Don't match sub.ovf in SwitchAnalysis.

ICSharpCode.Decompiler/IL/ControlFlow/SwitchAnalysis.cs

@@ -233,21 +233,17 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 
 		bool MatchSwitchVar(ILInstruction inst, out long sub)
 		{
-			if (inst.MatchBinaryNumericInstruction(BinaryNumericOperator.Sub, out var left, out var right) && right.MatchLdcI(out sub))
-				return MatchSwitchVar(left);
+			if (inst is BinaryNumericInstruction bn
+				&& bn.Operator == BinaryNumericOperator.Sub
+				&& !bn.CheckForOverflow && !bn.IsLifted
+				&& bn.Right.MatchLdcI(out sub))
+			{
+				return MatchSwitchVar(bn.Left);
+			}
 
 			sub = 0;
 			return MatchSwitchVar(inst);
 		}
-		/// <summary>
-		/// Shifts a LongInterval, treating long.MinValue and long.MaxValue like float.Positive/NegativeInfinity
-		/// </summary>
-		LongInterval ShiftInterval(LongInterval interval, long offset)
-		{
-			return new LongInterval(
-				interval.Start == long.MinValue ? long.MinValue : interval.Start + offset,
-				interval.End == long.MinValue ? long.MinValue : interval.End + offset);
-		}
 
 		/// <summary>
 		/// Analyzes the boolean condition, returning the set of values of the interesting
@@ -256,11 +252,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		private bool AnalyzeCondition(ILInstruction condition, out LongSet trueValues)
 		{
 			if (condition is Comp comp && MatchSwitchVar(comp.Left, out var sub) && comp.Right.MatchLdcI(out long val)) {
-				// if (comp(V OP val))
+				// if (comp((V - sub) OP val))
 				trueValues = MakeSetWhereComparisonIsTrue(comp.Kind, val, comp.Sign);
-				if (sub != 0)
-					trueValues = new LongSet(trueValues.Intervals.Select(i => ShiftInterval(i, sub)));
-
+				trueValues = trueValues.AddOffset(sub);
 				return true;
 			} else if (MatchSwitchVar(condition)) {
 				// if (ldloc V) --> branch for all values except 0

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -200,27 +200,28 @@ namespace ICSharpCode.Decompiler.Util
 		/// </summary>
 		public static IEnumerable<T> Merge<T>(this IEnumerable<T> input1, IEnumerable<T> input2, Comparison<T> comparison)
 		{
-			var enumA = input1.GetEnumerator();
-			var enumB = input2.GetEnumerator();
-			bool moreA = enumA.MoveNext();
-			bool moreB = enumB.MoveNext();
-			while (moreA && moreB) {
-				if (comparison(enumA.Current, enumB.Current) <= 0) {
+			using (var enumA = input1.GetEnumerator())
+			using (var enumB = input2.GetEnumerator()) {
+				bool moreA = enumA.MoveNext();
+				bool moreB = enumB.MoveNext();
+				while (moreA && moreB) {
+					if (comparison(enumA.Current, enumB.Current) <= 0) {
+						yield return enumA.Current;
+						moreA = enumA.MoveNext();
+					} else {
+						yield return enumB.Current;
+						moreB = enumB.MoveNext();
+					}
+				}
+				while (moreA) {
 					yield return enumA.Current;
 					moreA = enumA.MoveNext();
-				} else {
+				}
+				while (moreB) {
 					yield return enumB.Current;
 					moreB = enumB.MoveNext();
 				}
 			}
-			while (moreA) {
-				yield return enumA.Current;
-				moreA = enumA.MoveNext();
-			}
-			while (moreB) {
-				yield return enumB.Current;
-				moreB = enumB.MoveNext();
-			}
 		}
 
 		/// <summary>

ICSharpCode.Decompiler/Util/LongSet.cs

@@ -203,6 +203,9 @@ namespace ICSharpCode.Decompiler.Util
 		/// </summary>
 		public LongSet AddOffset(long val)
 		{
+			if (val == 0) {
+				return this;
+			}
 			var newIntervals = new List<LongInterval>(Intervals.Length + 1);
 			foreach (var element in Intervals) {
 				long newStart = unchecked(element.Start + val);