[PicForth] Optimiser problem

[David McNab]

Hi,

I'm trying to write PicForth code which generates subwf instructions, 
and not having much luck.

Sample code:

    variable v1
    : fred
        1 v1 -!
    ;

With optimisation on, this (correctly) generates:

    decf v1,f
    return

I then tried:

    variable v1
    : fred
    disallow-optimizations
        1 v1 -!
    allow-optimizations
    ;

I hoped this would generate something like:

    movlw 1
    subwf v1,f

However, it generates the same as above.

My situation is that I need to decrement 16-bit and 24-bit values to 
zero, which requires generation of code that impacts the Carry bit. But 
I can't work out how to do this in pure PicForth

So what I'm having to do is:

    variable vL
    variable vM
    variable vH

    : v--   ( -- )   \ decrememnts 24-bit value vH:vM:vL

        \ decrement vL
        ]asm
          1  movlw
          vL adjust-bank ,f subwf
        asm[
        c bit-clr? if
          \ got a borrow, decrement vM
          ]asm
            vM ,f subwf \ W still = 1
          asm[
          c bit-clr? if
            \ got a borrow, decrement vH
            1 vH -! \ don't need C, no need for asm code
          then
        then
        restore-bank
    ;

Any thoughts/ideas on all this?

-- 
Cheers
David