Translate MatchInstruction to BinaryOperatorExpression with BinaryOperatorType.IsPattern.

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

@@ -24,6 +24,42 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return F() && x is string w && w.Contains("a");
 		}
 
+		public void SimpleTypePatternWithShortcircuitAnd(object x)
+		{
+			if (x is string z && z.Contains("a"))
+			{
+				Console.WriteLine(z);
+			}
+			else
+			{
+				Console.WriteLine();
+			}
+		}
+
+		public void SimpleTypePatternWithShortcircuitOr(object x)
+		{
+			if (!(x is string z) || z.Contains("a"))
+			{
+				Console.WriteLine();
+			}
+			else
+			{
+				Console.WriteLine(z);
+			}
+		}
+
+		public void SimpleTypePatternWithShortcircuitOr2(object x)
+		{
+			if (F() || !(x is string z))
+			{
+				Console.WriteLine();
+			}
+			else
+			{
+				Console.WriteLine(z);
+			}
+		}
+
 		private bool F()
 		{
 			return true;

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -89,6 +89,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				new SplitVariables(),
 				new ILInlining(),
 				new InlineReturnTransform(), // must run before DetectPinnedRegions
+				new RemoveInfeasiblePathTransform(),
 				new DetectPinnedRegions(), // must run after inlining but before non-critical control flow transforms
 				new YieldReturnDecompiler(), // must run after inlining but before loop detection
 				new AsyncAwaitDecompiler(),  // must run after inlining but before loop detection

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -4340,7 +4340,44 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		protected internal override TranslatedExpression VisitMatchInstruction(MatchInstruction inst, TranslationContext context)
 		{
-			throw new NotImplementedException();
+			var left = Translate(inst.TestedOperand);
+			var right = TranslatePattern(inst);
+
+			return new BinaryOperatorExpression(left, BinaryOperatorType.IsPattern, right)
+				.WithRR(new ResolveResult(compilation.FindType(KnownTypeCode.Boolean)))
+				.WithILInstruction(inst);
+		}
+
+		ExpressionWithILInstruction TranslatePattern(ILInstruction pattern)
+		{
+			switch (pattern)
+			{
+				case MatchInstruction matchInstruction:
+					if (!matchInstruction.CheckType)
+						throw new NotImplementedException();
+					if (matchInstruction.IsDeconstructCall)
+						throw new NotImplementedException();
+					if (matchInstruction.IsDeconstructTuple)
+						throw new NotImplementedException();
+					if (matchInstruction.SubPatterns.Any())
+						throw new NotImplementedException();
+					if (matchInstruction.HasDesignator)
+					{
+						SingleVariableDesignation designator = new SingleVariableDesignation { Identifier = matchInstruction.Variable.Name };
+						designator.AddAnnotation(new ILVariableResolveResult(matchInstruction.Variable));
+						return new DeclarationExpression {
+							Type = ConvertType(matchInstruction.Variable.Type),
+							Designation = designator
+						}.WithILInstruction(matchInstruction);
+					}
+					else
+					{
+						return new TypeReferenceExpression(ConvertType(matchInstruction.Variable.Type))
+							.WithILInstruction(matchInstruction);
+					}
+				default:
+					throw new NotImplementedException();
+			}
 		}
 
 		protected internal override TranslatedExpression VisitInvalidBranch(InvalidBranch inst, TranslationContext context)

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -822,6 +822,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 					spacePolicy = policy.SpaceAroundShiftOperator;
 					break;
 				case BinaryOperatorType.NullCoalescing:
+				case BinaryOperatorType.IsPattern:
 					spacePolicy = true;
 					break;
 				case BinaryOperatorType.Range:
@@ -831,7 +832,15 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 					throw new NotSupportedException("Invalid value for BinaryOperatorType");
 			}
 			Space(spacePolicy);
-			WriteToken(BinaryOperatorExpression.GetOperatorRole(binaryOperatorExpression.Operator));
+			TokenRole tokenRole = BinaryOperatorExpression.GetOperatorRole(binaryOperatorExpression.Operator);
+			if (tokenRole == BinaryOperatorExpression.IsKeywordRole)
+			{
+				WriteKeyword(tokenRole);
+			}
+			else
+			{
+				WriteToken(tokenRole);
+			}
 			Space(spacePolicy);
 			binaryOperatorExpression.Right.AcceptVisitor(this);
 			EndNode(binaryOperatorExpression);
@@ -2788,7 +2797,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public virtual void VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation)
 		{
 			StartNode(singleVariableDesignation);
-			writer.WriteIdentifier(singleVariableDesignation.IdentifierToken);
+			WriteIdentifier(singleVariableDesignation.IdentifierToken);
 			EndNode(singleVariableDesignation);
 		}
 

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertParenthesesVisitor.cs

@@ -143,6 +143,8 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 						return PrecedenceLevel.ConditionalOr;
 					case BinaryOperatorType.NullCoalescing:
 						return PrecedenceLevel.NullCoalescing;
+					case BinaryOperatorType.IsPattern:
+						return PrecedenceLevel.RelationalAndTypeTesting;
 					default:
 						throw new NotSupportedException("Invalid value for BinaryOperatorType");
 				}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/BinaryOperatorExpression.cs

@@ -25,7 +25,6 @@
 // THE SOFTWARE.
 
 using System;
-using System.Collections.Generic;
 using System.Linq.Expressions;
 
 namespace ICSharpCode.Decompiler.CSharp.Syntax
@@ -55,6 +54,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public readonly static TokenRole ShiftRightRole = new TokenRole(">>");
 		public readonly static TokenRole NullCoalescingRole = new TokenRole("??");
 		public readonly static TokenRole RangeRole = new TokenRole("..");
+		public readonly static TokenRole IsKeywordRole = IsExpression.IsKeywordRole;
 
 		public readonly static Role<Expression> LeftRole = new Role<Expression>("Left", Expression.Null);
 		public readonly static Role<Expression> RightRole = new Role<Expression>("Right", Expression.Null);
@@ -155,6 +155,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 					return NullCoalescingRole;
 				case BinaryOperatorType.Range:
 					return RangeRole;
+				case BinaryOperatorType.IsPattern:
+					return IsKeywordRole;
 				default:
 					throw new NotSupportedException("Invalid value for BinaryOperatorType");
 			}
@@ -265,6 +267,10 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		NullCoalescing,
 		/// <summary>left .. right</summary>
 		/// <remarks>left and right are optional = may be Expression.Null</remarks>
-		Range
+		Range,
+
+		/// <summary>left is right</summary>
+		/// <remarks>right must be a pattern</remarks>
+		IsPattern,
 	}
 }

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -355,6 +355,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				case VariableKind.ExceptionStackSlot:
 				case VariableKind.UsingLocal:
 				case VariableKind.ForeachLocal:
+				case VariableKind.PatternLocal:
 					return false;
 				default:
 					return true;

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -1446,6 +1446,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool patternMatching = true;
+
+		/// <summary>
+		/// Gets/Sets whether C# 7.0 pattern matching should be detected.
+		/// </summary>
+		[Category("C# 7.0 / VS 2017")]
+		[Description("DecompilerSettings.PatternMatching")]
+		public bool PatternMatching {
+			get { return patternMatching; }
+			set {
+				if (patternMatching != value)
+				{
+					patternMatching = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool staticLocalFunctions = true;
 
 		/// <summary>

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -94,6 +94,7 @@
     <Compile Include="IL\Transforms\IntroduceNativeIntTypeOnLocals.cs" />
     <Compile Include="IL\Transforms\LdLocaDupInitObjTransform.cs" />
     <Compile Include="IL\Transforms\PatternMatchingTransform.cs" />
+    <Compile Include="IL\Transforms\RemoveInfeasiblePathTransform.cs" />
     <Compile Include="Metadata\ReferenceLoadInfo.cs" />
     <Compile Include="Semantics\OutVarResolveResult.cs" />
     <Compile Include="SingleFileBundle.cs" />

ICSharpCode.Decompiler/IL/Transforms/PatternMatchingTransform.cs

@@ -18,7 +18,6 @@
 
 #nullable enable
 
-
 namespace ICSharpCode.Decompiler.IL.Transforms
 {
 
@@ -32,6 +31,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		void IStatementTransform.Run(Block block, int pos, StatementTransformContext context)
 		{
+			if (!context.Settings.PatternMatching)
+				return;
 			if (pos + 1 >= block.Instructions.Count)
 				return;
 			if (block.Instructions[pos] is not StLoc
@@ -54,17 +55,33 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return;
 			if (result.LoadInst is not LdLoc)
 				return;
-			if (!result.LoadInst.Parent!.MatchCompNotEqualsNull(out _))
+			bool invertCondition;
+			if (result.LoadInst.Parent!.MatchCompNotEqualsNull(out _))
+			{
+				invertCondition = false;
+
+			}
+			else if (result.LoadInst.Parent!.MatchCompEqualsNull(out _))
+			{
+				invertCondition = true;
+			}
+			else
+			{
 				return;
+			}
 
 			context.Step($"Type pattern matching {v.Name}", block.Instructions[pos]);
 			// call Use(..., match.type[T](V = testedOperand))
 
 			var target = result.LoadInst.Parent;
-			var matchInstruction = new MatchInstruction(v, testedOperand) {
+			ILInstruction matchInstruction = new MatchInstruction(v, testedOperand) {
 				CheckNotNull = true,
 				CheckType = true
 			};
+			if (invertCondition)
+			{
+				matchInstruction = Comp.LogicNot(matchInstruction);
+			}
 			target.ReplaceWith(matchInstruction.WithILRange(target));
 			block.Instructions.RemoveAt(pos);
 			v.Kind = VariableKind.PatternLocal;

ICSharpCode.Decompiler/IL/Transforms/RemoveInfeasiblePathTransform.cs

@@ -0,0 +1,116 @@
+// Copyright (c) 2021 Daniel Grunwald, 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.
+
+#nullable enable
+
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+	/// <summary>
+	/// Block IL_0018 (incoming: *) {
+	///     stloc s(ldc.i4 1)
+	///     br IL_0019
+	/// }
+	/// 
+	/// Block IL_0019 (incoming: > 1) {
+	///     if (logic.not(ldloc s)) br IL_0027
+	///     br IL_001d
+	/// }
+	/// 
+	/// replace br IL_0019 with br IL_0027
+	/// </summary>
+	class RemoveInfeasiblePathTransform : IILTransform
+	{
+		void IILTransform.Run(ILFunction function, ILTransformContext context)
+		{
+			foreach (var container in function.Descendants.OfType<BlockContainer>())
+			{
+				bool changed = false;
+				foreach (var block in container.Blocks)
+				{
+					changed |= DoTransform(block, context);
+				}
+
+				if (changed)
+				{
+					container.SortBlocks(deleteUnreachableBlocks: true);
+				}
+			}
+		}
+
+
+		private bool DoTransform(Block block, ILTransformContext context)
+		{
+			if (!MatchBlock1(block, out var s, out int value, out var br))
+				return false;
+			if (!MatchBlock2(br.TargetBlock, s, value, out var targetBlock))
+				return false;
+			context.Step("RemoveInfeasiblePath", br);
+			br.TargetBlock = targetBlock;
+			return true;
+		}
+
+		// Block IL_0018 (incoming: *) {
+		//  stloc s(ldc.i4 1)
+		//  br IL_0019
+		// }
+		private bool MatchBlock1(Block block, [NotNullWhen(true)] out ILVariable? variable, out int constantValue, [NotNullWhen(true)] out Branch? branch)
+		{
+			variable = null;
+			constantValue = 0;
+			branch = null;
+			if (block.Instructions.Count != 2)
+				return false;
+			if (block.Instructions[0] is not StLoc
+				{
+					Variable: { Kind: VariableKind.StackSlot } s,
+					Value: LdcI4 { Value: 0 or 1 } valueInst
+				})
+			{
+				return false;
+			}
+			if (block.Instructions[1] is not Branch br)
+				return false;
+			variable = s;
+			constantValue = valueInst.Value;
+			branch = br;
+			return true;
+		}
+
+		// Block IL_0019 (incoming: > 1) {
+		//     if (logic.not(ldloc s)) br IL_0027
+		//     br IL_001d
+		// }
+		bool MatchBlock2(Block block, ILVariable s, int constantValue, [NotNullWhen(true)] out Block? targetBlock)
+		{
+			targetBlock = null;
+			if (block.Instructions.Count != 2)
+				return false;
+			if (block.IncomingEdgeCount <= 1)
+				return false;
+			if (!block.MatchIfAtEndOfBlock(out var load, out var trueInst, out var falseInst))
+				return false;
+			if (!load.MatchLdLoc(s))
+				return false;
+			ILInstruction target = constantValue != 0 ? trueInst : falseInst;
+			return target.MatchBranch(out targetBlock);
+		}
+	}
+}