Re: [cc65] optimizer?

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From: Ullrich von Bassewitz (
Date: 2001-06-24 22:04:55


On Sun, Jun 24, 2001 at 09:32:30PM +0200, groepaz wrote:
> well, ofcoz optimization should be somehow control-able on sourcecode
> level..... so the programmer can exclude certain routines of which he
> knows they are already optimal.... other than that, all those
> optimization would never break the code (result in non-working code)
> but instead _maybe_ make it perform worse than before.... that can
> easily be determined through profiling (aka testing ;D) though, so i
> guess one can live with that.

What about something like

        acia    = $DC00
	data    = $00

     	lda     acia+data		; dummy read
	lda  	#$00

The first load is a dummy read, but it is needed in some way to initialize
hardware, acknowledge an interrupt or whatever. An optimizer would have a
really hard time to figure this out.

> uhm well... would there be a real difference in optimizing binary vs
> assembler code ? (except with assembler code you get much more
> information about the code structure, dont have to guess code adresses
> that are loaded as 8bit lo/hi pairs etc)

You don't have to mess with expressions when using binary code. It is easy to
detect that things like

        foo     = $02
        bar  	= $02
    	lda	foo
    	lda	bar

are accessing the same location. Or what about

        foo     = $02
        bar  	= $01
    	lda	foo
    	lda	bar*2

Having an optimizer working on source code, you need to mimic the complete
symbol handling of the assembler, including local symbols and so on. Or
something like

       	.import	foo, bar

	jmp	foo
	jmp	bar

foo and bar may in fact resolve to the same address which would allow some
speed and/or size optimizations, but an optimizer working on source code would
not have the necessary knowledge, while this would be easy to detect when
working with binary code.



Ullrich von Bassewitz                        
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