From 7a7b626bd3ff2e8c12752bec0650082a82a32f1c Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Wed, 8 Apr 2026 15:56:49 +0200
Subject: [PATCH] JIT: Handle writes to promoted locals in `AliasSet::AddNode`

---
 src/coreclr/jit/sideeffects.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/coreclr/jit/sideeffects.cpp b/src/coreclr/jit/sideeffects.cpp
index 5b642529c62f57..8c640633921fb0 100644
--- a/src/coreclr/jit/sideeffects.cpp
+++ b/src/coreclr/jit/sideeffects.cpp
@@ -318,6 +318,19 @@ void AliasSet::AddNode(Compiler* compiler, GenTree* node)
     if (nodeInfo.IsLclVarWrite())
     {
         m_lclVarWrites.Add(compiler, nodeInfo.LclNum());
+
+        LclVarDsc* dsc = compiler->lvaGetDesc(nodeInfo.LclNum());
+        if (dsc->lvIsStructField)
+        {
+            m_lclVarWrites.Add(compiler, dsc->lvParentLcl);
+        }
+        else if (dsc->lvPromoted)
+        {
+            for (unsigned i = 0; i < dsc->lvFieldCnt; i++)
+            {
+                m_lclVarWrites.Add(compiler, dsc->lvFieldLclStart + i);
+            }
+        }
     }
 }