On a related (optimization) theme,

On Fri, Jul 2, 2021 at 12:58 PM Paul Winalski <paul.winalski@gmail.com> wrote:
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-Paul W..

On 7/1/21, scj@yaccman.com <scj@yaccman.com> wrote:
> I saw this post and it reminded me of a meeting that Dennis and I had
> with Bill Wulf.  At one point, Dennis decided to write an optimizer but
> gave up after a week or two because when he had coded the data
> structures he needed he had filled up the PDP-11 memory!   It was a very
> strong part of the Unix meme that Unix and C would run on small
> computers since most of the universities couldn't afford bigger ones at
> the time.
> When PCC came along and started running on 32-bit machines, I started
> thinking about algorithms for optimization.  A problem that I had no
> good solution for could be illustrated by a simple piece of code:
>          x = *p;
>          y = *q;
>          q gets changed
>          *q = z;
> The question is, do I need to reload x now because q might have been
> changed to point to the same place as p?   At around this time, Al Aho
> was invited to go to CMU and give a talk, and he invited me to come with
> him.  We spent about an hour and a half one-on-one with Bill Wulf -- I
> seem to remember a lot of mutual respect going on.  But when I asked him
> about my problem, he really didn't have much to say about it.  I finally
> got him to agree that his compiler had a bug.  But he said there was a
> flag they could set on the compiler that would turn of optimization and
> if your program had mysterious bugs, you should use the flag.
> I recall that Al, always in search of better algorithms, was a bit
> disappointed -- I was a bit more pragmatic about it.  On the whole, it
> was a good meeting, and the "Engineering ... Compiler" book was one of
> my favorites when it came out.
> Steve