From 0ef205d30e893ff3af0dce4933606871cfdd994c Mon Sep 17 00:00:00 2001
From: SingleAccretion <62474226+SingleAccretion@users.noreply.github.com>
Date: Tue, 4 Jan 2022 00:03:55 +0300
Subject: [PATCH] Do not create non-null assertions from location nodes
 (#62743)

---
 src/coreclr/jit/assertionprop.cpp                  | 26 ++++++++++++---
 .../JitBlue/Runtime_13762/Runtime_13762.cs         | 39 ++++++++++++++++++++++
 .../JitBlue/Runtime_13762/Runtime_13762.csproj     |  9 +++++
 3 files changed, 69 insertions(+), 5 deletions(-)
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.cs
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.csproj

diff --git a/src/coreclr/jit/assertionprop.cpp b/src/coreclr/jit/assertionprop.cpp
index b842e13..71d2dc6 100644
--- a/src/coreclr/jit/assertionprop.cpp
+++ b/src/coreclr/jit/assertionprop.cpp
@@ -2558,8 +2558,14 @@ void Compiler::optAssertionGen(GenTree* tree)
     switch (tree->gtOper)
     {
         case GT_ASG:
+            // An indirect store - we can create a non-null assertion. Note that we do not lose out
+            // on the dataflow assertions here as local propagation only deals with LCL_VAR LHSs.
+            if (tree->AsOp()->gtGetOp1()->OperIsIndir())
+            {
+                assertionInfo = optCreateAssertion(tree->AsOp()->gtGetOp1()->AsIndir()->Addr(), nullptr, OAK_NOT_EQUAL);
+            }
             // VN takes care of non local assertions for assignments and data flow.
-            if (optLocalAssertionProp)
+            else if (optLocalAssertionProp)
             {
                 assertionInfo = optCreateAssertion(tree->AsOp()->gtOp1, tree->AsOp()->gtOp2, OAK_EQUAL);
             }
@@ -2573,16 +2579,26 @@ void Compiler::optAssertionGen(GenTree* tree)
         case GT_BLK:
         case GT_DYN_BLK:
         case GT_IND:
-        case GT_NULLCHECK:
-            // All indirections create non-null assertions
-            assertionInfo = optCreateAssertion(tree->AsIndir()->Addr(), nullptr, OAK_NOT_EQUAL);
+            // R-value indirections create non-null assertions, but not all indirections are R-values.
+            // Those under ADDR nodes or on the LHS of ASGs are "locations", and will not end up
+            // dereferencing their operands. We cannot reliably detect them here, however, and so
+            // will have to rely on the conservative approximation of the GTF_NO_CSE flag.
+            if (tree->CanCSE())
+            {
+                assertionInfo = optCreateAssertion(tree->AsIndir()->Addr(), nullptr, OAK_NOT_EQUAL);
+            }
             break;
 
         case GT_ARR_LENGTH:
-            // An array length is an indirection (but doesn't derive from GenTreeIndir).
+            // An array length is an (always R-value) indirection (but doesn't derive from GenTreeIndir).
             assertionInfo = optCreateAssertion(tree->AsArrLen()->ArrRef(), nullptr, OAK_NOT_EQUAL);
             break;
 
+        case GT_NULLCHECK:
+            // Explicit null checks always create non-null assertions.
+            assertionInfo = optCreateAssertion(tree->AsIndir()->Addr(), nullptr, OAK_NOT_EQUAL);
+            break;
+
         case GT_BOUNDS_CHECK:
             if (!optLocalAssertionProp)
             {
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.cs b/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.cs
new file mode 100644
index 0000000..f02a9af
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.cs
@@ -0,0 +1,39 @@
+// 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;
+
+public class Runtime_13762
+{
+    public static int Main()
+    {
+        try
+        {
+            Problem(null);
+        }
+        catch (NullReferenceException)
+        {
+            return 100;
+        }
+
+        return 101;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Problem(ClassWithField a)
+    {
+        a.Field = a.Call(ref a.Field);
+    }
+}
+
+public class ClassWithField
+{
+    public int Field;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public int Call(ref int a)
+    {
+        throw new Exception("This should have been an NRE!");
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.csproj
new file mode 100644
index 0000000..f492aea
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_13762/Runtime_13762.csproj
@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
-- 
2.7.4