JIT: fix OSR handling for pinned locals

src/coreclr/jit/lclvars.cpp

@@ -289,6 +289,14 @@ void Compiler::lvaInitTypeRef()
             {
                 JITDUMP("Setting lvPinned for V%02u\n", varNum);
                 varDsc->lvPinned = 1;
+
+                if (opts.IsOSR())
+                {
+                    // OSR method may not see any references to the pinned local,
+                    // but must still report it in GC info.
+                    //
+                    varDsc->lvImplicitlyReferenced = 1;
+                }
             }
             else
             {

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

@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+// Run under COMPlus_GCStress=3
+
+class PinnedLocal
+{
+    static int F(char c)
+    {
+        return (int) c;
+    }
+
+    public static unsafe int Main()
+    {
+        string ss = "goodbye, world\n";
+        string s = "hello, world\n";
+        int r = 0;
+        fixed(char* p = s)
+        {
+            for (int i = 0; i < 100_000; i++)
+            {
+                r += F(p[i % s.Length]);
+
+                if ((i % 10_000) == 0)
+                {
+                    GC.Collect(2);
+                    ss = new String('a', 100);
+                }
+            }
+
+            Console.WriteLine($"r is {r}");
+            return r - 9000061 + 100;
+        }
+    }
+}

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

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <DebugType />
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <PropertyGroup>
+    <CLRTestBatchPreCommands><![CDATA[
+$(CLRTestBatchPreCommands)
+set COMPlus_GCStress=3
+]]></CLRTestBatchPreCommands>
+    <BashCLRTestPreCommands><![CDATA[
+$(BashCLRTestPreCommands)
+export COMPlus_GCStress=3
+]]></BashCLRTestPreCommands>
+  </PropertyGroup>
+</Project>