WIP

src/Compilers/CSharp/Portable/Binder/DecisionDagBuilder_ListPatterns.cs

@@ -40,7 +40,7 @@ private Tests MakeTestsAndBindingsForListPattern(BoundDagTemp input, BoundListPa
             {
                 Debug.Assert(list.LengthProperty is not null);
 
-                var lengthEvaluation = new BoundDagPropertyEvaluation(syntax, list.LengthProperty, input);
+                var lengthEvaluation = new BoundDagPropertyEvaluation(syntax, list.LengthProperty, isLengthOrCount: true, input);
                 tests.Add(new Tests.One(lengthEvaluation));
                 var lengthTemp = new BoundDagTemp(syntax, _compilation.GetSpecialType(SpecialType.System_Int32), lengthEvaluation);
                 tests.Add(new Tests.One(list.HasSlice

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -1429,6 +1429,7 @@
   </Node>
   <Node Name="BoundDagPropertyEvaluation" Base="BoundDagEvaluation">
     <Field Name="Property" Type="PropertySymbol" Null="disallow"/>
+    <Field Name="IsLengthOrCount" Type="bool"/>
   </Node>
   <Node Name="BoundDagIndexEvaluation" Base="BoundDagEvaluation">
     <Field Name="Property" Type="PropertySymbol" Null="disallow"/>

src/Compilers/CSharp/Portable/BoundTree/Constructors.cs

@@ -640,6 +640,14 @@ public BoundDagTemp(SyntaxNode syntax, TypeSymbol type, BoundDagEvaluation? sour
         public static BoundDagTemp ForOriginalInput(BoundExpression expr) => new BoundDagTemp(expr.Syntax, expr.Type!, source: null);
     }
 
+    internal partial class BoundDagPropertyEvaluation
+    {
+        public BoundDagPropertyEvaluation(SyntaxNode syntax, PropertySymbol property, BoundDagTemp input, bool hasErrors = false)
+            : this(syntax, property, isLengthOrCount: false, input, hasErrors)
+        {
+        }
+    }
+
     internal partial class BoundCompoundAssignmentOperator
     {
         public BoundCompoundAssignmentOperator(SyntaxNode syntax,

src/Compilers/CSharp/Portable/Utilities/IValueSet.cs

@@ -93,4 +93,9 @@ internal interface IValueSet<T> : IValueSet
         /// </summary>
         bool All(BinaryOperatorKind relation, T value);
     }
+
+    internal interface INumericValueSet<T> : IValueSet<T>
+    {
+        INumericValueSet<T> Shift(int offset);
+    }
 }

src/Compilers/CSharp/Portable/Utilities/ValueSetFactory.NumericValueSet.cs

@@ -6,6 +6,7 @@
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
@@ -19,7 +20,7 @@ internal static partial class ValueSetFactory
         /// <summary>
         /// The implementation of a value set for an numeric type <typeparamref name="T"/>.
         /// </summary>
-        private sealed class NumericValueSet<T, TTC> : IValueSet<T> where TTC : struct, INumericTC<T>
+        private sealed class NumericValueSet<T, TTC> : INumericValueSet<T> where TTC : struct, INumericTC<T>
         {
             private readonly ImmutableArray<(T first, T last)> _intervals;
 
@@ -51,6 +52,21 @@ internal NumericValueSet(ImmutableArray<(T first, T last)> intervals)
 
             public bool IsEmpty => _intervals.Length == 0;
 
+            INumericValueSet<T> INumericValueSet<T>.Shift(int offset)
+            {
+                Debug.Assert(this is NumericValueSet<int, IntTC>);
+                if (offset == 0)
+                    return this;
+                var builder = ArrayBuilder<(int first, int last)>.GetInstance();
+                foreach (var (first, last) in Unsafe.As<NumericValueSet<int, IntTC>>(this)._intervals)
+                {
+                    builder.Add((
+                        first == int.MaxValue ? first : first + offset,
+                        last == int.MaxValue ? last : last + offset));
+                }
+                return Unsafe.As<INumericValueSet<T>>(new NumericValueSet<int, IntTC>(builder.ToImmutableAndFree()));
+            }
+
             ConstantValue IValueSet.Sample
             {
                 get

src/Compilers/CSharp/Portable/Utilities/ValueSetFactory.cs

@@ -28,6 +28,8 @@ internal static partial class ValueSetFactory
         internal static readonly IValueSetFactory<int> ForNint = NintValueSetFactory.Instance;
         internal static readonly IValueSetFactory<uint> ForNuint = NuintValueSetFactory.Instance;
 
+        internal static readonly IValueSet PositiveIntValues = new NumericValueSet<int, IntTC>(0, int.MaxValue);
+
         public static IValueSetFactory? ForSpecialType(SpecialType specialType, bool isNative = false)
         {
             switch (specialType)