Hi Olin,

I liked your constructive criticism.But there are two solution for
the problem you pointed out.

Solution 1:

As soon as the whole Hex File has been loaded and Disassembled,
the Optimizer could search for a pattern like

BSF EECON1,EEPGD
;...(Any or No instructions that Don't modify EECON1)...
BSF EECON1,RD

If this sequence is detected, The optimizer might set a flag.
later on while optimizing, it could ignore instructions which
seem absurd to it.

Solution 2:

There is one more way of detecting it.
Its prudent programming practice to have a goto to skip a table
or any "data" in instructions.

it could be like:

goto skip_table
table:
addwf PCL
dt "0123456789"
skip:
;..(Any instructions)...


Or you might place the table at the end of the program.

If anyone does not do this, most probably his program won't work
as he wants it to(Unless he is someone like Dimitry).

The optimizer could identify these skips and Ignoe the code between them.

But, removing tables which are never called *MUST* be done.

The end user will always have full control over what Optimizations should
be done and what should not be done.

And for a novice user, all optimizations will be realtively safe.
You can always disable the optimizations which you don't like.

Jeethu Rao


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Tuesday, July 03, 2001 5:01 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Compiler


> I'm thinking of writing an Optimizer for PIC Hex Files.
> It would take in a hex file, Disassemble it, and then
> try various optimizations.

This is impossible in the general sense.  For example, suppose you
encountered

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

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