Fix SelectLocalIndirTransform to take offset into account (#88951)

Author: EgorBo

src/coreclr/jit/lclmorph.cpp

@@ -1133,7 +1133,7 @@ class LocalAddressVisitor final : public GenTreeVisitor<LocalAddressVisitor>
             }
 #endif // FEATURE_HW_INTRINSICS
 
-            if (!isDef)
+            if ((!isDef) && (offset == 0))
             {
                 if (varTypeIsIntegral(indir) && varTypeIsIntegral(varDsc))
                 {

src/tests/JIT/Regression/JitBlue/Runtime_88950/Runtime_88950.cs

@@ -0,0 +1,70 @@
+// 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 Xunit;
+
+public class Runtime_88950
+{
+    internal readonly struct Example
+    {
+        public readonly object? Value;
+        public readonly ulong Inner;
+
+        struct ExampleInner
+        {
+            public int Offset;
+            public int Length;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Example(object? value, int offset, int length)
+        {
+            var inner = new ExampleInner
+            {
+                Offset = offset,
+                Length = length
+            };
+
+            Value = value;
+            Inner = Unsafe.As<ExampleInner, ulong>(ref inner);
+        }
+        public int Offset
+        {
+            [MethodImpl(MethodImplOptions.AggressiveOptimization | MethodImplOptions.NoInlining)]
+            get
+            {
+                var inner = Inner;
+                return Unsafe.As<ulong, ExampleInner>(ref inner).Offset;
+            }
+        }
+
+        public int Length
+        {
+            [MethodImpl(MethodImplOptions.AggressiveOptimization | MethodImplOptions.NoInlining)]
+            get
+            {
+                ulong inner = Inner;
+                return Unsafe.As<ulong, ExampleInner>(ref inner).Length;
+            }
+        }
+    }
+
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        var repro = new Example(new object(), 1234, 5678);
+        if (repro.Offset != 1234)
+        {
+            Console.WriteLine($"Offset: {repro.Offset}");
+            return 1;
+        }
+        if (repro.Length != 5678)
+        {
+            Console.WriteLine($"Length: {repro.Length}");
+            return 2;
+        }
+        return 100;
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_88950/Runtime_88950.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>