Do not transforms pattern further as if they were real instructions.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -29,6 +29,7 @@ using ICSharpCode.Decompiler.CSharp.Resolver;
 using ICSharpCode.Decompiler.CSharp.Syntax;
 using ICSharpCode.Decompiler.CSharp.Transforms;
 using ICSharpCode.Decompiler.IL;
+using ICSharpCode.Decompiler.IL.Patterns;
 using ICSharpCode.Decompiler.IL.Transforms;
 using ICSharpCode.Decompiler.Semantics;
 using ICSharpCode.Decompiler.TypeSystem;
@@ -5387,6 +5388,16 @@ namespace ICSharpCode.Decompiler.CSharp
 							.WithILInstruction(matchInstruction);
 					}
 				case Comp comp:
+					if (comp.MatchLogicNot(out var operand) && MatchInstruction.IsPatternMatch(operand, out _, settings))
+					{
+						// logic.not as a pattern
+						Expression sub = TranslatePattern(operand, leftHandType).Expression;
+						if (sub is UnaryOperatorExpression { Operator: UnaryOperatorType.PatternNot } uoe)
+						{
+							return uoe.Expression.Detach().WithILInstruction(comp);
+						}
+						return new UnaryOperatorExpression(UnaryOperatorType.PatternNot, sub).WithILInstruction(comp);
+					}
 					TranslatedExpression constantValue;
 					if (comp.Right is DefaultValue dv)
 					{

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -599,18 +599,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				context.Step("conditional operator", inst);
 				IType type = v.Type;
-				// Try to tighten the type; this matters esp. for logic.and/logic.or:
+				// Try to tighten the type to `bool`; this matters esp. for logic.and/logic.or:
 				IType type1 = value1.InferType(context.TypeSystem);
 				IType type2 = value2.InferType(context.TypeSystem);
-				if (type1.IsKnownType(KnownTypeCode.Boolean) && (
+				if (type1.IsKnownType(KnownTypeCode.Boolean)
-					type2.IsKnownType(KnownTypeCode.Boolean)
+					&& (type2.IsKnownType(KnownTypeCode.Boolean) || value2 is LdcI4 { Value: 0 or 1 }))
-					|| value2 is LdcI4 { Value: 0 or 1 }
-				))
 				{
 					type = type1;
 				}
-				else if (type2.IsKnownType(KnownTypeCode.Boolean)
+				else if (type2.IsKnownType(KnownTypeCode.Boolean) && value1 is LdcI4 { Value: 0 or 1 })
-				 && value1 is LdcI4 { Value: 0 or 1 })
 				{
 					type = type2;
 				}
@@ -1024,5 +1021,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				context.EndStep(condition);
 			}
 		}
+
+		protected internal override void VisitMatchInstruction(MatchInstruction inst)
+		{
+			inst.TestedOperand.AcceptVisitor(this);
+			// Do not recurse into the sub-patterns: patterns are restricted to use only certain ILInstructions,
+			// and arbitrary transforms might not stay within that allowed set of instructions.
+		}
 	}
 }

ILSpy-tests

@@ -1 +1 @@
-Subproject commit 4ccc3f0108007242c95025590edd4cc6ef1fb731
+Subproject commit 9668d49b9f71b40045e5417b55d20e330be95921