some more obvious optimizations for X+X and X-X

compiler/res/prog8lib/prog8lib.asm

@@ -1772,7 +1772,6 @@ _loop_hi	ldy  _index_first
 
 ror2_mem_ub	.proc
 		; -- in-place 8-bit ror of byte at memory location on stack
-		; TODO use self modifying code here
 		inx
 		lda  c64.ESTACK_LO,x
 		sta  c64.SCRATCH_ZPWORD1
@@ -1789,7 +1788,6 @@ ror2_mem_ub	.proc
 
 rol2_mem_ub	.proc
 		; -- in-place 8-bit rol of byte at memory location on stack
-		; TODO use self modifying code here
 		inx
 		lda  c64.ESTACK_LO,x
 		sta  c64.SCRATCH_ZPWORD1

compiler/src/prog8/compiler/Main.kt

@@ -165,6 +165,9 @@ private fun optimizeAst(programAst: Program, errors: ErrorReporter) {
         if (optsDone1 + optsDone2 == 0)
             break
     }
+    // because simplified statements and expressions could give rise to more constants that can be folded away:
+    programAst.constantFold(errors)
+    errors.handle()
 }
 
 private fun postprocessAst(programAst: Program, errors: ErrorReporter, compilerOptions: CompilationOptions) {

compiler/src/prog8/optimizer/ExpressionSimplifier.kt

@@ -258,6 +258,14 @@ internal class ExpressionSimplifier(private val program: Program) : AstWalker()
     }
 
     private fun optimizeAdd(expr: BinaryExpression, leftVal: NumericLiteralValue?, rightVal: NumericLiteralValue?): Expression? {
+        if(expr.left.isSameAs(expr.right)) {
+            // optimize X+X into X *2
+            expr.operator = "*"
+            expr.right = NumericLiteralValue.optimalInteger(2, expr.right.position)
+            expr.right.linkParents(expr)
+            return expr
+        }
+
         if (leftVal == null && rightVal == null)
             return null
 
@@ -278,6 +286,11 @@ internal class ExpressionSimplifier(private val program: Program) : AstWalker()
     }
 
     private fun optimizeSub(expr: BinaryExpression, leftVal: NumericLiteralValue?, rightVal: NumericLiteralValue?): Expression? {
+        if(expr.left.isSameAs(expr.right)) {
+            // optimize X-X into 0
+            return NumericLiteralValue.optimalInteger(0, expr.position)
+        }
+
         if (leftVal == null && rightVal == null)
             return null
 

examples/test.p8

@@ -1,33 +1,9 @@
 %import c64lib
 %import c64utils
-%zeropage dontuse
 
 
 main {
     sub start() {
-        ubyte ub
-        byte bb
-        word ww
-        uword uw
-        uword auw
-        word aww
-        byte ab
-        ubyte aub
-
-        ; TODO optimize all of these:
-        ab = bb+bb      ; TODO bb * 2?  (bb<<1)
-        ab = bb+bb+bb
-        aww = ww+ww
-        aww = ww+ww+ww
-
-        aub = ub+ub
-        aub = ub+ub+ub
-        auw = uw+uw
-        auw = uw+uw+uw
-
-
-        A = A+A
-        Y=Y+Y+Y
 
     }
 }