Use `nint` type for local IntPtr variables if arithmetic is performed on them.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NativeInts.cs

@@ -161,5 +161,38 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 			GetInstance(7).i <<= i32;
 		}
+
+		public void LocalTypeFromStore()
+		{
+			nint num = 42;
+			IntPtr zero = IntPtr.Zero;
+			nint zero2 = IntPtr.Zero;
+			nuint num2 = 43u;
+			nint num3 = i;
+			IntPtr intPtr = intptr;
+
+			Console.WriteLine();
+			zero2 = 1;
+			Console.WriteLine();
+
+			intptr = num;
+			intptr = zero;
+			intptr = zero2;
+			uintptr = num2;
+			intptr = num3;
+			intptr = intPtr;
+		}
+
+
+		public void LocalTypeFromUse()
+		{
+			IntPtr intPtr = intptr;
+			nint num = intptr;
+
+			Console.WriteLine();
+
+			intptr = intPtr;
+			i = num + 1;
+		}
 	}
 }

ICSharpCode.Decompiler.Tests/TestCases/Pretty/TupleTests.cs

@@ -146,9 +146,9 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		public void LocalVariables((int, int) a)
 		{
-			(int, int) valueTuple = (a.Item1 + a.Item2, a.Item1 * a.Item2);
-			Console.WriteLine(valueTuple.ToString());
-			Console.WriteLine(valueTuple.GetType().FullName);
+			(int, int) tuple = (a.Item1 + a.Item2, a.Item1 * a.Item2);
+			Console.WriteLine(tuple.ToString());
+			Console.WriteLine(tuple.GetType().FullName);
 		}
 
 		public void Foreach(IEnumerable<(int, string)> input)

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -165,6 +165,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				new HighLevelLoopTransform(),
 				new ReduceNestingTransform(),
 				new IntroduceDynamicTypeOnLocals(),
+				new IntroduceNativeIntTypeOnLocals(),
 				new AssignVariableNames(),
 			};
 		}

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -78,6 +78,7 @@
     <Compile Include="Disassembler\DisassemblerSignatureTypeProvider.cs" />
     <Compile Include="Documentation\XmlDocumentationElement.cs" />
     <Compile Include="IL\ControlFlow\AwaitInFinallyTransform.cs" />
+    <Compile Include="IL\Transforms\IntroduceNativeIntTypeOnLocals.cs" />
     <Compile Include="Solution\ProjectId.cs" />
     <Compile Include="Solution\ProjectItem.cs" />
     <Compile Include="Solution\SolutionCreator.cs" />

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -417,19 +417,28 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				type = NullableType.GetUnderlyingType(((TypeWithElementType)type).ElementType);
 			}
 
-			string name;
-			if (type is ArrayType) {
-				name = "array";
-			} else if (type is PointerType) {
-				name = "ptr";
-			} else if (type.Kind == TypeKind.TypeParameter || type.Kind == TypeKind.Unknown || type.Kind == TypeKind.Dynamic) {
-				name = "val";
-			} else if (type.Kind == TypeKind.ByReference) {
-				name = "reference";
-			} else if (type.IsAnonymousType()) {
+			string name = type.Kind switch
+			{
+				TypeKind.Array => "array",
+				TypeKind.Pointer => "ptr",
+				TypeKind.TypeParameter => "val",
+				TypeKind.Unknown => "val",
+				TypeKind.Dynamic => "val",
+				TypeKind.ByReference => "reference",
+				TypeKind.Tuple => "tuple",
+				TypeKind.NInt => "num",
+				TypeKind.NUInt => "num",
+				_ => null
+			};
+			if (name != null) {
+				return name;
+			}
+			if (type.IsAnonymousType()) {
 				name = "anon";
 			} else if (type.Name.EndsWith("Exception", StringComparison.Ordinal)) {
 				name = "ex";
+			} else if (type.IsCSharpNativeIntegerType()) {
+				name = "num";
 			} else if (!typeNameToVariableNameDict.TryGetValue(type.FullName, out name)) {
 				name = type.Name;
 				// remove the 'I' for interfaces

ICSharpCode.Decompiler/IL/Transforms/IntroduceNativeIntTypeOnLocals.cs

@@ -0,0 +1,78 @@
+// Copyright (c) 2020 Daniel Grunwald
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using ICSharpCode.Decompiler.IL.Transforms;
+using ICSharpCode.Decompiler.TypeSystem;
+
+namespace ICSharpCode.Decompiler.IL
+{
+	class IntroduceNativeIntTypeOnLocals : IILTransform
+	{
+		public void Run(ILFunction function, ILTransformContext context)
+		{
+			if (!context.Settings.NativeIntegers)
+				return;
+			foreach (var variable in function.Variables) {
+				if (variable.Kind != VariableKind.Local &&
+					variable.Kind != VariableKind.StackSlot &&
+					variable.Kind != VariableKind.ForeachLocal &&
+					variable.Kind != VariableKind.UsingLocal) {
+					continue;
+				}
+				if (!(variable.Type.IsKnownType(KnownTypeCode.IntPtr) || variable.Type.IsKnownType(KnownTypeCode.UIntPtr)))
+					continue;
+				bool isUsedAsNativeInt = variable.LoadInstructions.Any(IsUsedAsNativeInt);
+				bool isAssignedNativeInt = variable.StoreInstructions.Any(store => IsNativeIntStore(store, context.TypeSystem));
+				if (isUsedAsNativeInt || isAssignedNativeInt) {
+					variable.Type = variable.Type.GetSign() == Sign.Unsigned ? SpecialType.NUInt : SpecialType.NInt;
+				}
+			}
+		}
+
+		static bool IsUsedAsNativeInt(LdLoc load)
+		{
+			return load.Parent switch
+			{
+				BinaryNumericInstruction { UnderlyingResultType: StackType.I } => true,
+				BitNot { UnderlyingResultType: StackType.I } => true,
+				CallInstruction call => call.GetParameter(load.ChildIndex)?.Type.IsCSharpNativeIntegerType() ?? false,
+				_ => false,
+			};
+		}
+
+		static bool IsNativeIntStore(IStoreInstruction store, ICompilation compilation)
+		{
+			if (store is StLoc stloc) {
+				switch (stloc.Value) {
+					case BinaryNumericInstruction { UnderlyingResultType: StackType.I }:
+						return true;
+					case Conv { ResultType: StackType.I }:
+						return true;
+					default:
+						var inferredType = stloc.Value.InferType(compilation);
+						return inferredType.IsCSharpNativeIntegerType();
+				}
+			}
+			return false;
+		}
+	}
+}