diff --git a/compiler/src/prog8/ast/AstToplevel.kt b/compiler/src/prog8/ast/AstToplevel.kt
index 46d8af973..d74650044 100644
--- a/compiler/src/prog8/ast/AstToplevel.kt
+++ b/compiler/src/prog8/ast/AstToplevel.kt
@@ -54,6 +54,7 @@ interface INameScope {
     fun linkParents(parent: Node)
 
     fun subScopes(): Map<String, INameScope> {
+        // TODO PERFORMANCE: this is called very often and is relatively expensive. Optimize this.
         val subscopes = mutableMapOf<String, INameScope>()
         for(stmt in statements) {
             when(stmt) {
@@ -126,7 +127,7 @@ interface INameScope {
             for(module in localContext.definingModule().program.modules) {
                 var scope: INameScope? = module
                 for(name in scopedName.dropLast(1)) {
-                    scope = scope?.subScopes()?.get(name)
+                    scope = scope?.subScopes()?.get(name)           // TODO PERFORMANCE: EXPENSIVE! (creates new map every call) OPTIMIZE.
                     if(scope==null)
                         break
                 }
diff --git a/compiler/src/prog8/optimizer/CallGraph.kt b/compiler/src/prog8/optimizer/CallGraph.kt
index ad497e61f..40bcd5c3f 100644
--- a/compiler/src/prog8/optimizer/CallGraph.kt
+++ b/compiler/src/prog8/optimizer/CallGraph.kt
@@ -29,7 +29,7 @@ class CallGraph(private val program: Program) : IAstVisitor {
     val subroutinesCalling = mutableMapOf<INameScope, List<Subroutine>>().withDefault { mutableListOf() }
     val subroutinesCalledBy = mutableMapOf<Subroutine, List<Node>>().withDefault { mutableListOf() }
 
-    // TODO  add dataflow graph: what statements use what variables
+    // TODO  add dataflow graph: what statements use what variables - can be used to eliminate unused vars
     val usedSymbols = mutableSetOf<Statement>()
 
     init {
diff --git a/compiler/src/prog8/optimizer/StatementOptimizer.kt b/compiler/src/prog8/optimizer/StatementOptimizer.kt
index 5b283c333..9c2c25bb5 100644
--- a/compiler/src/prog8/optimizer/StatementOptimizer.kt
+++ b/compiler/src/prog8/optimizer/StatementOptimizer.kt
@@ -24,7 +24,7 @@ internal class StatementOptimizer(private val program: Program,
         private set
 
     private val pureBuiltinFunctions = BuiltinFunctions.filter { it.value.pure }
-    private val callgraph = CallGraph(program)
+    private val callgraph = CallGraph(program)      // TODO PERFORMANCE: it is expensive to create this every round
     private val vardeclsToRemove = mutableListOf<VarDecl>()
 
     override fun visit(program: Program) {
@@ -37,6 +37,7 @@ internal class StatementOptimizer(private val program: Program,
     }
 
     private fun removeUnusedCode(callgraph: CallGraph) {
+        // TODO PERFORMANCE: expensive code (because of callgraph) OPTIMIZE THIS: only run once separately ?
         // remove all subroutines that aren't called, or are empty
         val removeSubroutines = mutableSetOf<Subroutine>()
         val entrypoint = program.entrypoint()