[COFF] [TUHS] Re: machine code translation, as mental architecture models

[Dan Cross]

On Wed, Jul 10, 2024 at 9:54 PM John R Levine <johnl at taugh.com> wrote:
> On Wed, 10 Jul 2024, Dan Cross wrote:
> > It's not clear to me why you suggest with such evident authority that
> > Knuth was referring only to serialized instruction emulation and not
> > something like JIT'ed code; true, he doesn't specify one way or the
> > other, but I find it specious to conclude that that implies the
> > technique wasn't already in use, or at least known.
>
> The code on pages 205 to 211 shows an instruction by instruction
> interpreter.  I assume Knuth knew about JIT compiling since Lisp systems
> had been doing it since the 1960s, but that's not what this section of the
> book is about.

Sure.  But we're trying to date the topic here; my point is that
JITing was well known, and simulation was similarly well known; we
know when work on those books started; it doesn't seem that odd to me
that combining the two would be known around that time as well.

> One of the later volumes of TAOCP was supposed to be about
> compiling, but it seems unlikely he'll have time to write it.

Yes; volumes 5, 6 and 7 are to cover parsing, languages, and compilers
(more or less respectively).  Sadly, I suspect you are right that it's
unlikely he will have time to write them.

> >> We've been discussing batch or JIT translation of code which gives
> >> much better performance without a lot of hardware help.
> >
> > JIT'd performance of binary transliteration is certainly going to be
> > _better_ than strict emulation, but it is unlikely to be _as good_ as
> > native code.
>
> Well, sure, except in odd cases like the Vax compiler and reoptimizer
> someone mentioned a few messages back.

I think the point about the VAX compiler is that it's an actual
compiler and that the VAX MACRO-32 _language_ is treated as a "high
level" programming language, rather than as a macro assembly language.
That's not doing binary->binary translation, that's doing
source->binary compilation.  It's just that, in this case, the source
language happens to look like assembler for an obsolete computer.

        - Dan C.