From 6c1687247482acca944b56c47fc78b6a590962b8 Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Sat, 11 Sep 2021 11:07:13 +0200
Subject: [PATCH 1/2] Remove benign assert

It is perfectly possible for us to replace a promoted struct by its only
field where that field is marked do-not-enregister. Since this path does
handle the proper retyping when normalization is required this assertion
is benign.

Fix #58972
---
 src/coreclr/jit/lower.cpp                     |  1 -
 .../JitBlue/Runtime_58972/Runtime_58972_1.cs  | 37 +++++++++++++++++++
 .../Runtime_58972/Runtime_58972_1.csproj      | 12 ++++++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj

diff --git a/src/coreclr/jit/lower.cpp b/src/coreclr/jit/lower.cpp
index b8752042b1c72f..46137c227399d2 100644
--- a/src/coreclr/jit/lower.cpp
+++ b/src/coreclr/jit/lower.cpp
@@ -3433,7 +3433,6 @@ void Lowering::LowerRetSingleRegStructLclVar(GenTreeUnOp* ret)
 
     if (varDsc->lvDoNotEnregister)
     {
-        assert(!replacedInLowering);
         lclVar->ChangeOper(GT_LCL_FLD);
         lclVar->AsLclFld()->SetLclOffs(0);
 
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs
new file mode 100644
index 00000000000000..c4abdc70b32b1c
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs
@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+public class Runtime_58972
+{
+    public static unsafe int Main()
+    {
+        GetItem(new MyStruct[1], 0);
+        return 100;
+    }
+
+	// This code results in a struct returned in register where we replace the local
+	// of type MyStruct by its only field, and where that field cannot be enregistered.
+	// We would potentially miss normalization if the struct was returned as an integer
+	// type and hit a defensive assertion because of it.
+    static MyStruct GetItem(MyStruct[] a, int i)
+    {
+        try
+        {
+            return a[i];
+        }
+        catch (IndexOutOfRangeException)
+        {
+            ThrowHelper();
+            return default;
+        }
+    }
+
+    static void ThrowHelper() => throw new Exception();
+
+    struct MyStruct
+    {
+        byte b;
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj
new file mode 100644
index 00000000000000..f3e1cbd44b4041
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>

From a073b2c4f7efd2b1cd7c132e713765830c1e332a Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Sat, 11 Sep 2021 21:59:11 +0200
Subject: [PATCH 2/2] Fix test

---
 .../Runtime_58972/{Runtime_58972_1.cs => Runtime_58972.cs}      | 2 +-
 .../{Runtime_58972_1.csproj => Runtime_58972.csproj}            | 0
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename src/tests/JIT/Regression/JitBlue/Runtime_58972/{Runtime_58972_1.cs => Runtime_58972.cs} (96%)
 rename src/tests/JIT/Regression/JitBlue/Runtime_58972/{Runtime_58972_1.csproj => Runtime_58972.csproj} (100%)

diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972.cs
similarity index 96%
rename from src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs
rename to src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972.cs
index c4abdc70b32b1c..b63c1d907f14c1 100644
--- a/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.cs
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972.cs
@@ -5,7 +5,7 @@
 
 public class Runtime_58972
 {
-    public static unsafe int Main()
+    public static int Main()
     {
         GetItem(new MyStruct[1], 0);
         return 100;
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972.csproj
similarity index 100%
rename from src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972_1.csproj
rename to src/tests/JIT/Regression/JitBlue/Runtime_58972/Runtime_58972.csproj