Optimize Dictionary.FindValue for constant keys (no constant folding)

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Dictionary.cs

@@ -409,7 +409,8 @@ internal ref TValue FindValue(TKey key)
                 if (typeof(TKey).IsValueType && // comparer can only be null for value types; enable JIT to eliminate entire if block for ref types
                     comparer == null)
                 {
-                    uint hashCode = (uint)key.GetHashCode();
+                    // TODO: Replace with just key.GetHashCode once https://github.com/dotnet/runtime/issues/117521 is resolved.
+                    uint hashCode = (uint)EqualityComparer<TKey>.Default.GetHashCode(key);
                     int i = GetBucket(hashCode);
                     Entry[]? entries = _entries;
                     uint collisionCount = 0;

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs

@@ -112,7 +112,7 @@ internal OrdinalIgnoreCaseComparer(IEqualityComparer<string?> wrappedComparer) :
             {
             }
 
-            public override bool Equals(string? x, string? y) => string.EqualsOrdinalIgnoreCase(x, y);
+            public override bool Equals(string? x, string? y) => string.Equals(x, y, StringComparison.OrdinalIgnoreCase);
 
             public override int GetHashCode(string? obj)
             {

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/RandomizedStringEqualityComparer.cs

@@ -102,7 +102,7 @@ internal OrdinalIgnoreCaseComparer(IEqualityComparer<string?> wrappedComparer)
             string IAlternateEqualityComparer<ReadOnlySpan<char>, string?>.Create(ReadOnlySpan<char> span) =>
                 span.ToString();
 
-            public override bool Equals(string? x, string? y) => string.EqualsOrdinalIgnoreCase(x, y);
+            public override bool Equals(string? x, string? y) => string.Equals(x, y, StringComparison.OrdinalIgnoreCase);
 
             bool IAlternateEqualityComparer<ReadOnlySpan<char>, string?>.Equals(ReadOnlySpan<char> alternate, string? other)
             {

src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs

@@ -46,26 +46,6 @@ ref Unsafe.Add(ref strA.GetRawStringData(), (nint)(uint)indexA /* force zero-ext
                 ref Unsafe.Add(ref strB.GetRawStringData(), (nint)(uint)indexB /* force zero-extension */), countB);
         }
 
-        internal static bool EqualsOrdinalIgnoreCase(string? strA, string? strB)
-        {
-            if (ReferenceEquals(strA, strB))
-            {
-                return true;
-            }
-
-            if (strA is null || strB is null)
-            {
-                return false;
-            }
-
-            if (strA.Length != strB.Length)
-            {
-                return false;
-            }
-
-            return EqualsOrdinalIgnoreCaseNoLengthCheck(strA, strB);
-        }
-
         private static bool EqualsOrdinalIgnoreCaseNoLengthCheck(string strA, string strB)
         {
             Debug.Assert(strA.Length == strB.Length);