PR Feedback.

src/Compilers/Core/Portable/MetadataReader/PEModule.cs

@@ -1140,6 +1140,9 @@ internal bool HasIsByRefLikeAttribute(EntityHandle token)
             IAttributeNamedArgumentDecoder attributeArgumentDecoder,
             Func<string, TypedConstant, bool, (bool IsCallConvs, ImmutableHashSet<INamedTypeSymbolInternal>? CallConvs)> unmanagedCallersOnlyDecoder)
         {
+            // We don't want to load all attributes and their public data just to answer whether a PEMethodSymbol has an UnmanagedCallersOnly
+            // attached. It would create unnecessary memory pressure that isn't going to be needed 99% of the time, so we just crack this 1
+            // attribute.
             AttributeInfo info = FindTargetAttribute(token, AttributeDescription.UnmanagedCallersOnlyAttribute);
             if (!info.HasValue || info.SignatureIndex != 0 || !TryGetAttributeReader(info.Handle, out BlobReader sigReader))
             {

src/Compilers/Core/Portable/Symbols/Attributes/UnmanagedCallersOnlyAttributeData.cs

@@ -23,7 +23,7 @@ internal static UnmanagedCallersOnlyAttributeData Create(ImmutableHashSet<INamed
             => callingConventionTypes switch
             {
                 null or { IsEmpty: true } => PlatformDefault,
-                _ => new UnmanagedCallersOnlyAttributeData(callingConventionTypes ?? ImmutableHashSet<INamedTypeSymbolInternal>.Empty)
+                _ => new UnmanagedCallersOnlyAttributeData(callingConventionTypes)
             };
 
         public readonly ImmutableHashSet<INamedTypeSymbolInternal> CallingConventionTypes;