HighLevelLoopTransform: Add support for while (condition) loops

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -134,6 +134,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				},
 				new ProxyCallReplacer(),
 				new DelegateConstruction(),
+				new HighLevelLoopTransform(),
 				new AssignVariableNames(),
 			};
 		}

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -281,6 +281,7 @@
     <Compile Include="IL\Instructions\CallIndirect.cs" />
     <Compile Include="IL\Instructions\DefaultValue.cs" />
     <Compile Include="IL\Transforms\EarlyExpressionTransforms.cs" />
+    <Compile Include="IL\Transforms\HighLevelLoopTransform.cs" />
     <Compile Include="IL\Transforms\ProxyCallReplacer.cs" />
     <Compile Include="IL\Instructions\StringToInt.cs" />
     <Compile Include="IL\Instructions\UsingInstruction.cs" />

ICSharpCode.Decompiler/IL/Transforms/HighLevelLoopTransform.cs

@@ -0,0 +1,104 @@
+// Copyright (c) 2017 Siegfried Pammer
+// 
+// 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;
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+	/// <summary>
+	/// If possible, transforms plain ILAst loops into while (condition), do-while and for-loops.
+	/// </summary>
+	public class HighLevelLoopTransform : IILTransform
+	{
+		public void Run(ILFunction function, ILTransformContext context)
+		{
+			foreach (var loop in function.Descendants.OfType<BlockContainer>()) {
+				if (loop.Kind != ContainerKind.Loop)
+					continue;
+				if (MatchWhileLoop(loop, out var loopBody)) {
+					MatchForLoop(loop, loopBody);
+					continue;
+				}
+				if (MatchDoWhileLoop(loop))
+					continue;
+			}
+		}
+
+		bool MatchWhileLoop(BlockContainer loop, out Block loopBody)
+		{
+			// while-loop:
+			// if (loop-condition) br loop-content-block
+			// leave loop-container
+			// -or-
+			// if (loop-condition) block content-block
+			// leave loop-container
+			loopBody = null;
+			if (loop.EntryPoint.Instructions.Count != 2)
+				return false;
+			if (!(loop.EntryPoint.Instructions[0] is IfInstruction ifInstruction))
+				return false;
+			if (!ifInstruction.FalseInst.MatchNop())
+				return false;
+			var trueInst = ifInstruction.TrueInst;
+			if (!loop.EntryPoint.Instructions[1].MatchLeave(loop))
+				return false;
+			if (trueInst is Block b) {
+				loopBody = b;
+				if (!MatchWhileLoopBody(loopBody, loop))
+					return false;
+				trueInst.ReplaceWith(new Branch(loopBody));
+				loop.Blocks.Insert(1, loopBody);
+			} else if (trueInst is Branch br) {
+				loopBody = br.TargetBlock;
+				if (!MatchWhileLoopBody(loopBody, loop))
+					return false;
+			} else {
+				return false;
+			}
+			ifInstruction.FalseInst = loop.EntryPoint.Instructions[1];
+			loop.EntryPoint.Instructions.RemoveAt(1);
+			loop.Kind = ContainerKind.While;
+			return true;
+		}
+
+		/// <summary>
+		/// The last instruction of the while body must be a branch to the loop head.
+		/// </summary>
+		bool MatchWhileLoopBody(Block loopBody, BlockContainer loop)
+		{
+			if (loopBody.Instructions.Count == 0)
+				return false;
+			if (!loopBody.Instructions.Last().MatchBranch(loop.EntryPoint))
+				return false;
+			return true;
+		}
+
+		bool MatchDoWhileLoop(BlockContainer loop)
+		{
+			return false;
+		}
+
+		bool MatchForLoop(BlockContainer loop, Block whileLoopBody)
+		{
+			return false;
+		}
+	}
+}