JIT: Fix codegen for misaligned double STORE_LCL_FLD on arm32 (#109547

)

src/coreclr/jit/codegenarm.cpp

@@ -1036,7 +1036,7 @@ void CodeGen::genCodeForStoreLclFld(GenTreeLclFld* tree)
             regNumber halfdoubleAsInt2 = internalRegisters.GetSingle(tree);
             emit->emitIns_R_R_R(INS_vmov_d2i, EA_8BYTE, halfdoubleAsInt1, halfdoubleAsInt2, dataReg);
             emit->emitIns_R_R_I(INS_str, EA_4BYTE, halfdoubleAsInt1, addr, 0);
-            emit->emitIns_R_R_I(INS_str, EA_4BYTE, halfdoubleAsInt1, addr, 4);
+            emit->emitIns_R_R_I(INS_str, EA_4BYTE, halfdoubleAsInt2, addr, 4);
         }
     }
     else

src/tests/JIT/Regression/JitBlue/Runtime_109269/Runtime_109269.cs

@@ -0,0 +1,28 @@
+// 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;
+using Xunit;
+
+public class Runtime_108969
+{
+    [Fact]
+    public static int TestEntryPoint() => (int)Foo(100.0).D;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static S Foo(double d)
+    {
+        S s = default;
+        s.D = d;
+        return s;
+    }
+
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    struct S
+    {
+        public byte B;
+        public double D;
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_109269/Runtime_109269.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <!-- Needed for CLRTestEnvironmentVariable -->
+    <RequiresProcessIsolation>true</RequiresProcessIsolation>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <CLRTestEnvironmentVariable Include="DOTNET_JitNoStructPromotion" Value="1" />
+  </ItemGroup>
+</Project>