From e4cb4dd894472a9c5efef31e588a9caefd635d24 Mon Sep 17 00:00:00 2001
From: Joseph Tremoulet <jotrem@microsoft.com>
Date: Mon, 22 Aug 2016 21:14:24 -0400
Subject: [PATCH] Fix IMGREL32 static field addr value-num blindspot

When `fgMorphField` lowers a static field reference for which
`eeGetRelocTypeHint` returns `IMAGE_REL_BASED_REL32`, it creates an
`IntCon`, flagged with `GFT_ICON_STATIC_HDL` and marked with the static
field in its `gtFieldSeq` field, to represent the field's address (as
opposed to the normal case where it generates a `ClsVar`).  This change
updates the `IsFieldAddr` helper used by value-numbering/loop-hoisting to
recognize such constants as the appropriate field address, which then
allows the disambiguation/tracking of accesses to these fields to kick in
as it does for `ClsVar` nodes.

Also update test GC/Scenarios/FinalizeTimeout to mark a bool volatile that
otherwise can get hoisted (the test aims to observe finalization from a
side-effect-free busy-loop by communicating through this bool).

Fixes #6900.
---
 src/jit/gentree.cpp                           | 26 +++++++++++--------
 .../FinalizeTimeout/FinalizeTimeout.cs        |  2 +-
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/jit/gentree.cpp b/src/jit/gentree.cpp
index 01c383a7f908..63603d8b0ff5 100644
--- a/src/jit/gentree.cpp
+++ b/src/jit/gentree.cpp
@@ -15275,19 +15275,23 @@ bool GenTree::IsFieldAddr(Compiler* comp, GenTreePtr* pObj, GenTreePtr* pStatic,
             baseAddr  = gtOp.gtOp1;
         }
     }
+    // Check if "this" has a zero-offset annotation.
+    else if (comp->GetZeroOffsetFieldMap()->Lookup(this, &newFldSeq))
+    {
+        baseAddr = this;
+        mustBeStatic = true;
+    }
+    else if (OperGet() == GT_CNS_INT && gtIntCon.gtFieldSeq != nullptr)
+    {
+        // Address is a literal constant; must be a static field.
+        newFldSeq = gtIntCon.gtFieldSeq;
+        baseAddr = this;
+        mustBeStatic = true;
+    }
     else
     {
-        // Check if "this" has a zero-offset annotation.
-        if (!comp->GetZeroOffsetFieldMap()->Lookup(this, &newFldSeq))
-        {
-            // If not, this is not a field address.
-            return false;
-        }
-        else
-        {
-            baseAddr     = this;
-            mustBeStatic = true;
-        }
+        // This is not a field address.
+        return false;
     }
 
     // If not we don't have a field seq, it's not a field address.
diff --git a/tests/src/GC/Scenarios/FinalizeTimeout/FinalizeTimeout.cs b/tests/src/GC/Scenarios/FinalizeTimeout/FinalizeTimeout.cs
index 0fda8172e49f..0935b4524f7f 100644
--- a/tests/src/GC/Scenarios/FinalizeTimeout/FinalizeTimeout.cs
+++ b/tests/src/GC/Scenarios/FinalizeTimeout/FinalizeTimeout.cs
@@ -47,7 +47,7 @@ private static void ThreadMain()
 
     private class BlockingFinalizerOnShutdown
     {
-        public static bool finalizerCompletedOnce = false;
+        public volatile static bool finalizerCompletedOnce = false;
         public bool isLastObject = false;
 
         ~BlockingFinalizerOnShutdown()