ftn;
             unsigned               methodFlags            = inlineInfo->methAttr;
             CORINFO_CONTEXT_HANDLE context                = inlineInfo->exactContextHnd;
             const bool             isLateDevirtualization = true;
-            compiler->impDevirtualizeCall(call, &methodHnd, &methodFlags, &context, nullptr, isLateDevirtualization);
+            bool explicitTailCall = (call->gtCall.gtCallMoreFlags & GTF_CALL_M_EXPLICIT_TAILCALL) != 0;
+            compiler->impDevirtualizeCall(call, &methodHnd, &methodFlags, &context, nullptr, isLateDevirtualization,
+                                          explicitTailCall);
 
             // Presumably devirt might fail? If so we should try and avoid
             // making this a guarded devirt candidate instead of ending

tests/src/JIT/Regression/JitBlue/DevDiv_754566/DevDiv_754566.il

@@ -0,0 +1,106 @@
+// 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.
+
+
+// Metadata version: v4.0.30319
+.assembly extern mscorlib
+{
+  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
+  .ver 4:0:0:0
+}
+.assembly test
+{
+  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 ) 
+  .custom instance void [mscorlib]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78   // ....T..WrapNonEx
+                                                                                                             63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01 )       // ceptionThrows.
+  .hash algorithm 0x00008004
+  .ver 0:0:0:0
+}
+.module test.exe
+// MVID: {A80A87C4-1DDB-4F93-AB31-444266FDFA55}
+.imagebase 0x00400000
+.file alignment 0x00000200
+.stackreserve 0x00100000
+.subsystem 0x0003       // WINDOWS_CUI
+.corflags 0x00000001    //  ILONLY
+// Image base: 0x0000024A58020000
+
+
+// =============== CLASS MEMBERS DECLARATION ===================
+
+.class private auto ansi beforefieldinit Program
+       extends [mscorlib]System.Object
+{
+  .method public hidebysig instance string 
+          Test(int32 val) cil managed noinlining
+  {
+    // This testcase ensures that we don't perform devirtualization
+    // via an unboxing optimization, for the callvirt below.
+
+    // Code size       12 (0xc)
+    .maxstack  8
+    IL_0000:  ldarg.1
+    IL_0001:  box        [mscorlib]System.Int32
+              tail.
+    IL_0006:  callvirt   instance string [mscorlib]System.Object::ToString()
+    IL_000b:  ret
+  } // end of method Program::Test
+
+  .method private hidebysig static int32 
+          Main(string[] args) cil managed
+  {
+    .entrypoint
+    // Code size       73 (0x49)
+    .maxstack  2
+    .locals init (int32 V_0,
+             class Program V_1,
+             string V_2)
+    IL_0000:  ldc.i4.m1
+    IL_0001:  stloc.0
+    IL_0002:  newobj     instance void Program::.ctor()
+    IL_0007:  stloc.1
+    IL_0008:  ldloc.1
+    IL_0009:  ldc.i4.s   42
+    IL_000b:  callvirt   instance string Program::Test(int32)
+    IL_0010:  stloc.2
+    IL_0011:  ldloc.2
+    IL_0012:  ldstr      "42"
+    IL_0017:  call       bool [mscorlib]System.String::op_Equality(string,
+                                                                   string)
+    IL_001c:  brfalse.s  IL_002d
+
+    IL_001e:  ldstr      "=== PASSED ==="
+    IL_0023:  call       void [mscorlib]System.Console::WriteLine(string)
+    IL_0028:  ldc.i4.s   100
+    IL_002a:  stloc.0
+    IL_002b:  br.s       IL_0047
+
+    IL_002d:  ldstr      "result shoudl be 42, is= "
+    IL_0032:  ldloc.2
+    IL_0033:  call       string [mscorlib]System.String::Concat(string,
+                                                                string)
+    IL_0038:  call       void [mscorlib]System.Console::WriteLine(string)
+    IL_003d:  ldstr      "+++ FAILED +++"
+    IL_0042:  call       void [mscorlib]System.Console::WriteLine(string)
+    IL_0047:  ldloc.0
+    IL_0048:  ret
+  } // end of method Program::Main
+
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    // Code size       7 (0x7)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
+    IL_0006:  ret
+  } // end of method Program::.ctor
+
+} // end of class Program
+
+
+// =============================================================
+
+// *********** DISASSEMBLY COMPLETE ***********************
+// WARNING: Created Win32 resource file test2.res

tests/src/JIT/Regression/JitBlue/DevDiv_754566/DevDiv_754566.ilprog

@@ -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 $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <PropertyGroup>
+    <DebugType>PdbOnly</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="DevDiv_754566.il" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>

tests/src/JIT/Regression/JitBlue/DevDiv_754566/test.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Runtime.CompilerServices;
+
+class Program
+{
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public String Test(int val)
+    {
+        return ((Object) val).ToString();
+    }
+
+    static int Main(string[] args)
+    {
+        int exitStatus = -1;
+
+        Program p = new Program();
+
+        String result = p.Test(42);
+	if (result == "42")
+        {
+            Console.WriteLine("=== PASSED ===");
+            exitStatus = 100;
+        }
+        else
+        {
+            Console.WriteLine("result shoudl be 42, is= " + result);
+            Console.WriteLine("+++ FAILED +++");
+        }
+        return exitStatus;
+    }
+}