Remove some allocations related to logging configuration

src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Reflection;
 
@@ -13,16 +14,19 @@ internal static class ProviderAliasUtilities
 
         internal static string GetAlias(Type providerType)
         {
-            foreach (CustomAttributeData attributeData in CustomAttributeData.GetCustomAttributes(providerType))
+            IList<CustomAttributeData> attributes = CustomAttributeData.GetCustomAttributes(providerType);
+
+            for (int i = 0; i < attributes.Count; i++)
             {
-                if (attributeData.AttributeType.FullName == AliasAttibuteTypeFullName)
+                CustomAttributeData attributeData = attributes[i];
+                if (attributeData.AttributeType.FullName == AliasAttibuteTypeFullName &&
+                    attributeData.ConstructorArguments.Count > 0)
                 {
-                    foreach (CustomAttributeTypedArgument arg in attributeData.ConstructorArguments)
-                    {
-                        Debug.Assert(arg.ArgumentType == typeof(string));
+                    CustomAttributeTypedArgument arg = attributeData.ConstructorArguments[0];
+
+                    Debug.Assert(arg.ArgumentType == typeof(string));
 
-                        return arg.Value?.ToString();
-                    }
+                    return arg.Value?.ToString();
                 }
             }
 

src/libraries/Microsoft.Extensions.Logging/src/LoggerFilterOptions.cs

@@ -28,6 +28,9 @@ public LoggerFilterOptions() { }
         /// <summary>
         /// Gets the collection of <see cref="LoggerFilterRule"/> used for filtering log messages.
         /// </summary>
-        public IList<LoggerFilterRule> Rules { get; } = new List<LoggerFilterRule>();
+        public IList<LoggerFilterRule> Rules => RulesInternal;
+
+        // Concrete representation of the rule list
+        internal List<LoggerFilterRule> RulesInternal { get; } = new List<LoggerFilterRule>();
     }
 }

src/libraries/Microsoft.Extensions.Logging/src/LoggerRuleSelector.cs

@@ -22,7 +22,7 @@ public static void Select(LoggerFilterOptions options, Type providerType, string
 
             string providerAlias = ProviderAliasUtilities.GetAlias(providerType);
             LoggerFilterRule current = null;
-            foreach (LoggerFilterRule rule in options.Rules)
+            foreach (LoggerFilterRule rule in options.RulesInternal)
             {
                 if (IsBetter(rule, current, providerType.FullName, category)
                     || (!string.IsNullOrEmpty(providerAlias) && IsBetter(rule, current, providerAlias, category)))