> >    MOVLW h'3A'
> >
> > That could be the low or high byte of an address, or just an arbitrary
> > constant.  There are lots of other gotchas too.  You need to know the
> > original intent of the code to do any meaningful optimizations.
>
> Olin's example above is not really clear, so let me elaborate slightly.

Sorry, I'll explain why this is a show-stopping gotcha.  A HEX file contains
raw instructions after address symbols have been resolved and linked.  To do
any meaningful optimizing, you will have to move instructions around.  Since
some instructions will now be at different addresses, you have to adjust the
references to those addresses.  That can be done with GOTO and CALL
instructions, but what about the example above?  Here are a few examples of
the code that could have produced that MOVLW instruction:

   MOVLW   h'3A'     ;get the official number of glorks per snorp
   MOVLW   low table ;get low byte of table start address
   MOVLW   high table ;get high byte of table start address
   MOVLW   low blog+3 ;get address of the count field in the BLOG structure

You're screwed because there is no way to distinguish these cases, so you
have no idea how, if at all, to adjust the 3Ah value.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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