diff --git a/src/main/scala/millfork/CompilationOptions.scala b/src/main/scala/millfork/CompilationOptions.scala
index bcfcb6b4..be845a12 100644
--- a/src/main/scala/millfork/CompilationOptions.scala
+++ b/src/main/scala/millfork/CompilationOptions.scala
@@ -75,7 +75,7 @@ object CompilationFlag extends Enumeration {
   // compilation options:
   EmitIllegals, EmitCmosOpcodes, DecimalMode, ReadOnlyArrays, PreventJmpIndirectBug,
   // optimization options:
-  DetailedFlowAnalysis, DangerousOptimizations,
+  DetailedFlowAnalysis, DangerousOptimizations, InlineFunctions,
   // memory allocation options
   VariableOverlap,
   // warning options
diff --git a/src/main/scala/millfork/Main.scala b/src/main/scala/millfork/Main.scala
index 21edf0ab..9a5adbd3 100644
--- a/src/main/scala/millfork/Main.scala
+++ b/src/main/scala/millfork/Main.scala
@@ -96,7 +96,7 @@ object Main {
     }
 
     // compile
-    val assembler = new Assembler(env)
+    val assembler = new Assembler(program, env)
     val result = assembler.assemble(callGraph, assemblyOptimizations, options)
     ErrorReporting.assertNoErrors("Codegen failed")
     ErrorReporting.debug(f"Unoptimized code size: ${assembler.unoptimizedCodeSize}%5d B")
@@ -214,6 +214,9 @@ object Main {
       }.description("Optimize code even more.")
       if (i > 3) f.hidden()
     }
+    flag("--inline").action { c =>
+      c.changeFlag(CompilationFlag.InlineFunctions, true)
+    }.description("Inline functions automatically (experimental).")
     flag("--detailed-flow").action { c =>
       c.changeFlag(CompilationFlag.DetailedFlowAnalysis, true)
     }.description("Use detailed flow analysis (experimental).")
diff --git a/src/main/scala/millfork/assembly/AssemblyLine.scala b/src/main/scala/millfork/assembly/AssemblyLine.scala
index 308beca4..a34c3268 100644
--- a/src/main/scala/millfork/assembly/AssemblyLine.scala
+++ b/src/main/scala/millfork/assembly/AssemblyLine.scala
@@ -87,14 +87,16 @@ object OpcodeClasses {
   val ConcernsXAlways = ReadsXAlways | ChangesX
   val ConcernsYAlways = ReadsYAlways | ChangesY
 
-  val ConcernsStack = Set(
+  val ChangesStack = Set(
     PHA, PLA, PHP, PLP,
     PHX, PLX, PHY, PLY,
-    TXS, TSX,
+    TXS,
     JSR, RTS, RTI,
     TAS, LAS,
   )
 
+  val ConcernsStack = ChangesStack + TSX
+
   val ChangesNAndZ = Set(
     ADC, AND, ASL, BIT, CMP, CPX, CPY, DEC, DEX, DEY, EOR, INC, INX, INY, LDA,
     LDX, LDY, LSR, ORA, PLP, ROL, ROR, SBC, TAX, TAY, TXA, TYA,
diff --git a/src/main/scala/millfork/compiler/DecimalBuiltIns.scala b/src/main/scala/millfork/compiler/DecimalBuiltIns.scala
new file mode 100644
index 00000000..3aeec5f0
--- /dev/null
+++ b/src/main/scala/millfork/compiler/DecimalBuiltIns.scala
@@ -0,0 +1,69 @@
+package millfork.compiler
+import millfork.{CompilationFlag, CompilationOptions}
+import millfork.assembly._
+import millfork.env._
+import millfork.node._
+import millfork.assembly.Opcode._
+import millfork.assembly.AddrMode._
+import millfork.error.ErrorReporting
+
+import scala.collection.mutable
+import scala.collection.mutable.ListBuffer
+import millfork.assembly.AssemblyLine
+import millfork.env.{NumericConstant, RegisterVariable, Type}
+import millfork.error.ErrorReporting
+import millfork.node.{Expression, Register}
+
+/**
+  * @author Karol Stasiak
+  */
+object DecimalBuiltIns {
+  def compileByteShiftLeft(ctx: CompilationContext, l: Expression, r: Expression, rotate: Boolean): List[AssemblyLine] = {
+    val b = ctx.env.get[Type]("byte")
+    ctx.env.eval(r) match {
+      case Some(NumericConstant(0, _)) =>
+        Nil
+      case Some(NumericConstant(v, _)) =>
+        val addition = BuiltIns.compileAddition(ctx, List.fill(1<<v)(false -> l), decimal = true)
+        if (rotate) addition.filterNot(_.opcode == CLC) else addition
+      case _ =>
+        ErrorReporting.error("Cannot shift by a non-constant amount")
+        Nil
+    }
+  }
+
+  def compileByteShiftRight(ctx: CompilationContext, l: Expression, r: Expression, rotate: Boolean): List[AssemblyLine] = {
+    val b = ctx.env.get[Type]("byte")
+    ctx.env.eval(r) match {
+      case Some(NumericConstant(0, _)) =>
+        Nil
+      case Some(NumericConstant(1, _)) =>
+        val constantLabel = MlCompiler.nextLabel("c8")
+        val skipHiDigit = MlCompiler.nextLabel("ds")
+        val skipLoDigit = MlCompiler.nextLabel("ds")
+        val bit = if (ctx.options.flags(CompilationFlag.EmitCmosOpcodes)) {
+          AssemblyLine.immediate(BIT, 8)
+        } else {
+          AssemblyLine.absolute(BIT, Label(constantLabel))
+        }
+        List(
+          if (rotate) AssemblyLine.implied(ROR) else AssemblyLine.implied(LSR),
+          AssemblyLine.label(constantLabel),
+          AssemblyLine.implied(PHP),
+          AssemblyLine.relative(BPL, skipHiDigit),
+          AssemblyLine.implied(SEC),
+          AssemblyLine.immediate(SBC, 0x30),
+          AssemblyLine.label(skipHiDigit),
+          bit,
+          AssemblyLine.relative(BPL, skipLoDigit),
+          AssemblyLine.implied(SEC),
+          AssemblyLine.immediate(SBC, 0x3),
+          AssemblyLine.label(skipLoDigit),
+          AssemblyLine.implied(PLP))
+      case _ =>
+        ErrorReporting.error("Cannot shift by a non-constant amount")
+        Nil
+    }
+  }
+
+}
diff --git a/src/main/scala/millfork/output/Assembler.scala b/src/main/scala/millfork/output/Assembler.scala
index 2c2d7123..db51d308 100644
--- a/src/main/scala/millfork/output/Assembler.scala
+++ b/src/main/scala/millfork/output/Assembler.scala
@@ -5,7 +5,7 @@ import millfork.assembly.{AddrMode, AssemblyLine, Opcode}
 import millfork.compiler.{CompilationContext, MlCompiler}
 import millfork.env._
 import millfork.error.ErrorReporting
-import millfork.node.CallGraph
+import millfork.node.{CallGraph, Program}
 import millfork.{CompilationFlag, CompilationOptions, Tarjan}
 
 import scala.collection.mutable
@@ -16,7 +16,7 @@ import scala.collection.mutable
 
 case class AssemblerOutput(code: Array[Byte], asm: Array[String], labels: List[(String, Int)])
 
-class Assembler(private val rootEnv: Environment) {
+class Assembler(private val program: Program, private val rootEnv: Environment) {
 
   var env = rootEnv.allThings
   var unoptimizedCodeSize = 0
@@ -143,11 +143,31 @@ class Assembler(private val rootEnv: Environment) {
 
     val assembly = mutable.ArrayBuffer[String]()
 
+    val potentiallyInlineable: Map[String, Int] =
+      if (options.flags(CompilationFlag.InlineFunctions))
+        InliningCalculator.getPotentiallyInlineableFunctions(program)
+      else Map()
+
+    var inlinedFunctions = Map[String, List[AssemblyLine]]()
     val compiledFunctions = mutable.Map[String, List[AssemblyLine]]()
     callGraph.recommendedCompilationOrder.foreach{ f =>
-      env.maybeGet[NormalFunction](f).foreach( function =>
-        compiledFunctions(f) = compileFunction(function, optimizations, options)
-      )
+      env.maybeGet[NormalFunction](f).foreach{ function =>
+        val code = compileFunction(function, optimizations, options, inlinedFunctions)
+        val strippedCodeForInlining = for {
+          limit <- potentiallyInlineable.get(f)
+          if code.map(_.sizeInBytes).sum <= limit
+          s <- InliningCalculator.codeForInlining(f, code)
+        } yield s
+        strippedCodeForInlining match {
+          case Some(c) =>
+            ErrorReporting.debug("Inlining " + f, function.position)
+            inlinedFunctions += f -> c
+            compiledFunctions(f) = Nil
+          case None =>
+            compiledFunctions(f) = code
+            optimizedCodeSize += code.map(_.sizeInBytes).sum
+        }
+      }
     }
 
     env.allPreallocatables.foreach {
@@ -249,14 +269,20 @@ class Assembler(private val rootEnv: Environment) {
     AssemblerOutput(platform.outputPackager.packageOutput(mem, 0), assembly.toArray, labelMap.toList)
   }
 
-  private def compileFunction(f: NormalFunction, optimizations: Seq[AssemblyOptimization], options: CompilationOptions) :List[AssemblyLine] = {
+  private def compileFunction(f: NormalFunction, optimizations: Seq[AssemblyOptimization], options: CompilationOptions, inlinedFunctions: Map[String, List[AssemblyLine]]) :List[AssemblyLine] = {
     ErrorReporting.debug("Compiling: " + f.name, f.position)
-    val unoptimized = MlCompiler.compile(CompilationContext(env = f.environment, function = f, extraStackOffset = 0, options = options)).linearize
+    val unoptimized =
+      MlCompiler.compile(CompilationContext(env = f.environment, function = f, extraStackOffset = 0, options = options)).linearize.flatMap{
+      case AssemblyLine(Opcode.JSR, _, p, true) if inlinedFunctions.contains(p.toString) =>
+        inlinedFunctions(p.toString)
+      case AssemblyLine(Opcode.JMP, AddrMode.Absolute, p, true) if inlinedFunctions.contains(p.toString) =>
+        inlinedFunctions(p.toString) :+ AssemblyLine.implied(Opcode.RTS)
+      case x => List(x)
+    }
     unoptimizedCodeSize += unoptimized.map(_.sizeInBytes).sum
     val code = optimizations.foldLeft(unoptimized) { (c, opt) =>
       opt.optimize(f, c, options)
     }
-    optimizedCodeSize += code.map(_.sizeInBytes).sum
     code
   }
 
diff --git a/src/main/scala/millfork/output/InliningCalculator.scala b/src/main/scala/millfork/output/InliningCalculator.scala
new file mode 100644
index 00000000..5fecf611
--- /dev/null
+++ b/src/main/scala/millfork/output/InliningCalculator.scala
@@ -0,0 +1,75 @@
+package millfork.output
+
+import millfork.assembly.{AssemblyLine, Opcode, OpcodeClasses}
+import millfork.assembly.Opcode._
+import millfork.env._
+import millfork.node._
+
+import scala.collection.mutable
+
+/**
+  * @author Karol Stasiak
+  */
+object InliningCalculator {
+
+  private val sizes = Seq(30, 30, 8, 6, 5, 5, 4)
+
+  def getPotentiallyInlineableFunctions(program: Program): Map[String, Int] = {
+    val callCount = mutable.Map[String, Int]().withDefaultValue(0)
+    val allFunctions = mutable.Set[String]()
+    val badFunctions = mutable.Set[String]()
+    getAllCalledFunctions(program.declarations).foreach{
+      case (name, true) => badFunctions += name
+      case (name, false) => callCount(name) += 1
+    }
+    program.declarations.foreach{
+      case f:FunctionDeclarationStatement =>
+        allFunctions += f.name
+        if (f.inlined) badFunctions += f.name
+        if (f.address.isDefined) badFunctions += f.name
+        if (f.interrupt) badFunctions += f.name
+        if (f.reentrant) badFunctions += f.name
+        if (f.name == "main") badFunctions += f.name
+      case _ =>
+    }
+    allFunctions --= badFunctions
+    allFunctions.map(f => f -> sizes(callCount(f) min (sizes.size - 1))).toMap
+  }
+
+  private def getAllCalledFunctions(expressions: List[Node]): List[(String, Boolean)] = expressions.flatMap {
+    case s: VariableDeclarationStatement => getAllCalledFunctions(s.address.toList) ++ getAllCalledFunctions(s.initialValue.toList)
+    case s: ArrayDeclarationStatement => getAllCalledFunctions(s.address.toList) ++ getAllCalledFunctions(s.elements.getOrElse(Nil))
+    case s: FunctionDeclarationStatement => getAllCalledFunctions(s.address.toList) ++ getAllCalledFunctions(s.statements.getOrElse(Nil))
+    case Assignment(VariableExpression(_), expr) => getAllCalledFunctions(expr :: Nil)
+    case AssemblyStatement(JSR, _, VariableExpression(name), true) => (name -> false) :: Nil
+    case s: Statement => getAllCalledFunctions(s.getAllExpressions)
+    case s: VariableExpression => Set(
+          s.name,
+          s.name.stripSuffix(".addr"),
+          s.name.stripSuffix(".hi"),
+          s.name.stripSuffix(".lo"),
+          s.name.stripSuffix(".addr.lo"),
+          s.name.stripSuffix(".addr.hi")).toList.map(_ -> true)
+    case s: LiteralExpression => Nil
+    case HalfWordExpression(param, _) => getAllCalledFunctions(param :: Nil)
+    case SumExpression(xs, _) => getAllCalledFunctions(xs.map(_._2))
+    case FunctionCallExpression(name, xs) => (name -> false) :: getAllCalledFunctions(xs)
+    case IndexedExpression(arr, index) => (arr -> true) :: getAllCalledFunctions(List(index))
+    case SeparateBytesExpression(h, l) => getAllCalledFunctions(List(h, l))
+    case _ => Nil
+  }
+
+  private val badOpcodes =
+    Set(RTI, RTS, JSR, JMP, LABEL, BRK) ++
+      OpcodeClasses.ShortBranching ++
+      OpcodeClasses.ChangesStack
+
+  def codeForInlining(fname: String, code: List[AssemblyLine]): Option[List[AssemblyLine]] = {
+    if (code.isEmpty) return None
+    if (code.last.opcode != RTS) return None
+    var result = code.init
+    if (result.head.opcode == LABEL && result.head.parameter == Label(fname).toAddress) result = result.tail
+    if (result.exists(l => badOpcodes(l.opcode))) return None
+    Some(result)
+  }
+}
diff --git a/src/test/scala/millfork/test/emu/EmuBenchmarkRun.scala b/src/test/scala/millfork/test/emu/EmuBenchmarkRun.scala
index e0dea4ca..bf0b663d 100644
--- a/src/test/scala/millfork/test/emu/EmuBenchmarkRun.scala
+++ b/src/test/scala/millfork/test/emu/EmuBenchmarkRun.scala
@@ -9,12 +9,17 @@ object EmuBenchmarkRun {
   def apply(source: String)(verifier: MemoryBank => Unit) = {
     val (Timings(t0, _), m0) = EmuUnoptimizedRun.apply2(source)
     val (Timings(t1, _), m1) = EmuOptimizedRun.apply2(source)
+    val (Timings(t2, _), m2) = EmuOptimizedInlinedRun.apply2(source)
     println(f"Before optimization: $t0%7d")
     println(f"After optimization:  $t1%7d")
+    println(f"After inlining:      $t2%7d")
     println(f"Gain:               ${(100L * (t0 - t1) / t0.toDouble).round}%7d%%")
+    println(f"Gain with inlining: ${(100L * (t0 - t2) / t0.toDouble).round}%7d%%")
     println(f"Running unoptimized")
     verifier(m0)
     println(f"Running optimized")
     verifier(m1)
+    println(f"Running optimized inlined")
+    verifier(m2)
   }
 }
diff --git a/src/test/scala/millfork/test/emu/EmuOptimizedInlinedRun.scala b/src/test/scala/millfork/test/emu/EmuOptimizedInlinedRun.scala
new file mode 100644
index 00000000..8506cfb0
--- /dev/null
+++ b/src/test/scala/millfork/test/emu/EmuOptimizedInlinedRun.scala
@@ -0,0 +1,15 @@
+package millfork.test.emu
+
+import millfork.{Cpu, OptimizationPresets}
+
+/**
+  * @author Karol Stasiak
+  */
+object EmuOptimizedInlinedRun extends EmuRun(
+  Cpu.StrictMos,
+  OptimizationPresets.NodeOpt,
+  OptimizationPresets.AssOpt ++ OptimizationPresets.Good ++ OptimizationPresets.Good ++ OptimizationPresets.Good,
+  false)
+
+
+
diff --git a/src/test/scala/millfork/test/emu/EmuRun.scala b/src/test/scala/millfork/test/emu/EmuRun.scala
index 19d79c82..9599931d 100644
--- a/src/test/scala/millfork/test/emu/EmuRun.scala
+++ b/src/test/scala/millfork/test/emu/EmuRun.scala
@@ -28,6 +28,8 @@ class EmuRun(cpu: millfork.Cpu.Value, nodeOptimizations: List[NodeOptimization],
 
   def emitIllegals = false
 
+  def inline = false
+
   private val timingNmos = Array[Int](
     7, 6, 0, 8, 3, 3, 5, 5, 3, 2, 2, 2, 4, 4, 6, 6,
     2, 5, 0, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,
@@ -91,6 +93,7 @@ class EmuRun(cpu: millfork.Cpu.Value, nodeOptimizations: List[NodeOptimization],
     val options = new CompilationOptions(platform, Map(
       CompilationFlag.EmitIllegals -> this.emitIllegals,
       CompilationFlag.DetailedFlowAnalysis -> quantum,
+      CompilationFlag.InlineFunctions -> this.inline,
     ))
     ErrorReporting.hasErrors = false
     ErrorReporting.verbosity = 999
@@ -107,42 +110,31 @@ class EmuRun(cpu: millfork.Cpu.Value, nodeOptimizations: List[NodeOptimization],
         env.collectDeclarations(program, options)
 
         val hasOptimizations = assemblyOptimizations.nonEmpty
-        var optimizedSize = 0L
         var unoptimizedSize = 0L
         // print asm
         env.allPreallocatables.foreach {
           case f: NormalFunction =>
             val result = MlCompiler.compile(CompilationContext(f.environment, f, 0, options))
             val unoptimized = result.linearize
-            if (hasOptimizations) {
-              val optimized = assemblyOptimizations.foldLeft(unoptimized) { (c, opt) =>
-                opt.optimize(f, c, options)
-              }
-              println("Unoptimized:")
-              unoptimized.filter(_.isPrintable).foreach(println(_))
-              println("Optimized:")
-              optimized.filter(_.isPrintable).foreach(println(_))
-              unoptimizedSize += unoptimized.map(_.sizeInBytes).sum
-              optimizedSize += optimized.map(_.sizeInBytes).sum
-            } else {
-              unoptimized.filter(_.isPrintable).foreach(println(_))
-              unoptimizedSize += unoptimized.map(_.sizeInBytes).sum
-              optimizedSize += unoptimized.map(_.sizeInBytes).sum
-            }
+            unoptimizedSize += unoptimized.map(_.sizeInBytes).sum
           case d: InitializedArray =>
-            println(d.name)
-            d.contents.foreach(c => println("    !byte " + c))
             unoptimizedSize += d.contents.length
-            optimizedSize += d.contents.length
           case d: InitializedMemoryVariable =>
-            println(d.name)
-            0.until(d.typ.size).foreach(c => println("    !byte " + d.initialValue.subbyte(c)))
             unoptimizedSize += d.typ.size
-            optimizedSize += d.typ.size
         }
 
         ErrorReporting.assertNoErrors("Compile failed")
 
+
+        // compile
+        val assembler = new Assembler(program, env)
+        val output = assembler.assemble(callGraph, assemblyOptimizations, options)
+        println(";;; compiled: -----------------")
+        output.asm.takeWhile(s => !(s.startsWith(".") && s.contains("= $"))).foreach(println)
+        println(";;; ---------------------------")
+        assembler.labelMap.foreach { case (l, addr) => println(f"$l%-15s $$$addr%04x") }
+
+        val optimizedSize = assembler.mem.banks(0).occupied.count(identity).toLong
         if (unoptimizedSize == optimizedSize) {
           println(f"Size:             $unoptimizedSize%5d B")
         } else {
@@ -151,11 +143,6 @@ class EmuRun(cpu: millfork.Cpu.Value, nodeOptimizations: List[NodeOptimization],
           println(f"Gain:              ${(100L * (unoptimizedSize - optimizedSize) / unoptimizedSize.toDouble).round}%5d%%")
         }
 
-        // compile
-        val assembler = new Assembler(env)
-        assembler.assemble(callGraph, assemblyOptimizations, options)
-        assembler.labelMap.foreach { case (l, addr) => println(f"$l%-15s $$$addr%04x") }
-
         ErrorReporting.assertNoErrors("Code generation failed")
 
         val memoryBank = assembler.mem.banks(0)
diff --git a/src/test/scala/millfork/test/emu/EmuSuperOptimizedInliningRun.scala b/src/test/scala/millfork/test/emu/EmuSuperOptimizedInliningRun.scala
new file mode 100644
index 00000000..98139190
--- /dev/null
+++ b/src/test/scala/millfork/test/emu/EmuSuperOptimizedInliningRun.scala
@@ -0,0 +1,18 @@
+package millfork.test.emu
+
+import millfork.assembly.opt.SuperOptimizer
+import millfork.{Cpu, OptimizationPresets}
+
+/**
+  * @author Karol Stasiak
+  */
+object EmuSuperQuantumOptimizedInliningRun extends EmuRun(
+  Cpu.StrictMos,
+  OptimizationPresets.NodeOpt,
+  List(SuperOptimizer),
+  true) {
+  override def inline = true
+}
+
+
+
diff --git a/src/test/scala/millfork/test/emu/EmuSuperoptimizedRun.scala b/src/test/scala/millfork/test/emu/EmuSuperoptimizedRun.scala
index 30be3c0d..f39d8c24 100644
--- a/src/test/scala/millfork/test/emu/EmuSuperoptimizedRun.scala
+++ b/src/test/scala/millfork/test/emu/EmuSuperoptimizedRun.scala
@@ -6,7 +6,6 @@ import millfork.{Cpu, OptimizationPresets}
 /**
   * @author Karol Stasiak
   */
-// TODO : it doesn't work
 object EmuSuperOptimizedRun extends EmuRun(
   Cpu.StrictMos,
   OptimizationPresets.NodeOpt,
diff --git a/src/test/scala/millfork/test/emu/EmuUltraBenchmarkRun.scala b/src/test/scala/millfork/test/emu/EmuUltraBenchmarkRun.scala
index 008b7dcc..40e0bbe6 100644
--- a/src/test/scala/millfork/test/emu/EmuUltraBenchmarkRun.scala
+++ b/src/test/scala/millfork/test/emu/EmuUltraBenchmarkRun.scala
@@ -12,15 +12,18 @@ object EmuUltraBenchmarkRun {
     val (Timings(t2, _), m2) = EmuSuperOptimizedRun.apply2(source)
     val (Timings(t3, _), m3) = EmuQuantumOptimizedRun.apply2(source)
     val (Timings(t4, _), m4) = EmuSuperQuantumOptimizedRun.apply2(source)
+    val (Timings(t5, _), m5) = EmuSuperQuantumOptimizedInliningRun.apply2(source)
     println(f"Before optimization: $t0%7d")
     println(f"After optimization:  $t1%7d")
     println(f"After superopt.:     $t2%7d")
     println(f"After quantum:       $t3%7d")
     println(f"After superquantum:  $t4%7d")
+    println(f"After inlining:      $t5%7d")
     println(f"Gain:               ${(100L*(t0-t1)/t0.toDouble).round}%7d%%")
     println(f"Superopt. gain:     ${(100L*(t0-t2)/t0.toDouble).round}%7d%%")
     println(f"Quantum gain:       ${(100L*(t0-t3)/t0.toDouble).round}%7d%%")
     println(f"Super quantum gain: ${(100L*(t0-t4)/t0.toDouble).round}%7d%%")
+    println(f"SQ+inlining gain:   ${(100L*(t0-t5)/t0.toDouble).round}%7d%%")
     println(f"Running unoptimized")
     verifier(m0)
     println(f"Running optimized")
@@ -31,5 +34,7 @@ object EmuUltraBenchmarkRun {
     verifier(m3)
     println(f"Running superquantum optimized")
     verifier(m4)
+    println(f"Running superquantum optimized inlined")
+    verifier(m5)
   }
 }