Improvements to performance of mono_wasm_get_assembly_exports

Author: kg

src/libraries/System.Runtime.InteropServices.JavaScript/gen/JSImportGenerator/JSExportGenerator.cs

@@ -241,8 +241,9 @@ private static NamespaceDeclarationSyntax GenerateRegSource(
                             .WithModifiers(TokenList(new[] { Token(SyntaxKind.StaticKeyword) }))
                             .WithBody(Block(registerStatements));
 
-            // when we are running code generated by .NET8 on .NET7 runtime we need to auto initialize the assembly, because .NET7 doesn't call the registration from JS
-            // this also keeps the code protected from trimming
+            // HACK: protect the code from trimming by putting it behind a comparison we know
+            //  will always evaluate to false at runtime, but the linker can't see through at
+            //  build time. It seems there's no attribute to block trimming of a method?
             MemberDeclarationSyntax initializerMethod = MethodDeclaration(PredefinedType(Token(SyntaxKind.VoidKeyword)), Identifier(selfInitName))
                             .WithAttributeLists(List(new[]{
                                     AttributeList(SingletonSeparatedList(Attribute(IdentifierName(Constants.ModuleInitializerAttributeGlobal)))),
@@ -253,8 +254,8 @@ private static NamespaceDeclarationSyntax GenerateRegSource(
                             }))
                             .WithBody(Block(
                                 IfStatement(BinaryExpression(SyntaxKind.EqualsExpression,
-                                    IdentifierName("Environment.Version.Major"),
-                                    LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(7))),
+                                    IdentifierName("System.Runtime.InteropServices.JavaScript.JSHost.GlobalThis"),
+                                    LiteralExpression(SyntaxKind.NullLiteralExpression)),
                                     Block(SingletonList<StatementSyntax>(
                                         ExpressionStatement(InvocationExpression(IdentifierName(initializerName))))))));
 

src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSHostImplementation.cs

@@ -333,7 +333,7 @@ public static (string assemblyName, string nameSpace, string shortClassName, str
 
             var nameSpace = "";
             var shortClassName = className;
-            var idx = fqn.LastIndexOf(".");
+            var idx = fqn.LastIndexOf('.');
             if (idx != -1)
             {
                 nameSpace = fqn.Substring(0, idx);