Improve deserialization perf for case-insensitive and missing-property cases

src/libraries/System.Text.Json/src/System/Text/Json/JsonEncodedText.cs

@@ -32,6 +32,15 @@ private JsonEncodedText(byte[] utf8Value)
             _utf8Value = utf8Value;
         }
 
+        private JsonEncodedText(string stringValue, byte[] utf8Value)
+        {
+            Debug.Assert(stringValue != null);
+            Debug.Assert(utf8Value != null);
+
+            _value = stringValue;
+            _utf8Value = utf8Value;
+        }
+
         /// <summary>
         /// Encodes the string text value as a JSON string.
         /// </summary>
@@ -125,6 +134,37 @@ private static JsonEncodedText EncodeHelper(ReadOnlySpan<byte> utf8Value, JavaSc
             }
         }
 
+        /// <summary>
+        /// Internal version that keeps the existing string and byte[] references if there is no escaping required.
+        /// </summary>
+        internal static JsonEncodedText Encode(string stringValue, byte[] utf8Value, JavaScriptEncoder? encoder = null)
+        {
+            Debug.Assert(stringValue.Equals(JsonHelpers.Utf8GetString(utf8Value)));
+
+            if (utf8Value.Length == 0)
+            {
+                return new JsonEncodedText(stringValue, utf8Value);
+            }
+
+            JsonWriterHelper.ValidateValue(utf8Value);
+            return EncodeHelper(stringValue, utf8Value, encoder);
+        }
+
+        private static JsonEncodedText EncodeHelper(string stringValue, byte[] utf8Value, JavaScriptEncoder? encoder)
+        {
+            int idx = JsonWriterHelper.NeedsEscaping(utf8Value, encoder);
+
+            if (idx != -1)
+            {
+                return new JsonEncodedText(GetEscapedString(utf8Value, idx, encoder));
+            }
+            else
+            {
+                // Encoding is not necessary; use the same stringValue and utf8Value references.
+                return new JsonEncodedText(stringValue, utf8Value);
+            }
+        }
+
         private static byte[] GetEscapedString(ReadOnlySpan<byte> utf8Value, int firstEscapeIndexVal, JavaScriptEncoder? encoder)
         {
             Debug.Assert(int.MaxValue / JsonConstants.MaxExpansionFactorWhileEscaping >= utf8Value.Length);

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.Large.cs

@@ -14,11 +14,11 @@ internal sealed class LargeObjectWithParameterizedConstructorConverter<T> : Obje
     {
         protected override bool ReadAndCacheConstructorArgument(ref ReadStack state, ref Utf8JsonReader reader, JsonParameterInfo jsonParameterInfo)
         {
-            bool success = jsonParameterInfo.ReadJson(ref state, ref reader, out object? arg0);
+            bool success = jsonParameterInfo.ReadJson(ref state, ref reader, out object? arg);
 
             if (success)
             {
-                ((object[])state.Current.CtorArgumentState!.Arguments)[jsonParameterInfo.Position] = arg0!;
+                ((object[])state.Current.CtorArgumentState!.Arguments)[jsonParameterInfo.Position] = arg!;
             }
 
             return success;

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.cs

@@ -454,41 +454,19 @@ private bool TryLookupConstructorParameter(
 
             ReadOnlySpan<byte> unescapedPropertyName = JsonSerializer.GetPropertyName(ref state, ref reader, options);
 
-            if (!state.Current.JsonClassInfo.TryGetParameter(unescapedPropertyName, ref state.Current, out jsonParameterInfo))
-            {
-                return false;
-            }
-
-            Debug.Assert(jsonParameterInfo != null);
+            jsonParameterInfo = state.Current.JsonClassInfo.GetParameter(
+                unescapedPropertyName,
+                ref state.Current,
+                out byte[] utf8PropertyName);
 
-            // Increment ConstructorParameterIndex so GetProperty() starts with the next parameter the next time this function is called.
+            // Increment ConstructorParameterIndex so GetParameter() checks the next parameter first when called again.
             state.Current.CtorArgumentState!.ParameterIndex++;
 
-            // Support JsonException.Path.
-            Debug.Assert(
-                jsonParameterInfo.JsonPropertyName == null ||
-                options.PropertyNameCaseInsensitive ||
-                unescapedPropertyName.SequenceEqual(jsonParameterInfo.JsonPropertyName));
-
-            if (jsonParameterInfo.JsonPropertyName == null)
-            {
-                byte[] propertyNameArray = unescapedPropertyName.ToArray();
-                if (options.PropertyNameCaseInsensitive)
-                {
-                    // Each payload can have a different name here; remember the value on the temporary stack.
-                    state.Current.JsonPropertyName = propertyNameArray;
-                }
-                else
-                {
-                    //Prevent future allocs by caching globally on the JsonPropertyInfo which is specific to a Type+PropertyName
-                    // so it will match the incoming payload except when case insensitivity is enabled(which is handled above).
-                    jsonParameterInfo.JsonPropertyName = propertyNameArray;
-                }
-            }
+            // For case insensitive and missing property support of JsonPath, remember the value on the temporary stack.
+            state.Current.JsonPropertyName = utf8PropertyName;
 
             state.Current.CtorArgumentState.JsonParameterInfo = jsonParameterInfo;
-
-            return true;
+            return jsonParameterInfo != null;
         }
 
         internal override bool ConstructorIsParameterized => true;