overview

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\"#@(#)overview	4.1	Ultrix	7/17/90
.po 1i
.nr PO 1i
.DA "February 29, 1984"
.SH
OVERVIEW OF COMPILER
.LP
The DECWRL Modula-2 compiler distribution consists of several programs.
The compiler itself is divided into three phases:
the front end, the back end, and the intermodule checker.
There is also a program to invoke the various phases of the compiler,
a small runtime library,
some updates to DBX, and a tool for helping convert programs from Pascal to
Modula-2.
.LP
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.
.LP
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.
.LP
The intermodule checker examines a collection of object modules to be sure they
are consistent.
It consists of about 2,500 lines of Modula-2 program.
Optionally, it will recompile any out-of-date modules.
.LP
The mod command examines its argument list and invokes the various phases of
the compiler to compile programs.
It consists of about 400 lines of C program.
.LP
There is a small runtime library provided to perform I/O, allocate and
release memory, do some standard string functions, and interface to the Unix
libraries and system calls.
It consists of about 800 lines of C and Modula-2 program.
.LP
The DBX debugger is used to debug Modula-2 programs.
A set of updates to the 4.2 version of DBX is provided
(Since DBX is part of the 4.2BSD distribution, we cannot distribute the whole
debugger).
.LP
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.
.LP
The benchmark program used to compare different compilers is also
supplied.
.SH
SELECTED FEATURES OF THE COMPILER
.LP
Compiles comparable programs faster than the Berkeley Pascal compiler.
Benchmarks indicate code is comparable to the fastest VAX compilers.
.LP
Built-in I/O library similar to Unix printf/scanf.
.LP
Automatic recompilation based on actual dependencies, not timestamps, in order
to minimize recompilations.
.LP
Generated code is compatible with Berkeley Pascal and Unix C.
Easy to call Pascal or C from Modula-2 and vice-versa.
.LP
Accepts the language as defined in the Modula-2 report.
Uses compile-time switches to relax restrictions in the case of reserved
words and identifiers.
.SH
COMPILER ANNOUNCEMENT 1/31/84
.LP
The Western Research Laboratory of Digital Equipment Corporation is pleased
to announce the availability of a new, experimental Modula-2 compiler for
the VAX and UNIX for university use.  We are licensing interested colleges
and universities to receive and use this compiler for internal, noncommercial
use for a fee of $100 to cover our distribution costs.
.LP
The compiler was designed and built by Michael L. Powell and it appears to
be one of the best compilers for the VAX in terms of the efficiency of the
generated code.  The error messages are slightly better than those from the
Unix C compiler and the compile time is slightly worse.  Below is a table
of execution times on a set of ten benchmarks that John Hennessy at Stanford
has assembled.  All the times are in CPU seconds on a VAX 11/780 with FPA.
All compilers were asked to generate the best code they could and all
optional run time checks were turned off.  All versions of the programs
were as syntactically and semantically similar as possible.
.DS L
Prog. Cambridge BerkeleyUnix  DEC     DEC   DEC  VAXElan Stanford DEC
 Name  Modula-2 Pascal   C    Pascal   C  Bliss32 Pascal Pascal Modula-2
========================================================================
 Perm     4.9    2.7    2.6    2.5    2.5    2.5    2.5    2.2    2.0
 Towers   6.1    2.8    2.6    2.6    2.7    2.5    2.6    2.1    1.9
 Queens   2.8    1.6    1.0    1.1    0.7    0.7    0.9    1.5    0.9
 Intmm    4.9    2.2    1.7    1.1    0.8    1.4    0.8    0.7    0.8
 Mm       5.0    2.7    2.2    1.1    1.3    1.4    0.8    0.7    0.9
 Puzzle  24.6   12.9   12.4    6.2    4.9    5.8    6.5    4.9    4.1
 Quick    2.8    1.7    1.2    1.2    0.8    0.8    0.8    1.0    0.8
 Bubble   5.5    3.0    1.7    1.3    1.0    1.1    0.9    1.4    1.0
 Tree     6.7    6.4    6.2    4.1    3.4    3.2    3.8    1.9    1.9
 FFT      9.7    4.8    4.1    2.5    2.6    1.5    1.2    1.8    1.6
Int Comp  9.9    5.5    4.8    3.5    3.1    3.1    3.1    2.6    2.3
Real Com 14.2    7.7    6.7    4.6    4.3    3.9    3.7    3.4    3.1
.DE
.LP
Doing benchmarks is always tricky and is especially difficult on a VAX 11/780
because of the peculiar interactions between the instruction prefetch buffer
and instruction alignment on word boundaries.  Variations on the order of 10%
because of changes in alignment are not unusual.  The integer and real
composite numbers in the last two lines are Hennessy's weighted averages
of the previous lines -- his attempt to summarize the results.  The above
performance information is provided for guidance only.  Your mileage may vary.
.LP
If you are a college or university and are interested in this compiler,
we can send you some tech reports and copies of the license agreement
that you should have signed by the appropriate licensing office of your
institution.  We can then send you a tar tape that you should be able to
install and run with no more than the usual amount of associated grief
on Berkeley Unix 4.x BSD.  There is no Unix material on the distribution
so we don't need to see your Unix license.  The distribution also includes
a program that does most of the translation of Pascal programs into Modula-2.
.DS
	{...decvax|...ucbvax}!decwrl!powell
or
	[e-mail]
or
	Michael L. Powell
	Digital Equipment Corporation
	Western Research Laboratory
	4410 El Camino Real
	Los Altos, CA  94022
.DE
.LP
This compiler has a number of internal users and we feel it is quite
reliable.  However, new users often find new bugs so we expect to hear
from some of those who try it and we expect to be distributing bug
fixes in a moderately prompt fashion for a while.  We may also have
some additional extensions to distribute as we gain more experience
with the language and hear from other users.
.LP
Please be fully aware that this experimental compiler is not a DEC product
and is not for sale.  Our aim in distributing this compiler is a public
service one.  The license agreement does, however, protect DEC's option
to make this compiler into a product someday.