optimized repeat loop for word counts

compiler/src/prog8/compiler/target/cpu6502/codegen/AsmGen.kt

@@ -1011,14 +1011,8 @@ internal class AsmGen(private val program: Program,
         // note: A/Y must have been loaded with the number of iterations!
         if(constIterations==0)
             return
-        if(constIterations==null) {
-            out("""
-                cmp  #0
-                bne  +
-                cpy  #0
-                beq  $endLabel   ; skip loop if zero iters
-+""")
-        }
+        // no need to explicitly test for 0 iterations as this is done in the count down logic below
+
         val counterVar = makeLabel("repeatcounter")
         out("""
                 sta  $counterVar
@@ -1027,7 +1021,7 @@ $repeatLabel    lda  $counterVar
                 bne  +
                 lda  $counterVar+1
                 beq  $endLabel
-+               lda  $counterVar
+                lda  $counterVar
                 bne  +
                 dec  $counterVar+1
 +               dec  $counterVar

examples/test.p8

@@ -2,6 +2,37 @@
 %zeropage basicsafe
 
 main {
+    sub start() {
+        bench()
+        txt.nl()
+
+        uword total
+        ubyte bb
+        uword ww
+
+        for bb in 0 to 255 {
+            total = 0
+            repeat bb
+                total++
+            txt.print_uw(total)
+            txt.spc()
+            txt.spc()
+        }
+
+        txt.nl()
+        txt.nl()
+
+        for ww in 0 to 600 {
+            total = 0
+            repeat ww
+                total++
+            txt.print_uw(total)
+            txt.spc()
+            txt.spc()
+        }
+
+    }
+
 
     sub iter(uword iterations) -> uword {
         uword total = 0
@@ -26,7 +57,7 @@ main {
         return total
     }
 
-    sub start() {
+    sub bench() {
         uword xx1
         uword xx2
         uword xx3