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From: ken@rochester.UUCP (and Vicki Herrieschopper)
Newsgroups: net.lang.mod2
Subject: Re: Modula-2 under BSD 4.2 (long)
Message-ID: <12515@rochester.UUCP>
Date: Mon, 21-Oct-85 11:12:43 EDT
Article-I.D.: rocheste.12515
Posted: Mon Oct 21 11:12:43 1985
Date-Received: Wed, 23-Oct-85 04:48:46 EDT
References: <606@lasspvax.UUCP>
Reply-To: ken@rochester.UUCP (and Vicki Herrieschopper)
Organization: Home for the terminally enabled
Lines: 55
Keywords: it (may still) exist

We too have had some experience with Powell's compiler. If I appear to
be critical, it is because I am leaving out the praises. With a some
(more than a little, certainly) work it could be a production quality
compiler.

In article <606@lasspvax.UUCP> andy@lasspvax.UUCP (Andy Pfiffer) writes:
>The first phase of the compiler parses an individual Modula-2 module and
>compiles it into P-code.  It consists of about 17,000 lines of Pascal
>program and 1,000 lines of YACC grammar.  It includes an optimizer that
>eliminates common subexpressions, moves invariants out of loops, allocates
>registers, and performs other optimizations.
>
>	[this is good clean code...]

Nested modules are not done correctly. It bombs out on some programs.
Also the error messages are not the most informative, i.e. syntax error
at line ..., a la C.

>The second phase of the compiler translates P-code into VAX instructions.
>It consists of about 6,000 lines of Pascal program.  It folds constants
>and selects instructions in order to reduce execution time.
>
>	[this part was a real memory hog and generated bad code for...]
>	[...some constant expressions.]

Complicated expressions can cause this to barf.

>A program to help convert Pascal programs into Modula-2 is provided.
>It consists of about 1,800 lines of Pascal and 1,000 lines of YACC grammar.
>
>	[this works okay...but...]

The Pascal grammar provided is wrong and it objects to some legal
Pascal programs in particular case statements. It is only an hours work
to fix it though. I am trying to send my changes back to Powell (are
you there?).

>SELECTED FEATURES OF THE COMPILER
>Compiles comparable programs faster than the Berkeley Pascal compiler.
>Benchmarks indicate code is comparable to the fastest VAX compilers.
>
>	[True.  The final code was the fastest stuff on the machine!]

The procedure call mechanism is very efficient for "internal" procedures.
This compiler was mentioned as an example of software RISCiness in a
recent CACM article on RISC architectures.

A good deal if you can still get it. I hear Digital is considering
using Modula-2 as their systems language. However the ETH compiler
may give it a run for the money, see a previous announcement.

	Ken
-- 
UUCP: ..!{allegra,decvax,seismo}!rochester!ken ARPA: ken@rochester.arpa
USnail:	Dept. of Comp. Sci., U. of Rochester, NY 14627. Voice: Ken!