From d23f6e4248ce39d119a63c0ca471bf073bf35127 Mon Sep 17 00:00:00 2001
From: Karol Stasiak <karol.m.stasiak@gmail.com>
Date: Wed, 29 May 2019 14:09:21 +0200
Subject: [PATCH] 6502: improve optimizations using undocumented instructions

---
 .../assembly/mos/opt/UndocumentedOptimizations.scala |  5 +++++
 src/test/scala/millfork/test/IllegalSuite.scala      | 12 ++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/main/scala/millfork/assembly/mos/opt/UndocumentedOptimizations.scala b/src/main/scala/millfork/assembly/mos/opt/UndocumentedOptimizations.scala
index f52a5f4c..291a2576 100644
--- a/src/main/scala/millfork/assembly/mos/opt/UndocumentedOptimizations.scala
+++ b/src/main/scala/millfork/assembly/mos/opt/UndocumentedOptimizations.scala
@@ -89,6 +89,11 @@ object UndocumentedOptimizations {
       val fragment2 = sax :: ctx.get[List[AssemblyLine]](12)
       List(fragment0, fragment1, fragment2).flatten
     },
+    (Elidable & HasOpcode(TXA)) ~
+      (Elidable & HasOpcode(AND)) ~
+      (Elidable & HasOpcode(STA) & HasAddrModeIn(SaxModes) & DoesntMatterWhatItDoesWith(State.A, State.Z, State.N)) ~~> { code =>
+      code(1).copy(opcode = LDA) :: code(2).copy(opcode = SAX) :: code.drop(3)
+    },
   )
 
   def andConstant(const: Constant, mask: Int): Option[Long] = const match {
diff --git a/src/test/scala/millfork/test/IllegalSuite.scala b/src/test/scala/millfork/test/IllegalSuite.scala
index b84a267e..d39ea709 100644
--- a/src/test/scala/millfork/test/IllegalSuite.scala
+++ b/src/test/scala/millfork/test/IllegalSuite.scala
@@ -140,6 +140,10 @@ class IllegalSuite extends FunSuite with Matchers {
         |   byte c
         |   b = five(a)
         |   c = five(a)
+        |   asm {
+        |     iny
+        |     inx
+        |   }
         |   a = c
         |   five(a)
         |   c = a & b
@@ -156,9 +160,9 @@ class IllegalSuite extends FunSuite with Matchers {
     val m = EmuUndocumentedRun("""
         | word output @$c000
         | void main () {
-        |   output = five(5)
+        |   output = five(0, 5)
         | }
-        | word five (byte a) {
+        | word five (byte dummy, byte a) {
         |   return a:a
         | }
       """.stripMargin)
@@ -169,9 +173,9 @@ class IllegalSuite extends FunSuite with Matchers {
     val m = EmuUndocumentedRun("""
         | byte output @$c000
         | void main () {
-        |   output = five(1)
+        |   output = five(0, 1)
         | }
-        | byte five (byte a) {
+        | byte five (byte dummy, byte a) {
         |   byte b
         |   b = a
         |   a += 4