until-loop condition now also simplified to avoid stack-eval

compiler/src/prog8/compiler/BeforeAsmGenerationAstChanger.kt

@@ -235,6 +235,10 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
     )
 
     private fun simplifyConditionalExpression(expr: BinaryExpression): CondExprSimplificationResult {
+
+        // TODO: somehow figure out if the expr will result in stack-evaluation STILL after being split off,
+        //       in that case: do *not* split it off but just keep it as it is (otherwise code size increases)
+
         var leftAssignment: Assignment? = null
         var leftOperandReplacement: Expression? = null
         var rightAssignment: Assignment? = null
@@ -302,9 +306,21 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
             (binExpr.right as? NumericLiteralValue)?.number!=0)
             throw FatalAstException("0==X should have been swapped to if X==0")
 
-        // TODO simplify conditional expression like in if-statement
+        // simplify the conditional expression, introduce simple assignments if required.
+        // NOTE: sometimes this increases code size because additional stores/loads are generated for the
+        //       intermediate variables. We assume these are optimized away from the resulting assembly code later.
+        val simplify = simplifyConditionalExpression(binExpr)
+        val modifications = mutableListOf<IAstModification>()
+        if(simplify.rightVarAssignment!=null) {
+            modifications += IAstModification.ReplaceNode(binExpr.right, simplify.rightOperandReplacement!!, binExpr)
+            modifications += IAstModification.InsertLast(simplify.rightVarAssignment, untilLoop.body)
+        }
+        if(simplify.leftVarAssignment!=null) {
+            modifications += IAstModification.ReplaceNode(binExpr.left, simplify.leftOperandReplacement!!, binExpr)
+            modifications += IAstModification.InsertLast(simplify.leftVarAssignment, untilLoop.body)
+        }
 
-        return noModifications
+        return modifications
     }
 
     @Suppress("DuplicatedCode")
@@ -327,8 +343,13 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
             (binExpr.right as? NumericLiteralValue)?.number!=0)
             throw FatalAstException("0==X should have been swapped to if X==0")
 
-        // TODO simplify conditional expression like in if-statement
-
+        // TODO simplify the conditional expression, introduce simple assignments if required.
+        // NOTE: sometimes this increases code size because additional stores/loads are generated for the
+        //       intermediate variables. We assume these are optimized away from the resulting assembly code later.
+        // NOTE: this is nasty for a while-statement as the condition occurs at the top of the loop
+        //       so the expression needs to be evaluated also before the loop is entered...
+        //       but I don't want to duplicate the expression.
+        // val simplify = simplifyConditionalExpression(binExpr)
         return noModifications
     }
 

docs/source/todo.rst

@@ -3,7 +3,7 @@ TODO
 
 For next compiler release (7.3)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-- add expression simplification to while and until loops as well.
+...
 
 
 Blocked by an official Commander-x16 v39 release
@@ -14,6 +14,11 @@ Blocked by an official Commander-x16 v39 release
 
 Future
 ^^^^^^
+- simplifyConditionalExpression() should not split expression if it still results in stack-based evaluation
+- remove special code generation for while and util expression
+  by rewriting while and until expressions into if+jump (consider them syntactic sugar)
+  but the result should not produce larger code ofcourse!
+- while-expression should now also get the simplifyConditionalExpression() treatment
 - fix the asm-labels problem (github issue #62)
 - find a way to optimize asm-subroutine param passing where it now sometimes uses the evalstack?
 - document the various compiler command line options in more detail. See "Compiling program code" in the docs

examples/test.p8

@@ -1,16 +1,33 @@
+%import textio
 
 main {
 
     sub start() {
-        byte xx=1
+        ubyte xx=10
 
-        if xx+2 {
-            xx++
+        txt.print("if\n")
+        if xx-2 {
+            txt.print("in if\n")
         }
 
-        sub test() -> ubyte {
+        txt.print("\nwhile\n")
+        xx=6
+        while xx-2 {
+            xx--
+            txt.print_ub(xx)
+            txt.spc()
+        }
+
+        txt.print("\nuntil\n")
+        xx=2
+        do {
             xx++
-            return xx
+            txt.print_ub(xx)
+            txt.spc()
+        } until xx+2==10
+        txt.print("\ndone")
+
+        repeat {
         }
     }