6502: Fix fatal failure when considering undocumented optimizations (fixes #38)

src/main/scala/millfork/assembly/mos/opt/UndocumentedOptimizations.scala

@@ -134,7 +134,7 @@ object UndocumentedOptimizations {
     (Elidable & HasOpcode(INX) & DoesntMatterWhatItDoesWith(State.A)).+.captureLength(0) ~
       Where(_.get[Int](0) > 2) ~~> ((_, ctx) => List(
       AssemblyLine.implied(TXA),
-      AssemblyLine.immediate(SBX, Constant.Zero - ctx.get[Constant](0)),
+      AssemblyLine.immediate(SBX, Constant.Zero - ctx.get[Int](0)),
     )),
     HasOpcode(TXA) ~
       (Elidable & HasOpcode(CLC)).? ~

src/test/scala/millfork/test/IllegalSuite.scala

@@ -261,4 +261,27 @@ class IllegalSuite extends FunSuite with Matchers {
       """.stripMargin)
     m.readLong(0xc000) should equal(1)
   }
+
+  test("Test issue #38") {
+    val m = EmuUndocumentedRun(
+      """
+        |array(byte) input [16] @ $c300
+        |const byte COUNT = 16
+        |byte output @$c000
+        |void main() {
+        |    inner()
+        |}
+        |
+        |void inner() {
+        |    byte j
+        |    for j,0,until,COUNT {
+        |        if input[j] == 0 {
+        |            continue
+        |        }
+        |        //output += 1
+        |    }
+        |}
+        |
+        |""".stripMargin)
+  }
 }

src/test/scala/millfork/test/emu/EmuUndocumentedRun.scala

@@ -13,6 +13,10 @@ object EmuUndocumentedRun extends EmuRun(
     UndocumentedOptimizations.All ++
     OptimizationPresets.Good ++ LaterOptimizations.Nmos ++
     UndocumentedOptimizations.All ++
+    OptimizationPresets.AssOpt ++ LaterOptimizations.Nmos ++
+    UndocumentedOptimizations.All ++
+    OptimizationPresets.AssOpt ++ LaterOptimizations.Nmos ++
+    UndocumentedOptimizations.All ++
     OptimizationPresets.Good) {
 
   override def emitIllegals = true