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From: johnl@ima.UUCP
Newsgroups: mod.compilers
Subject: Re: Debuggers
Message-ID: <518@ima.UUCP>
Date: Thu, 12-Mar-87 03:31:33 EST
Article-I.D.: ima.518
Posted: Thu Mar 12 03:31:33 1987
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About 7 years ago I did some very preliminary studies involving the
BLISS-32 code generator while I was at Digital. I managed to convince
myself that it was possible to derive source code from the optimized
object code, however, one would have to make extensive use of
heuristics.

Unfortunately, I was unable to convince management that there was
sufficient payback to warrant a project. (I used the concept of filtering
optimized object code through a source generator, and then filtering
that back through the optimizer. They weren't interested: the existing
optimizations were good enough, and I was proposing orders of
magnitude more time to do a compile.)

The heuristics would only be good for a certain class of compilers
and their code generators. The peephole optimizers and cross jumping
done by different compilers would create an enormous explosion of 
possible source codes.

I eventually came to the conclusion that there are two possible uses
of 'compiling object into source'. 1) As a study in a given compiler's
effectiveness at handling particular classes of programs. and 2)
as an analysis tool to see how a computer would execute a program.
The original thought of increasing code optimization would turn out
to be an impractical use; with a good optimizer in the first place,
you would not obtain practical results after the second iteration.

If you're interested, I'll try to dig up my notes.

--Bruce Dawson
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