Manually optimize a rem 64 instruction to avoid regression on runtimes which do not currently optimize it (#96203)

Author: andrewjsaid

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.cs

@@ -166,7 +166,7 @@ private static FrozenDictionary<TKey, TValue> CreateFromDictionary<TKey, TValue>
                 {
                     if (key.Length < minLength) minLength = key.Length;
                     if (key.Length > maxLength) maxLength = key.Length;
-                    lengthFilter |= (1UL << (key.Length % 64));
+                    lengthFilter |= (1UL << (key.Length & 0x3F));
                 }
                 Debug.Assert(minLength >= 0 && maxLength >= minLength);
 

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenSet.cs

@@ -114,7 +114,7 @@ private static FrozenSet<T> CreateFromSet<T>(HashSet<T> source)
                 {
                     if (s.Length < minLength) minLength = s.Length;
                     if (s.Length > maxLength) maxLength = s.Length;
-                    lengthFilter |= (1UL << (s.Length % 64));
+                    lengthFilter |= (1UL << (s.Length & 0x3F));
                 }
                 Debug.Assert(minLength >= 0 && maxLength >= minLength);
 

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenDictionary_Full.cs

@@ -28,6 +28,6 @@ internal OrdinalStringFrozenDictionary_Full(
 
         private protected override bool Equals(string? x, string? y) => string.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinal(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenDictionary_FullCaseInsensitive.cs

@@ -28,6 +28,6 @@ internal OrdinalStringFrozenDictionary_FullCaseInsensitive(
 
         private protected override bool Equals(string? x, string? y) => StringComparer.OrdinalIgnoreCase.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinalIgnoreCase(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenDictionary_FullCaseInsensitiveAscii.cs

@@ -28,6 +28,6 @@ internal OrdinalStringFrozenDictionary_FullCaseInsensitiveAscii(
 
         private protected override bool Equals(string? x, string? y) => StringComparer.OrdinalIgnoreCase.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinalIgnoreCaseAscii(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenSet_Full.cs

@@ -27,6 +27,6 @@ internal OrdinalStringFrozenSet_Full(
 
         private protected override bool Equals(string? x, string? y) => string.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinal(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenSet_FullCaseInsensitive.cs

@@ -27,6 +27,6 @@ internal OrdinalStringFrozenSet_FullCaseInsensitive(
 
         private protected override bool Equals(string? x, string? y) => StringComparer.OrdinalIgnoreCase.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinalIgnoreCase(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/String/OrdinalStringFrozenSet_FullCaseInsensitiveAscii.cs

@@ -27,6 +27,6 @@ internal OrdinalStringFrozenSet_FullCaseInsensitiveAscii(
 
         private protected override bool Equals(string? x, string? y) => StringComparer.OrdinalIgnoreCase.Equals(x, y);
         private protected override int GetHashCode(string s) => Hashing.GetHashCodeOrdinalIgnoreCaseAscii(s.AsSpan());
-        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length % 64))) > 0;
+        private protected override bool CheckLengthQuick(string key) => (_lengthFilter & (1UL << (key.Length & 0x3F))) > 0;
     }
 }