"not x" as a condition (if, while, until) is optimized into "x==0", this avoids calculating the value

compiler/src/prog8/compiler/BeforeAsmGenerationAstChanger.kt

@@ -185,7 +185,15 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
         return noModifications
     }
 
+    @Suppress("DuplicatedCode")
     override fun after(ifStatement: IfStatement, parent: Node): Iterable<IAstModification> {
+        val prefixExpr = ifStatement.condition as? PrefixExpression
+        if(prefixExpr!=null && prefixExpr.operator=="not") {
+            // if not x -> if x==0
+            val booleanExpr = BinaryExpression(prefixExpr.expression, "==", NumericLiteralValue.optimalInteger(0, ifStatement.condition.position), ifStatement.condition.position)
+            return listOf(IAstModification.ReplaceNode(ifStatement.condition, booleanExpr, ifStatement))
+        }
+
         val binExpr = ifStatement.condition as? BinaryExpression
         if(binExpr==null || binExpr.operator !in comparisonOperators) {
             // if x  ->  if x!=0,    if x+5  ->  if x+5 != 0
@@ -201,7 +209,15 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
         return noModifications
     }
 
+    @Suppress("DuplicatedCode")
     override fun after(untilLoop: UntilLoop, parent: Node): Iterable<IAstModification> {
+        val prefixExpr = untilLoop.condition as? PrefixExpression
+        if(prefixExpr!=null && prefixExpr.operator=="not") {
+            // until not x -> until x==0
+            val booleanExpr = BinaryExpression(prefixExpr.expression, "==", NumericLiteralValue.optimalInteger(0, untilLoop.condition.position), untilLoop.condition.position)
+            return listOf(IAstModification.ReplaceNode(untilLoop.condition, booleanExpr, untilLoop))
+        }
+
         val binExpr = untilLoop.condition as? BinaryExpression
         if(binExpr==null || binExpr.operator !in comparisonOperators) {
             // until x  ->  until x!=0,    until x+5  ->  until x+5 != 0
@@ -211,7 +227,15 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, private val o
         return noModifications
     }
 
+    @Suppress("DuplicatedCode")
     override fun after(whileLoop: WhileLoop, parent: Node): Iterable<IAstModification> {
+        val prefixExpr = whileLoop.condition as? PrefixExpression
+        if(prefixExpr!=null && prefixExpr.operator=="not") {
+            // while not x -> while x==0
+            val booleanExpr = BinaryExpression(prefixExpr.expression, "==", NumericLiteralValue.optimalInteger(0, whileLoop.condition.position), whileLoop.condition.position)
+            return listOf(IAstModification.ReplaceNode(whileLoop.condition, booleanExpr, whileLoop))
+        }
+
         val binExpr = whileLoop.condition as? BinaryExpression
         if(binExpr==null || binExpr.operator !in comparisonOperators) {
             // while x  ->  while x!=0,    while x+5  ->  while x+5 != 0

compiler/src/prog8/compiler/Compiler.kt

@@ -324,7 +324,8 @@ private fun writeAssembly(program: Program,
     program.processAstBeforeAsmGeneration(compilerOptions, errors)
     errors.report()
 
-    // printAst(program)
+//    println("*********** AST RIGHT BEFORE ASM GENERATION *************")
+//    printAst(program)
 
     compilerOptions.compTarget.machine.initializeZeropage(compilerOptions)
     val assembly = asmGeneratorFor(compilerOptions.compTarget,

docs/source/todo.rst

@@ -3,7 +3,7 @@ TODO
 
 For next compiler release (7.2)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-- optimize "if not x" / "while not x" to not actually calculate the whole "not x" value first --> transform in to "x==0" in these conditional statements?
+...
 
 
 Blocked by Commander-x16 v39 release

examples/test.p8

@@ -1,30 +1,47 @@
 %import textio
-%import floats
+; %import floats
 %zeropage basicsafe
 
 main {
   sub start() {
-    uword xx= $2000
-    ubyte yy=$30
-    ubyte zz=9
-    sys.memset(xx+200, yy*2, ~yy)
+    word xx=0
 
-    if yy & %10000 {
-        yy++
+    if not xx {
+        txt.print("xx is zero\n")
     }
 
-    @($c030) = 10
-    @(~xx) *= 2
-    txt.print_ub(@($c030))
+    while not xx {
+        xx ++
+    }
 
-    float f1 = 1111.11
-    float f2 = 2222.22
-    float[] fa = [2222.22, 3333.33]
+    do {
+        xx--
+    } until not xx
 
-    swap(f1, fa[1])
-    floats.print_f(f1)
-    txt.nl()
-    floats.print_f(fa[1])
+    if not xx {
+        txt.print("xx is zero\n")
+    }
+
+;    ubyte yy=$30
+;    ubyte zz=9
+;    sys.memset(xx+200, yy*2, ~yy)
+;
+;    if yy & %10000 {
+;        yy++
+;    }
+;
+;    @($c030) = 10
+;    @(~xx) *= 2
+;    txt.print_ub(@($c030))
+;
+;    float f1 = 1111.11
+;    float f2 = 2222.22
+;    float[] fa = [2222.22, 3333.33]
+;
+;    swap(f1, fa[1])
+;    floats.print_f(f1)
+;    txt.nl()
+;    floats.print_f(fa[1])
 
   }
 }