JIT: fix interaction of OSR and shadowed parameters

src/coreclr/jit/compiler.cpp

@@ -5244,7 +5244,23 @@ void Compiler::generatePatchpointInfo()
     // but would need to adjust all consumers, too.
     for (unsigned lclNum = 0; lclNum < info.compLocalsCount; lclNum++)
     {
-        LclVarDsc* const varDsc = lvaGetDesc(lclNum);
+        // If there are shadowed params, the patchpoint info should refer to the shadow copy.
+        //
+        unsigned varNum = lclNum;
+
+        if (gsShadowVarInfo != nullptr)
+        {
+            unsigned const shadowNum = gsShadowVarInfo[lclNum].shadowCopy;
+            if (shadowNum != BAD_VAR_NUM)
+            {
+                assert(shadowNum < lvaCount);
+                assert(shadowNum >= info.compLocalsCount);
+
+                varNum = shadowNum;
+            }
+        }
+
+        LclVarDsc* const varDsc = lvaGetDesc(varNum);
 
         // We expect all these to have stack homes, and be FP relative
         assert(varDsc->lvOnFrame);
@@ -5260,8 +5276,8 @@ void Compiler::generatePatchpointInfo()
             patchpointInfo->SetIsExposed(lclNum);
         }
 
-        JITDUMP("--OSR-- V%02u is at virtual offset %d%s\n", lclNum, patchpointInfo->Offset(lclNum),
-                patchpointInfo->IsExposed(lclNum) ? " (exposed)" : "");
+        JITDUMP("--OSR-- V%02u is at virtual offset %d%s%s\n", lclNum, patchpointInfo->Offset(lclNum),
+                patchpointInfo->IsExposed(lclNum) ? " (exposed)" : "", (varNum != lclNum) ? " (shadowed)" : "");
     }
 
     // Special offsets

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

@@ -0,0 +1,44 @@
+// 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;
+
+// F is an OSR method with parameter shadowing
+
+public unsafe struct ShadowParam
+{
+    public int a;
+    public fixed int data[2];
+    public int b;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static int F(int x, string sa, ShadowParam u, string sb, int a, int b, int y)
+    {
+        for (int i = 0; i < a + b; i++)
+        {
+            x += u.data[0];
+        }
+
+        for (int i = 0; i < a + b; i++)
+        {
+            y += u.data[1];
+        }
+
+        return x + y + u.a + u.b + sb.Length - sa.Length;
+    }
+
+    public static int Main()
+    {
+        var u = new ShadowParam();
+        u.data[0] = 1;
+        u.data[1] = -1;
+        u.a = 3;
+        u.b = -3;
+
+        int r = F(0, "a", u, "b", 100_001, -1, 100);
+        Console.WriteLine($"Result is {r}");
+        return r;
+    }
+}
+

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

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <DebugType />
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>