Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!elroy!devvax!lwall
From: lwall@devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.sources.d
Subject: Re: Suggested new feature for perl
Message-ID: <1490@devvax.JPL.NASA.GOV>
Date: 5 Mar 88 00:31:52 GMT
References: <7440@ncoast.UUCP>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Lines: 82

In article <7440@ncoast.UUCP> allbery@ncoast.UUCP (Brandon S. Allbery) writes:
: Now that I have perl running on ncoast (!@#$%&* compiler bugs!  It may get
: tossed in favor of gcc as soon as *that* leaves beta testing!)  I have only
: one complaint:  compiling a perl script usually takes longer than running it.

I never noticed a problem with that.  Of course, I'm using a Vax 8600.  :-)

: I would like to suggest, therefore, that a "compile mode" be added to perl
: which saves the compiled program to a file, and that such saved files be loaded
: directly for speed.

Depends on what you mean by "directly".

: I haven't looked at it, so I hope it isn't like awk's
: vaunted compile mode (write everything from &end to sbrk(0) to a file) that
: this would have to be done.

Well, there's various ways you can do this, all with their various tradeoffs.

     1) Do an abort() after compilation and then run a utility which turns
	a core dump into an executable.  Advantages: very fast, and you always
	know you have all the functions you need, and in the version the script
	was written for.  Disadvantage: you carry a lot of excess baggage with
	each compiled perl script--120 K on a Vax, 200 K on a Sun.

     2) Do the awk trick.  Advantages: still very fast, and you don't carry a
        complete copy of perl around with every compiled script.  Disadvantages:
	you have to "recompile" every script if the interpreter changes
	significantly.  It's a kludge that probably won't work everywhere.

     3) Write a code generator that spits out a C program which you link with
	a perl library.  Advantages: same as 1.  Disadvantages: much slower
	compile than 1, and you could end up linking in almost all of perl into
	your script, which gives you the disadvantage of 1 also.  It would
	depend of course on the complexity of the script, but for example a
	script that called "eval" would have to link in the whole bloomin'
	parser.

     4) Do a modified awk trick, in that any pointers are relativized upon
	"compiling", and derelativized upon execution.  Advantage: you could
	probably get away with more modification to perl without needing to
	"recompile" your scripts.

     5) Another modified awk trick: keep, as part of the compiled script,
	a copy of the original perl script, or a reference to it, and
	recompile automatically if the perl version changes (or if the perl
	script changes).  Advantage: you don't need to worry about recompiling.
	Disadvantage: some invokations of your script take much longer than
	others.

     6) Write a routine that dumps out the syntax tree like the dump routines
	currently do if you say perl -D1024, and then write some routines to
	read the syntax tree back in.  You'd also probably have to dump the
	symbol table.  Advantages: probably faster than compiling a perl script
	(though if the size of the info increases much over the size of the perl
	script you can find your performance dominated by I/O costs).  Also
	would probably be compatible with new versions of perl.  Disadvantages:
	Not nearly as fast as whomping in a memory dump, since you have to
	do all the mallocs again.

     7) Compile to some other internal form than a syntax tree which can be
	allocated in one hunk--maybe something like threaded code.  Advantages:
	might execute faster than current perl.  Could probably be made version
	independent, at the cost of a little relocation overhead on startup.
	Disadvantage: I don't have time to rewrite the run-time system.

No doubt there are other ways.  What do you other folks think?

: Larry -- how much of a problem would this be?  (And did you get my bugfix?
: You forgot to trap divide-by-zero, which is rather hard to debug in floating
: point on ncoast.)

Yes, that was fixed in a recent patch.

Well, gotta run.  I'm not going to have a whole lot of time this next month,
so don't expect the patches to come out as fast.  I don't even have time to ack
messages properly, alas.  I try, but if the first shot bounces, I give up.
If you find a bad bug and it isn't fixed within a month, then I probably didn't
get your original message.  On the other hand, if it IS a bad bug, somebody else
has already told me, so no problem, eh?  :-)

Larry Wall
lwall@jpl-devvax.jpl.nasa.gov