From 3c712b4edebc46b599319af234484477e5017514 Mon Sep 17 00:00:00 2001
From: Jarret Shook <jashoo@microsoft.com>
Date: Thu, 18 Jul 2019 21:07:08 -0700
Subject: Fail to explicitly tail call on x86 unix. (#25032)

* Fail to explicitly tail call on x86 unix.

* Correctly return 100

* Correct return value

* Add noway assert in morphTailCall to avoid morphing slow tail calls on unix.

* Address feedback
---
 src/jit/morph.cpp                                  |  8 ++++--
 .../JitBlue/GitHub_25020/GitHub_25020.cs           | 32 ++++++++++++++++++++++
 .../JitBlue/GitHub_25020/GitHub_25020.csproj       | 17 ++++++++++++
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.cs
 create mode 100644 tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.csproj

diff --git a/src/jit/morph.cpp b/src/jit/morph.cpp
index c087fb069f..5450b4396c 100644
--- a/src/jit/morph.cpp
+++ b/src/jit/morph.cpp
@@ -7351,6 +7351,10 @@ bool Compiler::fgCanFastTailCall(GenTreeCall* callee)
  */
 void Compiler::fgMorphTailCall(GenTreeCall* call, void* pfnCopyArgs)
 {
+#if defined(_TARGET_UNIX_)
+    noway_assert(!"Slow tail calls not supported on non-Windows platforms.");
+#endif
+
     JITDUMP("fgMorphTailCall (before):\n");
     DISPTREE(call);
 
@@ -8275,7 +8279,7 @@ GenTree* Compiler::fgMorphCall(GenTreeCall* call)
         }
 
         void* pfnCopyArgs = nullptr;
-#if !defined(_TARGET_X86_)
+#if !defined(_TARGET_X86_) || defined(_TARGET_UNIX_)
         if (!canFastTailCall && szFailReason == nullptr)
         {
             pfnCopyArgs =
@@ -8295,7 +8299,7 @@ GenTree* Compiler::fgMorphCall(GenTreeCall* call)
                 }
             }
         }
-#endif // !_TARGET_X86_
+#endif // !defined(_TARGET_X86_) || defined(_TARGET_UNIX_)
 
         if (szFailReason != nullptr)
         {
diff --git a/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.cs b/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.cs
new file mode 100644
index 0000000000..89d54315e8
--- /dev/null
+++ b/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.cs
@@ -0,0 +1,32 @@
+// 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.Reflection;
+using System.Reflection.Emit;
+
+namespace GitHub_25020
+{
+    class Program
+    {    
+        static int Main(string[] args)
+        {
+            DynamicMethod dm = new DynamicMethod("MyMethod", typeof(string), new Type[] { typeof(string), typeof(string) });
+            
+            ILGenerator generator = dm.GetILGenerator();
+            generator.Emit(OpCodes.Ldarg_0);
+            generator.Emit(OpCodes.Ldarg_1);
+            generator.Emit(OpCodes.Tailcall);
+            generator.EmitCall(OpCodes.Call, typeof(String).GetMethod("Concat", new Type[] { typeof(string), typeof(string) }), null);
+            generator.Emit(OpCodes.Ret);
+
+            string a = "1234";
+            string b = "abcd";
+            
+            Console.WriteLine(dm.Invoke(null, BindingFlags.Default, null, new object[] {a, b}, null));
+
+            return 100;
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.csproj b/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.csproj
new file mode 100644
index 0000000000..c24f74b865
--- /dev/null
+++ b/tests/src/JIT/Regression/JitBlue/GitHub_25020/GitHub_25020.csproj
@@ -0,0 +1,17 @@
+<?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=" '$(Configuration)' == '' ">Release</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <AssemblyName>$(MSBuildProjectName)</AssemblyName>
+    <OutputType>Exe</OutputType>
+    <DebugType></DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>
-- 
cgit v1.2.3