Re: [Sbcl-help] bug in (disassemble) ?

[Guenther T. <gue...@gm...>]

On Tue, 2008-12-09 at 20:39 +0000, Christophe Rhodes wrote:

> Guenther Thomsen <gue...@gm...> writes:
> 
> > Am I wrong to expect an "ADD" in the disassembled code below?
> > --8<-- 
> > CL-USER> (defun h (x)
> > 	   (declare (type fixnum x) (optimize (safety 0)))
> > 	    (the fixnum (+ x 3)))
> >
> > STYLE-WARNING: redefining H in DEFUN
> > H
> > CL-USER> (disassemble 'h)
> > ; 02C3D4D2:       488D5118         LEA RDX, [RCX+24]          ; no-arg-parsing entry point
> 
> Yes.  On x86oids, fixnum adds of constants can be implemented using
> the Load Effective Address instruction.  (I haven't measured recently
> to find whether or not this is faster than using ADD, but it has been
> at least at some points in the past.
> 
> Best,
> 
> Christophe


Ah, I see. With a variant of that function (adding 5 instead of 3, the
LEA instruction becomes "LEA RDX, [RCX+40]", the 3 bit left shift is due
to implied type information, I suppose).

Thanks
    Guenther