Initial implementation of the pattern matching transform.

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -107,6 +107,7 @@
     <Compile Include="TestCases\Correctness\DeconstructionTests.cs" />
     <Compile Include="TestCases\Correctness\DynamicTests.cs" />
     <Compile Include="TestCases\Correctness\StringConcat.cs" />
+    <Compile Include="TestCases\Pretty\PatternMatching.cs" />
     <Compile Include="TestCases\VBPretty\VBPropertiesTest.cs" />
     <None Include="TestCases\ILPretty\Issue2260SwitchString.cs" />
     <None Include="TestCases\Pretty\Records.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -304,6 +304,12 @@ namespace ICSharpCode.Decompiler.Tests
 			RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public void PatternMatching([ValueSource(nameof(roslyn2OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void InitializerTests([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

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

@@ -21,7 +21,7 @@ using System.Collections.Generic;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
-	public class PatternMatching
+	public class OutVariables
 	{
 		public static void OutVarInShortCircuit(Dictionary<int, string> d)
 		{

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

@@ -0,0 +1,36 @@
+using System;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class PatternMatching
+	{
+		public bool SimpleTypePattern(object x)
+		{
+			Use(x is string y);
+			if (x is string z)
+			{
+				Console.WriteLine(z);
+			}
+			return x is string w;
+		}
+
+		public bool SimpleTypePatternWithShortcircuit(object x)
+		{
+			Use(F() && x is string y && y.Contains("a"));
+			if (F() && x is string z && z.Contains("a"))
+			{
+				Console.WriteLine(z);
+			}
+			return F() && x is string w && w.Contains("a");
+		}
+
+		private bool F()
+		{
+			return true;
+		}
+
+		private void Use(bool x)
+		{
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -136,6 +136,7 @@ namespace ICSharpCode.Decompiler.CSharp
 							// Inlining must be first, because it doesn't trigger re-runs.
 							// Any other transform that opens up new inlining opportunities should call RequestRerun().
 							new ExpressionTransforms(),
+							new PatternMatchingTransform(),
 							new DynamicIsEventAssignmentTransform(),
 							new TransformAssignment(), // inline and compound assignments
 							new NullCoalescingTransform(),

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -4338,6 +4338,11 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
+		protected internal override TranslatedExpression VisitMatchInstruction(MatchInstruction inst, TranslationContext context)
+		{
+			throw new NotImplementedException();
+		}
+
 		protected internal override TranslatedExpression VisitInvalidBranch(InvalidBranch inst, TranslationContext context)
 		{
 			string message = "Error";

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -93,6 +93,7 @@
     <Compile Include="IL\ControlFlow\AwaitInFinallyTransform.cs" />
     <Compile Include="IL\Transforms\IntroduceNativeIntTypeOnLocals.cs" />
     <Compile Include="IL\Transforms\LdLocaDupInitObjTransform.cs" />
+    <Compile Include="IL\Transforms\PatternMatchingTransform.cs" />
     <Compile Include="Metadata\ReferenceLoadInfo.cs" />
     <Compile Include="Semantics\OutVarResolveResult.cs" />
     <Compile Include="SingleFileBundle.cs" />

ICSharpCode.Decompiler/IL/Instructions/MatchInstruction.cs

@@ -84,7 +84,7 @@ namespace ICSharpCode.Decompiler.IL
 					comp(deconstruct.result1(c) == 1),
 					match.type[D].deconstruct(d = deconstruct.result2(c)) {
 						comp(deconstruct.result1(d) == 2),
-						comp(deconstruct.result2(d) == 2),
+						comp(deconstruct.result2(d) == 3),
 					}
 				}
 		 */
@@ -126,10 +126,15 @@ namespace ICSharpCode.Decompiler.IL
 					testedOperand = m.testedOperand;
 					return true;
 				case Comp comp:
-					testedOperand = comp.Left;
-					return IsConstant(comp.Right);
-				case ILInstruction logicNot when logicNot.MatchLogicNot(out var operand):
-					return IsPatternMatch(operand, out testedOperand);
+					if (comp.MatchLogicNot(out var operand))
+					{
+						return IsPatternMatch(operand, out testedOperand);
+					}
+					else
+					{
+						testedOperand = comp.Left;
+						return IsConstant(comp.Right);
+					}
 				default:
 					testedOperand = null;
 					return false;
@@ -145,6 +150,7 @@ namespace ICSharpCode.Decompiler.IL
 				OpCode.LdcI4 => true,
 				OpCode.LdcI8 => true,
 				OpCode.LdNull => true,
+				OpCode.LdStr => true,
 				_ => false
 			};
 		}

ICSharpCode.Decompiler/IL/Transforms/PatternMatchingTransform.cs

@@ -0,0 +1,73 @@
+// 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
+
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+
+	class PatternMatchingTransform : IStatementTransform
+	{
+		/// <summary>
+		/// stloc V(isinst T(testedOperand))
+		/// call Use(..., comp.o(ldloc V != ldnull))
+		/// =>
+		/// call Use(..., match.type[T](V = testedOperand))
+		/// </summary>
+		void IStatementTransform.Run(Block block, int pos, StatementTransformContext context)
+		{
+			if (pos + 1 >= block.Instructions.Count)
+				return;
+			if (block.Instructions[pos] is not StLoc
+				{
+					Variable: var v,
+					Value: IsInst { Argument: var testedOperand, Type: var type }
+				})
+			{
+				return;
+			}
+			if (!v.IsSingleDefinition)
+				return;
+			if (v.Kind is not (VariableKind.Local or VariableKind.StackSlot))
+				return;
+			if (!v.Type.Equals(type))
+				return;
+
+			var result = ILInlining.FindLoadInNext(block.Instructions[pos + 1], v, testedOperand, InliningOptions.None);
+			if (result.Type != ILInlining.FindResultType.Found)
+				return;
+			if (result.LoadInst is not LdLoc)
+				return;
+			if (!result.LoadInst.Parent!.MatchCompNotEqualsNull(out _))
+				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) {
+				CheckNotNull = true,
+				CheckType = true
+			};
+			target.ReplaceWith(matchInstruction.WithILRange(target));
+			block.Instructions.RemoveAt(pos);
+			v.Kind = VariableKind.PatternLocal;
+		}
+	}
+}

ICSharpCode.Decompiler/IL/Transforms/StatementTransform.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Diagnostics;