Re: car/cdr chain optimization

Nice, thanks. Maybe I'll write a Lisp macro to handle the easy cases while
you work on interfacing to LLVM....

A lot of Maxima code today looks like:

(cond ((numberp x) ...)
      ((atom x) ...)
      ((eq (caar x) 'mplus) ...) ;includes 2 listp checks
      ((eq (caar x) 'mtimes ...) ;includes 2 listp checks
       ...)

It should be pretty straightforward to translate that to

(defun unchecked-car (x) (car x))  ;; how do you write these?
(defun unchecked-car (x)
    (declare (optimize (speed 3) (space 3) (safety 0)))
    (cdr x))  ;; does this work?

(cond ((numberp x) ...)
      ((atom x) ...)
      ((eq (setq x-caar (car (unchecked-car x)) 'mplus)) ...) ; atom
already checked
      ((eq x-caar 'mtimes) ...)
       ...)




On Mon, Feb 3, 2025 at 7:03 PM Douglas Katzman <[email protected]> wrote:

> The SBCL compiler is pretty much unaware of the concept of common
> subexpression elimination.  One of my thoughts about how to really improve
> it to compile into LLVM IR.  That idea brings with it a world of issues to
> resolve in order to get there, but gives a glimmer of hope toward availing
> ourselves of modern compiler techniques.
> I wanted to see what would happen if we compile a C program that is nearly
> equivalent to your EQ expression with type-check - does LLVM eliminate the
> redundant read and type-check? Indeed it does. I've attached the source and
> asm.  The asm contains only 3 memory loads (one is disguised as a CMP in
> mem-to-reg form) and 2 conditional branches.  See attached if you're
> curious.
>

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