[NativeAOT] Add null checks into memcpy/memset helpers (#98547)

Author: filipnavara

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerHelpers/MemoryHelpers.cs

@@ -0,0 +1,33 @@
+// 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;
+
+namespace Internal.Runtime.CompilerHelpers
+{
+    /// <summary>
+    /// These methods are used to implement memcpy and memset intrinsics with null checks.
+    /// </summary>
+    internal static class MemoryHelpers
+    {
+        private static unsafe void MemSet(ref byte dest, byte value, nuint size)
+        {
+            if (size > 0)
+            {
+                _ = dest;
+                SpanHelpers.Fill(ref dest, size, value);
+            }
+        }
+
+        private static unsafe void MemCopy(ref byte dest, ref byte src, nuint size)
+        {
+            if (size > 0)
+            {
+                _ = dest;
+                _ = src;
+                Buffer.Memmove(ref dest, ref src, size);
+            }
+        }
+    }
+}

src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj

@@ -100,6 +100,7 @@
     <Compile Include="Internal\Runtime\CompilerHelpers\ArrayHelpers.cs" />
     <Compile Include="Internal\Runtime\CompilerHelpers\InteropHelpers.cs" />
     <Compile Include="Internal\Runtime\CompilerHelpers\LdTokenHelpers.cs" />
+    <Compile Include="Internal\Runtime\CompilerHelpers\MemoryHelpers.cs" />
     <Compile Include="Internal\Runtime\CompilerHelpers\RuntimeInteropData.cs" />
     <Compile Include="Internal\Runtime\CompilerHelpers\SynchronizedMethodHelpers.cs" />
     <Compile Include="Internal\Runtime\CompilerHelpers\TypedReferenceHelpers.cs" />

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/JitHelper.cs

@@ -134,10 +134,10 @@ public static void GetEntryPoint(TypeSystemContext context, ReadyToRunHelper id,
                     break;
 
                 case ReadyToRunHelper.MemCpy:
-                    mangledName = "memcpy"; // TODO: Null reference handling
+                    methodDesc = context.GetHelperEntryPoint("MemoryHelpers", "MemCopy");
                     break;
                 case ReadyToRunHelper.MemSet:
-                    mangledName = "memset"; // TODO: Null reference handling
+                    methodDesc = context.GetHelperEntryPoint("MemoryHelpers", "MemSet");
                     break;
 
                 case ReadyToRunHelper.GetRuntimeTypeHandle: