JIT: Mark replacements as dirty after setting GTF_VAR_DEATH

src/coreclr/jit/promotion.cpp

@@ -2404,6 +2404,14 @@ void ReplaceVisitor::ReplaceLocal(GenTree** use, GenTree* user)
         {
             lcl->gtFlags |= GTF_VAR_DEATH;
             CheckForwardSubForLastUse(lclNum);
+
+            // Relying on the values in the struct local after this struct use
+            // would effectively introduce another use of the struct, so
+            // indicate that no replacements are up to date.
+            for (Replacement& rep : replacements)
+            {
+                SetNeedsWriteBack(rep);
+            }
         }
         return;
     }

src/tests/JIT/Regression/JitBlue/Runtime_88616/Runtime_88616.cs

@@ -0,0 +1,63 @@
+// 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_88616
+{
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        S foo;
+        foo.A = 10;
+        foo.B = 20;
+        foo.C = 30;
+        foo.D = 40;
+        foo.E = 50;
+        foo.A += foo.A += foo.A += foo.A += foo.A;
+        foo.B += foo.B += foo.B += foo.B += foo.B;
+        foo.C += foo.C += foo.C += foo.C += foo.C;
+        foo.D += foo.D += foo.D += foo.D += foo.D;
+        foo.E += foo.E += foo.E += foo.E += foo.E;
+        // 'foo' is a last use here (it is fully promoted so all of its state
+        // is stored in separate field locals), so physical promotions marks
+        // this occurence as GTF_VAR_DEATH.
+        Mutate(foo);
+        // However, we cannot use the fact that we wrote the fields back into
+        // the struct local above to skip those same write backs here; if we
+        // skip those write backs then we effectively introduce new uses of the
+        // struct local.
+        return Check(foo);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Mutate(S s)
+    {
+        s.A = -42;
+        Consume(ref s);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Consume(ref S s)
+    {
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static int Check(S s)
+    {
+        if (s.A != 50)
+        {
+            Console.WriteLine("FAIL: s.A == {0}", s.A);
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private struct S
+    {
+        public long A, B, C, D, E;
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_88616/Runtime_88616.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+    <DebugType>None</DebugType>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>