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From: dwp@willett.pgh.pa.us (Doug Philips)
Newsgroups: comp.lang.forth
Subject: Re: Forth optimization  (was Re: Postfixer Forth)
Message-ID: <1676.UUL1.3#5129@willett.pgh.pa.us>
Date: 6 Sep 90 03:33:15 GMT
References: <1990Aug29.171704.15174@idacom.uucp>
Organization: String, Scotch tape, and Paperclips.  (in Pgh, PA)
Lines: 35

In <1990Aug29.171704.15174@idacom.uucp>, andrew@idacom.uucp (Andrew Scott) writes:
>             I would have to save all the compilation tokens in the entire IF
> construct before the decision could be made.  Currently, the optimizer is
> quite small because I only have to queue up 4 tokens at most (the longest
> sequence in the optimization rules set is 4 words).

And you could always do the code motion by hand, or recode assembler if
it were really critical.

> There are many more optimizations that my compiler could tackle, but I don't
> want to end up with a mammoth system.  I get decent results from the sequence
> optimizations I perform now.

The first 90% takes 90%, the last 10% takes the other 90%

> I was going to experiment with an optimizer that worked at the assembly
> language level.  Each Forth primitive (like DUP) could be coded in "machine"
> primitives (like POP and PUSH).  Redundant POPs and PUSHes could be eliminated
> and values could remain in registers over a long span of code.  Movement
> to the stack in memory would only take place when necessary.  This approach
> might yield big speed improvements on non-Forth processors.

Do you mean that you'll have another virtual machine with PUSH POP etc.
or do you mean the real machine level instructions.  I think you could
probably do a good machine code peephole optimizer that way.  Of course,
if you do automatic inlining (instead of having a special word :: ) you
would want to delay "optimization" until the end.  Maybe with a multiple
cfa scheme you could have both the optimized and unoptimized code,
depending on what you need to use at the time.

-Doug

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