Enhanced DivideBySize

This fixes some redundant IntPtr casts. Some tests are still failing.

Partially fixes #271

ICSharpCode.Decompiler/Ast/AstMethodBodyBuilder.cs

@@ -291,16 +291,10 @@ namespace ICSharpCode.Decompiler.Ast
 					{
 						BinaryOperatorExpression boe;
 						if (byteCode.InferredType is PointerType) {
-							if (byteCode.Arguments[0].ExpectedType is PointerType) {
-								arg2 = DivideBySize(arg2, ((PointerType)byteCode.InferredType).ElementType);
-								boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Add, arg2);
-								boe.AddAnnotation(IntroduceUnsafeModifier.PointerArithmeticAnnotation);
-							} else if (byteCode.Arguments[1].ExpectedType is PointerType) {
-								arg1 = DivideBySize(arg1, ((PointerType)byteCode.InferredType).ElementType);
-								boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Add, arg2);
+							boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Add, arg2);
+							if (byteCode.Arguments[0].ExpectedType is PointerType ||
+								byteCode.Arguments[1].ExpectedType is PointerType) {
 								boe.AddAnnotation(IntroduceUnsafeModifier.PointerArithmeticAnnotation);
-							} else {
-								boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Add, arg2);
 							}
 						} else {
 							boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Add, arg2);
@@ -314,12 +308,9 @@ namespace ICSharpCode.Decompiler.Ast
 					{
 						BinaryOperatorExpression boe;
 						if (byteCode.InferredType is PointerType) {
+							boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Subtract, arg2);
 							if (byteCode.Arguments[0].ExpectedType is PointerType) {
-								arg2 = DivideBySize(arg2, ((PointerType)byteCode.InferredType).ElementType);
-								boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Subtract, arg2);
 								boe.WithAnnotation(IntroduceUnsafeModifier.PointerArithmeticAnnotation);
-							} else {
-								boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Subtract, arg2);
 							}
 						} else {
 							boe = new Ast.BinaryOperatorExpression(arg1, BinaryOperatorType.Subtract, arg2);
@@ -706,7 +697,7 @@ namespace ICSharpCode.Decompiler.Ast
 						}
 						return new StackAllocExpression {
 							Type = AstBuilder.ConvertType(type),
-							CountExpression = DivideBySize(arg1, type)
+                            CountExpression = arg1
 						};
 					}
 				case ILCode.Mkrefany:
@@ -902,45 +893,6 @@ namespace ICSharpCode.Decompiler.Ast
 			}
 		}
 		
-		/// <summary>
-		/// Divides expr by the size of 'type'.
-		/// </summary>
-		Expression DivideBySize(Expression expr, TypeReference type)
-		{
-			CastExpression cast = expr as CastExpression;
-			if (cast != null && cast.Type is PrimitiveType && ((PrimitiveType)cast.Type).Keyword == "int")
-				expr = cast.Expression.Detach();
-			
-			Expression sizeOfExpression;
-			switch (TypeAnalysis.GetInformationAmount(type)) {
-				case 1:
-				case 8:
-					sizeOfExpression = new PrimitiveExpression(1);
-					break;
-				case 16:
-					sizeOfExpression = new PrimitiveExpression(2);
-					break;
-				case 32:
-					sizeOfExpression = new PrimitiveExpression(4);
-					break;
-				case 64:
-					sizeOfExpression = new PrimitiveExpression(8);
-					break;
-				default:
-					sizeOfExpression = new SizeOfExpression { Type = AstBuilder.ConvertType(type) };
-					break;
-			}
-			
-			BinaryOperatorExpression boe = expr as BinaryOperatorExpression;
-			if (boe != null && boe.Operator == BinaryOperatorType.Multiply && sizeOfExpression.IsMatch(boe.Right))
-				return boe.Left.Detach();
-			
-			if (sizeOfExpression.IsMatch(expr))
-				return new PrimitiveExpression(1);
-			
-			return new BinaryOperatorExpression(expr, BinaryOperatorType.Divide, sizeOfExpression);
-		}
-		
 		Expression MakeDefaultValue(TypeReference type)
 		{
 			TypeDefinition typeDef = type.Resolve();

ICSharpCode.Decompiler/ILAst/ILAstOptimizer.cs

@@ -39,6 +39,7 @@ namespace ICSharpCode.Decompiler.ILAst
 		PropertyAccessInstructions,
 		SplitToMovableBlocks,
 		TypeInference,
+		HandlePointerArithmetic,
 		SimplifyShortCircuit,
 		SimplifyTernaryOperator,
 		SimplifyNullCoalescing,
@@ -125,6 +126,9 @@ namespace ICSharpCode.Decompiler.ILAst
 			// Types are needed for the ternary operator optimization
 			TypeAnalysis.Run(context, method);
 			
+			if (abortBeforeStep == ILAstOptimizationStep.HandlePointerArithmetic) return;
+			HandlePointerArithmetic(method);
+
 			foreach(ILBlock block in method.GetSelfAndChildrenRecursive<ILBlock>()) {
 				bool modified;
 				do {
@@ -665,6 +669,107 @@ namespace ICSharpCode.Decompiler.ILAst
 				});
 		}
 
+		static void HandlePointerArithmetic(ILNode method)
+		{
+			foreach (ILExpression expr in method.GetSelfAndChildrenRecursive<ILExpression>()) {
+				List<ILExpression> args = expr.Arguments;
+				switch (expr.Code) {
+					case ILCode.Localloc:
+						args[0] = DivideBySize(args[0], ((PointerType)expr.InferredType).ElementType);
+						break;
+					case ILCode.Add:
+					case ILCode.Add_Ovf:
+					case ILCode.Add_Ovf_Un:
+						if (expr.InferredType is PointerType) {
+							if (args[0].ExpectedType is PointerType)
+								args[1] = DivideBySize(args[1], ((PointerType)expr.InferredType).ElementType);
+							else if (args[1].ExpectedType is PointerType)
+								args[0] = DivideBySize(args[0], ((PointerType)expr.InferredType).ElementType);
+						}
+						break;
+					case ILCode.Sub:
+					case ILCode.Sub_Ovf:
+					case ILCode.Sub_Ovf_Un:
+						if (expr.InferredType is PointerType) {
+							if (args[0].ExpectedType is PointerType)
+								args[1] = DivideBySize(args[1], ((PointerType)expr.InferredType).ElementType);
+						}
+						break;
+				}
+			}
+		}
+
+		static ILExpression UnwrapIntPtrCast(ILExpression expr)
+		{
+			if (expr.Code != ILCode.Conv_I && expr.Code != ILCode.Conv_U)
+				return expr;
+
+			ILExpression arg = expr.Arguments[0];
+			switch (arg.InferredType.MetadataType) {
+				case MetadataType.Byte:
+				case MetadataType.SByte:
+				case MetadataType.UInt16:
+				case MetadataType.Int16:
+				case MetadataType.UInt32:
+				case MetadataType.Int32:
+				case MetadataType.UInt64:
+				case MetadataType.Int64:
+					return arg;
+			}
+
+			return expr;
+		}
+
+		static ILExpression DivideBySize(ILExpression expr, TypeReference type)
+		{
+			expr = UnwrapIntPtrCast(expr);
+
+			ILExpression sizeOfExpression;
+			switch (TypeAnalysis.GetInformationAmount(type)) {
+				case 1:
+				case 8:
+					sizeOfExpression = new ILExpression(ILCode.Ldc_I4, 1);
+					break;
+				case 16:
+					sizeOfExpression = new ILExpression(ILCode.Ldc_I4, 2);
+					break;
+				case 32:
+					sizeOfExpression = new ILExpression(ILCode.Ldc_I4, 4);
+					break;
+				case 64:
+					sizeOfExpression = new ILExpression(ILCode.Ldc_I4, 8);
+					break;
+				default:
+					sizeOfExpression = new ILExpression(ILCode.Sizeof, type);
+					break;
+			}
+
+			if (expr.Code == ILCode.Mul || expr.Code == ILCode.Mul_Ovf || expr.Code == ILCode.Mul_Ovf_Un) {
+				ILExpression mulArg = expr.Arguments[1];
+				if (mulArg.Code == sizeOfExpression.Code && sizeOfExpression.Operand.Equals(mulArg.Operand))
+					return UnwrapIntPtrCast(expr.Arguments[0]);
+			}
+
+			if (expr.Code == sizeOfExpression.Code) {
+				if (sizeOfExpression.Operand.Equals(expr.Operand))
+					return new ILExpression(ILCode.Ldc_I4, 1);
+
+				if (expr.Code == ILCode.Ldc_I4) {
+					int offsetInBytes = (int)expr.Operand;
+					int elementSize = (int)sizeOfExpression.Operand;
+					int offsetInElements = offsetInBytes / elementSize;
+
+					// ensure integer division
+					if (offsetInElements * elementSize == offsetInBytes) {
+						expr.Operand = offsetInElements;
+						return expr;
+					}
+				}
+			}
+
+			return new ILExpression(ILCode.Div_Un, null, expr, sizeOfExpression);
+		}
+		
 		public static void ReplaceVariables(ILNode node, Func<ILVariable, ILVariable> variableMapping)
 		{
 			ILExpression expr = node as ILExpression;