diff --git a/compiler/src/prog8/optimizer/CallGraph.kt b/compiler/src/prog8/optimizer/CallGraph.kt
index 1c02482ed..4b533d7ff 100644
--- a/compiler/src/prog8/optimizer/CallGraph.kt
+++ b/compiler/src/prog8/optimizer/CallGraph.kt
@@ -3,7 +3,9 @@ package prog8.optimizer
 import prog8.ast.Module
 import prog8.ast.Node
 import prog8.ast.Program
+import prog8.ast.base.DataType
 import prog8.ast.base.Position
+import prog8.ast.base.VarDeclType
 import prog8.ast.expressions.AddressOf
 import prog8.ast.expressions.FunctionCall
 import prog8.ast.expressions.IdentifierReference
@@ -18,7 +20,7 @@ class CallGraph(private val program: Program) : IAstVisitor {
     val importedBy = mutableMapOf<Module, Set<Module>>().withDefault { setOf() }
     val calls = mutableMapOf<Subroutine, Set<Subroutine>>().withDefault { setOf() }
     val calledBy = mutableMapOf<Subroutine, Set<Node>>().withDefault { setOf() }
-    private val allIdentifiers = mutableSetOf<IdentifierReference>()
+    private val allIdentifiersAndTargets = mutableMapOf<Pair<IdentifierReference, Position>, Statement>()
 
     init {
         visit(program)
@@ -35,9 +37,9 @@ class CallGraph(private val program: Program) : IAstVisitor {
         val blocksFromLibraries = program.allBlocks().filter { it.isInLibrary }
         val used = mutableSetOf<Block>()
 
-        allIdentifiers.forEach {
-            if(it.definingBlock() in blocksFromSubroutines) {
-                val target = it.targetStatement(program)!!.definingBlock()
+        allIdentifiersAndTargets.forEach {
+            if(it.key.first.definingBlock() in blocksFromSubroutines) {
+                val target = it.value.definingBlock()
                 used.add(target)
             }
         }
@@ -46,7 +48,7 @@ class CallGraph(private val program: Program) : IAstVisitor {
     }
 
     private val usedModules: Set<Module> by lazy {
-        program.modules.toSet() // TODO
+        usedBlocks.map { it.definingModule() }.toSet()
     }
 
     override fun visit(directive: Directive) {
@@ -105,7 +107,7 @@ class CallGraph(private val program: Program) : IAstVisitor {
     }
 
     override fun visit(identifier: IdentifierReference) {
-        allIdentifiers.add(identifier)
+        allIdentifiersAndTargets[Pair(identifier, identifier.position)] = identifier.targetStatement(program)!!
     }
 
     fun checkRecursiveCalls(errors: IErrorReporter) {
@@ -166,11 +168,24 @@ class CallGraph(private val program: Program) : IAstVisitor {
     fun unused(block: Block) = block !in usedBlocks
 
     fun unused(decl: VarDecl): Boolean {
-        return false    // TODO implement unused check for vardecls, also check inline asm
+        if(decl.type!=VarDeclType.VAR || decl.datatype==DataType.STRUCT || decl.autogeneratedDontRemove || decl.parent is StructDecl)
+            return false
+
+        if(decl.definingBlock() !in usedBlocks)
+            return false
+
+        // TODO also check inline asm for references to the var
+        val allReferencedVardecls = allIdentifiersAndTargets.filter { it.value is VarDecl }.map { it.value }.toSet()
+
+        return decl !in allReferencedVardecls
     }
 
     fun unused(struct: StructDecl): Boolean {
-        return false    // TODO implement unused check for struct decls, also check inline asm
+        if(struct.definingBlock() !in usedBlocks)
+            return false
+
+        // TODO implement unused check for struct decls, also check inline asm
+        return false
     }
 
     inline fun unused(label: Label) = false   // just always output labels
diff --git a/compiler/src/prog8/optimizer/UnusedCodeRemover.kt b/compiler/src/prog8/optimizer/UnusedCodeRemover.kt
index c82dfdb84..c8dc5ac4b 100644
--- a/compiler/src/prog8/optimizer/UnusedCodeRemover.kt
+++ b/compiler/src/prog8/optimizer/UnusedCodeRemover.kt
@@ -105,8 +105,8 @@ internal class UnusedCodeRemover(private val program: Program,
 
     override fun after(decl: VarDecl, parent: Node): Iterable<IAstModification> {
         val forceOutput = "force_output" in decl.definingBlock().options()
-        if(!forceOutput && callgraph.unused(decl)) {
-            if(decl.type == VarDeclType.VAR)
+        if(!forceOutput && !decl.autogeneratedDontRemove && callgraph.unused(decl)) {
+            if(decl.type == VarDeclType.VAR && !decl.definingBlock().isInLibrary)
                 errors.warn("removing unused variable '${decl.name}'", decl.position)
 
             return listOf(IAstModification.Remove(decl, decl.definingScope()))
diff --git a/compilerAst/src/prog8/ast/expressions/AstExpressions.kt b/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
index 39604f8c2..910d60096 100644
--- a/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
+++ b/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
@@ -727,7 +727,7 @@ data class IdentifierReference(val nameInSource: List<String>, override val posi
     fun targetVarDecl(program: Program): VarDecl? = targetStatement(program) as? VarDecl
     fun targetSubroutine(program: Program): Subroutine? = targetStatement(program) as? Subroutine
 
-    override fun equals(other: Any?) = other is IdentifierReference && other.nameInSource==nameInSource
+    override fun equals(other: Any?) = other is IdentifierReference && other.nameInSource==nameInSource     // NOTE: only compare by the name, not the position!
     override fun hashCode() = nameInSource.hashCode()
 
     override fun linkParents(parent: Node) {
diff --git a/compilerAst/src/prog8/ast/walk/AstWalker.kt b/compilerAst/src/prog8/ast/walk/AstWalker.kt
index aa05b7c57..41db120d5 100644
--- a/compilerAst/src/prog8/ast/walk/AstWalker.kt
+++ b/compilerAst/src/prog8/ast/walk/AstWalker.kt
@@ -160,7 +160,6 @@ abstract class AstWalker {
     open fun after(whileLoop: WhileLoop, parent: Node): Iterable<IAstModification> = noModifications
 
     protected val modifications = mutableListOf<Triple<IAstModification, Node, Node>>()
-    // private val modificationsReplacedNodes = mutableSetOf<Pair<Node, Position>>()
 
     private fun track(mods: Iterable<IAstModification>, node: Node, parent: Node) {
         for (it in mods) {
@@ -176,12 +175,23 @@ abstract class AstWalker {
     }
 
     fun applyModifications(): Int {
+        // check if there are double removes, keep only the last one
+        val removals = modifications.filter { it.first is IAstModification.Remove }
+        if(removals.size>0) {
+            val doubles = removals.groupBy { (it.first as IAstModification.Remove).node }.filter { it.value.size>1 }
+            doubles.forEach {
+                for(doubleRemove in it.value.dropLast(1)) {
+                    if(!modifications.removeIf { mod-> mod.first === doubleRemove.first })
+                        throw FatalAstException("ast remove problem")
+                }
+            }
+        }
+
         modifications.forEach {
             it.first.perform()
         }
         val amount = modifications.size
         modifications.clear()
-//        modificationsReplacedNodes.clear()
         return amount
     }