Fix JIT using too wide indirections when returning small structs

src/coreclr/jit/lower.cpp

@@ -3644,15 +3644,15 @@ void Lowering::LowerRetStruct(GenTreeUnOp* ret)
     assert(ret->OperIs(GT_RETURN));
     assert(varTypeIsStruct(ret));
 
-    GenTree* retVal = ret->gtGetOp1();
+    GenTree*  retVal           = ret->gtGetOp1();
+    var_types nativeReturnType = comp->info.compRetNativeType;
     // Note: small types are returned as INT.
-    var_types nativeReturnType = genActualType(comp->info.compRetNativeType);
-    ret->ChangeType(nativeReturnType);
+    ret->ChangeType(genActualType(nativeReturnType));
 
     switch (retVal->OperGet())
     {
         case GT_CALL:
-            assert(retVal->TypeIs(nativeReturnType)); // Type should be changed during call processing.
+            assert(retVal->TypeIs(genActualType(nativeReturnType))); // Type should be changed during call processing.
             break;
 
         case GT_CNS_INT:

src/tests/JIT/Regression/JitBlue/Runtime_58874/Runtime_58874.cs

@@ -0,0 +1,97 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+public unsafe class Runtime_58874
+{
+    private static int Main(string[] args)
+    {
+        using EndOfPage endOfPage = EndOfPage.Create();
+        if (endOfPage != null)
+        {
+            Foo(endOfPage.Pointer);
+        }
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static Test Foo(Test* t)
+    {
+        // This read was too wide.
+        return *t;
+    }
+
+    private class EndOfPage : IDisposable
+    {
+        private void* _addr;
+        private EndOfPage()
+        {
+        }
+
+        public Test* Pointer => (Test*)((byte*)_addr + 0x1000 - sizeof(Test));
+        public void Dispose()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                const int MEM_RELEASE = 0x8000;
+                VirtualFree(_addr, 0, MEM_RELEASE);
+            }
+            else
+            {
+                NativeMemory.Free(_addr);
+            }
+        }
+
+        public static EndOfPage Create()
+        {
+            void* mem;
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                const int MEM_COMMIT = 0x1000;
+                const int MEM_RESERVE = 0x2000;
+                const int PAGE_READWRITE = 0x04;
+
+                // Reserve 2 pages
+                void* pages = VirtualAlloc(null, 0x2000, MEM_RESERVE, PAGE_READWRITE);
+                if (pages == null)
+                {
+                    return null;
+                }
+                // Commit first page
+                mem = VirtualAlloc(pages, 0x1000, MEM_COMMIT, PAGE_READWRITE);
+                if (mem != pages)
+                {
+                    return null;
+                }
+            }
+            else
+            {
+                try
+                {
+                    mem = NativeMemory.Alloc(0x1000);
+                }
+                catch (OutOfMemoryException)
+                {
+                    return null;
+                }
+            }
+
+            return new EndOfPage { _addr = mem };
+        }
+
+        [DllImport("kernel32")]
+        private static extern void* VirtualAlloc(void* lpAddress, nuint dwSize, uint flAllocationType, uint flProtect);
+
+        [DllImport("kernel32")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        private static extern bool VirtualFree(void* lpAddress, nuint dwSize, uint dwFreeType);
+    }
+}
+
+struct Test
+{
+    public byte A, B;
+}

src/tests/JIT/Regression/JitBlue/Runtime_58874/Runtime_58874.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>