From b875090d05551cebc97214f72140921fc7f6d50d Mon Sep 17 00:00:00 2001
From: Andreas Pardeike <andreas@pardeike.net>
Date: Tue, 17 Jan 2017 00:47:20 +0100
Subject: [PATCH] Improved memory method so JIT compiler does not optimize it
 away

---
 Harmony/Harmony.csproj | 12 +-----------
 Harmony/Platform.cs    | 27 +++++++++++++++++----------
 2 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/Harmony/Harmony.csproj b/Harmony/Harmony.csproj
index 638fe1b3..215e84d1 100644
--- a/Harmony/Harmony.csproj
+++ b/Harmony/Harmony.csproj
@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
@@ -62,16 +62,6 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Traverse.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System" />
-    <Reference Include="System.Core">
-      <Private>False</Private>
-    </Reference>
-    <Reference Include="System.Xml" />
-    <Reference Include="System.Xml.Linq">
-      <Private>False</Private>
-    </Reference>
-  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <PropertyGroup>
     <PostBuildEvent>if exist "$(TargetDir)$(TargetName).pdb" "C:\Program Files (x86)\Mono\bin\mono.exe" "C:\Program Files (x86)\Mono\lib\mono\4.5\pdb2mdb.exe" "$(TargetPath)"</PostBuildEvent>
diff --git a/Harmony/Platform.cs b/Harmony/Platform.cs
index 8e3d6d27..eee6e8bd 100644
--- a/Harmony/Platform.cs
+++ b/Harmony/Platform.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Reflection;
 using System.Reflection.Emit;
+using System.Runtime.InteropServices;
 
 namespace Harmony
 {
@@ -99,6 +100,18 @@ public static unsafe long WriteLong(long memory, long value)
 			return memory + sizeof(long);
 		}
 
+		// purpose of this method is to "do some work" so the JIT compiler
+		// does not optimize our code away. since it is never called with 0
+		// it actually does nothing
+		public static void LongConsumer(long val)
+		{
+			if (val == 0) Console.WriteLine(val);
+		}
+
+		// the way we create rwx memory is by building a new method and making
+		// sure the JIT compiler does not optimize our code away. We force this
+		// by calling a second method. the loop runs an estimated times to make
+		// sure we have enough assembler code to cover our memory size
 		static int counter;
 		public static long GetMemory(int size)
 		{
@@ -110,21 +123,15 @@ public static long GetMemory(int size)
 			var methodName = "HarmonyMemoryMethod" + counter;
 			var methodBuilder = typeBuilder.DefineMethod(methodName, MethodAttributes.Public | MethodAttributes.Static, typeof(void), new Type[0]);
 			var il = methodBuilder.GetILGenerator();
-			// lets try to be clever enough that no optimization reduces our JIT code size
-			il.DeclareLocal(typeof(int));
-			il.Emit(OpCodes.Ldc_I4, 0);
-			for (int i = 1; i <= size / 2; i++) // size/2 is a rough estimate
+			for (var i = 1; i <= 1 + (size / 8); i++)
 			{
-				il.Emit(OpCodes.Stloc_0);
-				il.Emit(OpCodes.Ldloc_0);
-				il.Emit(OpCodes.Ldc_I4, i);
-				il.Emit(OpCodes.Add);
+				il.Emit(OpCodes.Ldc_I8, 0x1000000000000000 + i);
+				il.Emit(OpCodes.Call, typeof(Platform).GetMethod("LongConsumer"));
 			}
-			il.Emit(OpCodes.Stloc_0);
 			il.Emit(OpCodes.Ret);
 			var type = typeBuilder.CreateType();
 			var m = type.GetMethod(methodName);
-			m.Invoke(null, new object[] { });
+			m.Invoke(null, new object[] { }); // make sure it is JIT-compiled
 			return m.MethodHandle.GetFunctionPointer().ToInt64();
 		}
 	}