JIT: block some struct promotion for OSR

src/coreclr/jit/lclvars.cpp

@@ -1851,6 +1851,14 @@ bool Compiler::StructPromotionHelper::CanPromoteStructVar(unsigned lclNum)
         return false;
     }
 
+    // If the local was exposed at Tier0, we currently have to assume it's aliased for OSR.
+    //
+    if (compiler->lvaIsOSRLocal(lclNum) && compiler->info.compPatchpointInfo->IsExposed(lclNum))
+    {
+        JITDUMP("  struct promotion of V%02u is disabled because it is an exposed OSR local\n", lclNum);
+        return false;
+    }
+
     CORINFO_CLASS_HANDLE typeHnd = varDsc->GetStructHnd();
     assert(typeHnd != NO_CLASS_HANDLE);
 

src/tests/JIT/opt/OSR/invalidpromotion.cs

@@ -0,0 +1,73 @@
+// 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;
+
+interface IFoo 
+{
+    public Span<object> AsSpan();
+}
+
+public struct ObjectSequence1 : IFoo
+{
+    public object Value1;
+
+    public Span<object> AsSpan()
+    {
+        return MemoryMarshal.CreateSpan(ref Value1, 1);
+    }
+}
+
+public struct ObjectSequenceMany : IFoo
+{
+    public object[] _values;
+
+    public Span<object> AsSpan()
+    {
+        return _values.AsSpan();
+    }
+
+    public ObjectSequenceMany(object[] x)
+    {
+        _values = x;
+    }
+}
+
+public class InvalidPromotion
+{
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static bool G<T>(int n) where T : IFoo
+    {
+        // OSR cannot safely promote values
+        T values = default;
+
+        if (values is ObjectSequenceMany)
+        {
+            values = (T)(object)new ObjectSequenceMany(new object[5]);
+        }
+
+        Span<object> indexedValues = values.AsSpan();
+
+        // For a patchpoint here.
+        for (int i = 0; i < n; i++)
+        {
+            indexedValues[i] = "foo";
+        }
+
+        if (values is ObjectSequence1)
+        {
+            return (indexedValues[0] == ((ObjectSequence1)(object)values).Value1);
+        }
+
+        return false;
+    }
+
+    public static int Main()
+    {
+        return G<ObjectSequence1>(1) ? 100 : -1;
+    }
+}
+
+

src/tests/JIT/opt/OSR/invalidpromotion.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <DebugType />
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <PropertyGroup>
+    <CLRTestBatchPreCommands><![CDATA[
+$(CLRTestBatchPreCommands)
+set COMPlus_TieredCompilation=1
+set COMPlus_TC_QuickJitForLoops=1
+set COMPlus_TC_OnStackReplacement=1
+set COMPlus_OSR_HitLimit=1
+set COMPlus_TC_OnStackReplacement=1
+set COMPlus_TC_OnStackReplacement_InitialCounter=1
+]]></CLRTestBatchPreCommands>
+    <BashCLRTestPreCommands><![CDATA[
+$(BashCLRTestPreCommands)
+export COMPlus_TieredCompilation=1
+export COMPlus_TC_QuickJitForLoops=1
+export COMPlus_TC_OnStackReplacement=1
+export COMPlus_OSR_HitLimit=1
+export COMPlus_TC_OnStackReplacement=1
+export COMPlus_TC_OnStackReplacement_InitialCounter=1
+]]></BashCLRTestPreCommands>
+  </PropertyGroup>
+</Project>