[mono][jit] Emit a null check when storing to valuetype fields.

src/mono/mono/mini/ir-emit.h

@@ -882,6 +882,13 @@ static int ccount = 0;
 #define MONO_EMIT_NEW_IMPLICIT_EXCEPTION_LOAD_STORE(cfg) do { \
 	} while (0)
 
+#define MONO_EMIT_EXPLICIT_NULL_CHECK(cfg, reg) do { \
+		cfg->flags |= MONO_CFG_HAS_CHECK_THIS; \
+		MONO_EMIT_NEW_BIALU_IMM (cfg, OP_COMPARE_IMM, -1, (reg), 0);	\
+		MONO_EMIT_NEW_COND_EXC (cfg, EQ, "NullReferenceException");		\
+		MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
+	} while (0)
+
 /* Emit an explicit null check which doesn't depend on SIGSEGV signal handling */
 #define MONO_EMIT_NULL_CHECK(cfg, reg, out_of_page) do { \
 		if (cfg->explicit_null_checks || (out_of_page)) { \

src/mono/mono/mini/method-to-ir.c

@@ -10026,6 +10026,10 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 							EMIT_NEW_BIALU_IMM (cfg, ptr, OP_PADD_IMM, dreg, sp [0]->dreg, foffset);
 							store = mini_emit_storing_write_barrier (cfg, ptr, sp [1]);
 						} else {
+							if (MONO_TYPE_ISSTRUCT (field->type))
+								/* The decomposition might end up calling a copy/wbarrier function which doesn't do null checks */
+								MONO_EMIT_EXPLICIT_NULL_CHECK (cfg, sp [0]->dreg);
+
 							EMIT_NEW_STORE_MEMBASE_TYPE (cfg, store, field->type, sp [0]->dreg, foffset, sp [1]->dreg);
 						}
 					}

src/tests/JIT/Regression/JitBlue/Runtime_82535/Runtime_82535.cs

@@ -0,0 +1,131 @@
+// 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 Program
+{
+	public Program()
+	{
+	}
+
+	static int Main(string[] args)
+	{
+        Foo currentFoo;
+
+		Bacon defaultBacon = new Bacon(-180, 180, true, false, 300f, 0.1f, 0.1f, "Foo", false);
+		currentFoo = new Foo();
+        try {
+            currentFoo.GetBar().m_Bacon = defaultBacon;
+        } catch (NullReferenceException) {
+            return 100;
+        }
+        return 101;
+	}
+}
+
+public class Foo
+{
+	private Bar m_Bar;
+	public Bar GetBar()
+	{
+		return m_Bar;
+	}
+}
+
+
+public class Bar
+{
+	public Bacon m_Bacon = new Bacon(-180, 180, true, false, 300f, 0.1f, 0.1f, "Foo", false);
+}
+
+public struct Bacon
+{
+	public float Value;
+	public enum FooEnum
+	{
+		One,
+		Two
+	};
+
+	public FooEnum m_FooEnum;
+	public float m_f1;
+	public float m_f2;
+	public float m_f3;
+	public string m_s1;
+	public float m_f8;
+	public bool m_bool1;
+	public float m_f4;
+	public float m_f5;
+	public bool m_bool2;
+	public FooBar m_FooBar;
+
+	float m_f6;
+	float m_f7;
+	int m_i1;
+
+	public bool bool3 { get; set; }
+
+	public bool bool4 { get; set; }
+
+	public interface IFooInterface
+	{
+		float GetFooValue(int foo);
+	}
+
+	IFooInterface m_FooProvider;
+	int m_i2;
+
+	public Bacon(
+		float minValue, float maxValue, bool wrap, bool rangeLocked,
+		float maxSpeed, float accelTime, float decelTime,
+		string name, bool invert)
+	{
+		m_f4 = minValue;
+		m_f5 = maxValue;
+		m_bool2 = wrap;
+		bool3 = rangeLocked;
+
+		bool4 = false;
+		m_FooBar = new FooBar(false, 1, 2);
+
+		m_FooEnum = FooEnum.One;
+		m_f1 = maxSpeed;
+		m_f2 = accelTime;
+		m_f3 = decelTime;
+		Value = (minValue + maxValue) / 2;
+		m_s1 = name;
+		m_f8 = 0;
+		m_bool1 = invert;
+
+		m_f6 = 0f;
+		m_FooProvider = null;
+		m_i2 = 0;
+		m_f7 = 0;
+		m_i1 = 0;
+	}
+
+	public struct FooBar
+	{
+		public bool m_FooBar_bool1;
+		public float m_FooBar_f1;
+		public float m_FooBar_f2;
+
+		float m_FooBar_f3;
+		float m_FooBar_f4;
+		float m_FooBar_f5;
+		int m_FooBar_i1;
+		int m_FooBar_i2;
+
+		public FooBar(bool b1, float f1, float f2)
+		{
+			m_FooBar_bool1 = b1;
+			m_FooBar_f1 = f1;
+			m_FooBar_f2 = f2;
+			m_FooBar_f4 = 0;
+			m_FooBar_f5 = 0;
+			m_FooBar_i1 = m_FooBar_i2 = -1;
+			m_FooBar_f3 = 0;
+		}
+	}
+}

src/tests/JIT/Regression/JitBlue/Runtime_82535/Runtime_82535.csproj

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

src/tests/issues.targets

@@ -66,6 +66,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/GC/Regressions/Github/Runtime_76219/Runtime_76219/*">
             <Issue>https://github.com/dotnet/runtime/issues/78899</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_82535/*">
+          <Issue>https://github.com/dotnet/runtime/pull/82663</Issue>
+        </ExcludeList>
     </ItemGroup>
 
     <!-- All Unix targets on all runtimes -->