use less tempvars

codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt

@@ -2172,23 +2172,21 @@ internal class AugmentableAssignmentAsmGen(private val program: PtProgram,
                 // the other variable is a BYTE type so optimize for that
                 when (operator) {
                     "+" -> {
+                        // name += byteexpression
                         if(valueDt==DataType.UBYTE) {
-                            // TODO optimize: don't use scratch var
-                            asmgen.assignExpressionToVariable(value, "P8ZP_SCRATCH_B1", valueDt)
+                            asmgen.assignExpressionToRegister(value, RegisterOrPair.A, false)
                             asmgen.out("""
-                                lda  $name
                                 clc
-                                adc  P8ZP_SCRATCH_B1
+                                adc  $name
                                 sta  $name
                                 bcc  +
                                 inc  $name+1
 +""")
                         } else {
-                            // TODO optimize: don't use scratch var
-                            asmgen.assignExpressionToVariable(value, "P8ZP_SCRATCH_B1", valueDt)
+                            asmgen.assignExpressionToRegister(value, RegisterOrPair.A, true)
                             asmgen.out("""
                                 ldy  #0
-                                lda  P8ZP_SCRATCH_B1
+                                cmp  #0
                                 bpl  +
                                 dey         ; sign extend
 +                               clc
@@ -2200,7 +2198,7 @@ internal class AugmentableAssignmentAsmGen(private val program: PtProgram,
                         }
                     }
                     "-" -> {
-                        // TODO optimize: don't use scratch var
+                        // name -= byteexpression
                         asmgen.assignExpressionToVariable(value, "P8ZP_SCRATCH_B1", valueDt)
                         if(valueDt==DataType.UBYTE)
                             asmgen.out("""

docs/source/todo.rst

@@ -3,7 +3,6 @@ TODO
 - fix on c64 target: examples/cube3d-float (broken since 9.3 with the evalstack removal)  it works on x16 target, oddly enough.
   More detailed and simpler code for this problem in floatproblem64.p8 / floatproblem64.asm (the minified version)
 
-- optimize: search for TODO optimize: don't use scratch var
 - prefix prog8 subroutines with p8s_ instead of p8_ to not let them clash with variables in the asm?
 - allow 'chained' array indexing for expressions:  value = ptrarray[0][0]
 - allow 'chained' array indexing for assign targets:  ptrarray[0][0] = 42   this is just evaluating the lhs as a uword pointer expression

examples/test.p8

@@ -4,11 +4,10 @@
 main {
     sub start() {
 
-        uword ww= 300
-        @($4000) = 100
-        ww -= @($4000)
-        ww -= 100
-        txt.print_uw(ww)        ; 100
+        byte bb = 20
+        word ww= 300
+        ww += bb*3
+        txt.print_w(ww)        ; 240
 
 ;        ubyte index = 100
 ;        ubyte[] t_index = [1,2,3,4,5]