Add transform "cgt.un(left, ldnull)" => "logic.not(ceq(left, ldnull))"

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -46,6 +46,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			new ControlFlowSimplification(),
 			new ILInlining(),
 			new TransformingVisitor(),
+			new ExpressionTransforms(),
 			new TransformValueTypeInitializers(),
 			new TransformArrayInitializers()
 		};

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -111,6 +111,7 @@
     <Compile Include="IL\Transforms\ILInlining.cs" />
     <Compile Include="IL\Transforms\LoopDetection.cs" />
     <Compile Include="IL\Transforms\OptimizingTransform.cs" />
+    <Compile Include="IL\Transforms\ExpressionTransforms.cs" />
     <Compile Include="IL\Transforms\TransformArrayInitializers.cs" />
     <Compile Include="IL\Transforms\TransformingVisitor.cs" />
     <Compile Include="CecilExtensions.cs" />

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -0,0 +1,58 @@
+// Copyright (c) 2014 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;
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+	/// <summary>
+	/// Collection of transforms that detect simple expression patterns
+	/// (e.g. 'cgt.un(..., ld.null)') and replace them with different instructions.
+	/// </summary>
+	/// <remarks>
+	/// Should run after inlining so that the expression patterns can be detected.
+	/// 
+	/// The transforms here do not open up new inlining opportunities.
+	/// </remarks>
+	public class ExpressionTransforms : IILTransform, ILVisitor
+	{
+		void IILTransform.Run(ILFunction function, ILTransformContext context)
+		{
+			function.AcceptVisitor(this);
+		}
+		
+		protected internal override void VisitCgt_Un(Cgt_Un inst)
+		{
+			base.VisitCgt_Un(inst);
+			if (inst.Right.MatchLdNull()) {
+				// cgt.un(left, ldnull)
+				// => logic.not(ceq(left, ldnull))
+				inst.ReplaceWith(new LogicNot(new Ceq(inst.Left, inst.Right) { ILRange = inst.ILRange }));
+			}
+		}
+		
+		protected internal override void VisitClt_Un(Clt_Un inst)
+		{
+			base.VisitClt_Un(inst);
+			if (inst.Left.MatchLdNull()) {
+				// clt.un(ldnull, right)
+				// => logic.not(ceq(ldnull, right))
+				inst.ReplaceWith(new LogicNot(new Ceq(inst.Left, inst.Right) { ILRange = inst.ILRange }));
+			}
+		}
+	}
+}

ICSharpCode.Decompiler/IL/Transforms/TransformingVisitor.cs

@@ -26,6 +26,7 @@ namespace ICSharpCode.Decompiler.IL
 {
 	/// <summary>
 	/// Visitor that applies a list of transformations to the IL Ast.
+	/// TODO: do we still need this, now that inlining is reverted back to the old ILInlining?
 	/// </summary>
 	/// <remarks>
 	/// The base class performs: