Also combine 'ldlen; conv.i4.ovf' to 'ldlen.i4'.

The VB compiler emits overflow checks when accessing the array length. (#1097)

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -568,6 +568,21 @@ namespace ICSharpCode.Decompiler
 		}
 
 		#region Options to aid VB decompilation
+		bool assumeArrayLengthFitsIntoInt32 = true;
+
+		/// <summary>
+		/// Gets/Sets whether the decompiler can assume that 'ldlen; conv.i4.ovf' does not throw an overflow exception.
+		/// </summary>
+		public bool AssumeArrayLengthFitsIntoInt32 {
+			get { return assumeArrayLengthFitsIntoInt32; }
+			set {
+				if (assumeArrayLengthFitsIntoInt32 != value) {
+					assumeArrayLengthFitsIntoInt32 = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool introduceIncrementAndDecrement = true;
 
 		/// <summary>

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -148,7 +148,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		protected internal override void VisitConv(Conv inst)
 		{
 			inst.Argument.AcceptVisitor(this);
-			if (inst.Argument.MatchLdLen(StackType.I, out ILInstruction array) && inst.TargetType.IsIntegerType() && !inst.CheckForOverflow) {
+			if (inst.Argument.MatchLdLen(StackType.I, out ILInstruction array) && inst.TargetType.IsIntegerType()
+				&& (!inst.CheckForOverflow || context.Settings.AssumeArrayLengthFitsIntoInt32))
+			{
 				context.Step("conv.i4(ldlen array) => ldlen.i4(array)", inst);
 				inst.AddILRange(inst.Argument.ILRange);
 				inst.ReplaceWith(new LdLen(inst.TargetType.GetStackType(), array) { ILRange = inst.ILRange });