TweetFollow Us on Twitter

Jul 96 Factory Floor
Volume Number:12
Issue Number:7
Column Tag:From The Factory Floor

A Little CodeWarrior History

By Dave Mark

This month, we’re going to talk with John McEnerney, one of the compiler writers
at Metrowerks.

Dave: How did you first hook up with Metrowerks?

John: I first met Greg Galanos when I was the development manager at Symantec’s Language Products Group. Greg was trying to get me interested in doing some sort of deal with the fledgling Metrowerks, and I mostly ignored him because they were trying to compete aggressively with my first product, THINK Pascal. I would have never guessed that a few years later he would offer me the best opportunity of my career.

Dave: When did you leave Symantec?

John: I left Symantec in October ’92, taking about 6 months off to figure out what I wanted to do next. I didn’t have any real plans, but I figured I’d find some way to do PowerPC work. I didn’t relish the thought of trying to write an entire C++ compiler, so I considered doing a Pascal product on my own.

Around this time, Greg had heard from Rich Siegel (of BBEdit fame) that I was no longer at Symantec, and he called me right away. The first thing he said to me was, “describe your dream job,” and I told him I wanted to write a PowerPC code generator for the upcoming Power Macintoshes. I flew to Montreal to meet him and his partner, Jean Belanger. We had some Italian food, drank some wine, and they told me a little about their Pascal and Modula products. I was really hot to write a PowerPC backend, but I was not that impressed with their technology. We talked about various contracts, but I didn’t have a really solid feeling yet.

Dave: What finally convinced you to go with Metrowerks?

John: In February ’93, Greg asked me to meet with him in Palo Alto to get a look at a C compiler that they had just acquired; a guy named Andreas Hommel in Hamburg had been writing it as a hobby. It ran on the Macintosh, had a simple but nice IDE reminiscent of early versions of THINK C, and it was fast. I spent about an hour looking through the source code: it was well organized, the compiler front-end and back-end were cleanly separated, the code was easy to follow, and in addition to being a full ANSI C compiler, it had a lot of the C++ language implemented already.

It was clear that Greg had found a diamond in the rough, the perfect platform for a native PowerMacintosh product. A few hours later we had a contract - I had about 6-8 months to write a PowerPC back-end and linker. Andreas would finish the C++ language implementation, and a few guys in Montreal (Berardino Baratta, Marcel Achim) would work on the IDE and a new Pascal front-end. We immediately hired Greg Dow, who had written the THINK Class Library for Symantec when I was there, to write a new application framework: PowerPlant.

We must have hooked up with Jordan Mattson from Apple around this time, because a week or so later he sent me one of their RS/6000s to help me get started. Between him and Alan Lillich, who I had met at all the early PowerPC meetings that Apple had been holding for their key developers, I got pretty much everything I needed from Apple.

So, I now had a contract to do the most interesting work I could imagine; all I had to do was figure out where to start.

Dave: What was it like working with Andreas’ compiler?

John: Andreas’ compiler was pretty traditional in its organization. The front-end made a single pass over the source code, performing lexical analysis as it went, and generated an intermediate representation (IR) that consisted of expression trees, labels, and branches. It took about a week to totally remove the 68K code generator from the rest of the compiler, and put in stub routines where the front-end and the back-end connected so that everything would still link. If I could fill in all the stub routines in exactly the right way, we’d have a PowerPC compiler.

The first thing I did was write a routine that dumped the IR in human-readable form - I don’t know how Andreas got his 68K code generator to work without that, I guess he can keep more in his head than I can. Looking at the expression trees on the screen allowed me to visualize how the code generator would proceed.

Most CISC compilers spend a lot of time working on the IR trees themselves. Traditional global optimizations like loop-invariant code motion or common subexpression elimination are performed by rewriting the IR trees into optimized IR trees. The code generator gathers information about the shape of the trees, deciding how many registers will be needed, which addressing modes will be used, etc. After instructions are generated they are largely ignored except for small “peephole” optimizations. (A notable exception to this is the gcc compiler, which transforms the expressions into a simple algebraic representation called RTL and uses repeated “peephole” optimizations derived from a machine description to coalesce these RTL expressions into complex instructions and addressing modes.)

Most of the RISC compilers that I’d read about in the compiler literature used a different approach: immediately transform the IR trees into a low-level representation that was similar or identical to the actual RISC instructions of the target machine, and perform all optimizations at the machine instruction level. I decided to use this technique in my PowerPC code generator.

Dave: What was your basic approach to code generation?

John: Strange as it may seem, the first part of the code generator I actually wrote was the instruction scheduler - the phase that reorders instructions to minimize latencies caused by load delays, and to permit floating-point and integer instructions to execute in parallel. I needed to know if my low-level representation - I called it a “pcode” (no relation to the UCSD Pascal pcode) - had enough information for all the phases I would eventually write, and since the scheduler needed a lot of information, it would serve to prove the design of the pcode. Of course, I had to rewrite the scheduler twice more: the first time was to fix the original one, which had some design flaws, and the second time was to make it more general to support 601, 603 and 604 CPUs.

Once I finished the scheduler, I had my data structures organized and all the support routines in place, so I started writing the instruction selection phase - the “guts” of the code generator. This phase visits the IR tree and generates pcode. It does try to recognize certain tree patterns, like opportunities for FMADD and FMSUB routines, but since there are no complex addressing modes and very few complex instructions, it is mostly a straightforward translation to PowerPC instructions.

To get short-term results, I wrote a quick-and-dirty register allocator, and some code to display the generated pcode instructions, and was able to get most of the code generation debugged this way. I decided to use a proprietary object code format, derived from the one we were already using in our 68K compiler and linker, since I could get this working faster than trying to write an XCOFF linker. I spent a few weeks getting the linker working, finished the part of the code generator that wrote the object file, and I could actually compile and link small programs.

Dave: How did the debugger fit into all this?

John: Around August ’93 the project was falling into place, but we still didn’t have a source-level debugger. In a most serendipitous event, Dan Podwall, a friend of mine from Symantec, called and asked whether there were any opportunities at Metrowerks. Greg Galanos called him right away, hired him on the phone, and 4 weeks later he had written a debugger - in PowerPlant, no less - that could single-step and set breakpoints. This would be the first commercial PowerPlant program - in fact, the first PowerPlant program of any kind aside from Greg Dow’s demos.

Dave: How did you build the compiler?

John: By September ’93 we had some prototype PowerPC hardware, and I had a working code generator and linker which ran on the 68K Macintosh and generated PEF executables that ran on the prototypes. Since this compiler was already built using our own 68K compiler, it was pretty easy to rehost it on the Power Macintosh: we made the changes for the Universal Headers and routine descriptors and such, then compiled it with itself on the 68K machine, which gave us (after some debugging!) a working PowerPC-hosted PowerPC compiler. With a little bit of trickery, mandated by differences between PowerPC floating-point hardware and the 68K SANE software floating-point architecture, we were able to rehost the 68K compiler on the Power Macintosh as well. We now had the fastest compilers on the Macintosh.

Dave: What next?

John: I still had a lot of work to do on the PowerPC code generator. The biggest task was to replace the quick-and-dirty register allocator with a graph coloring-based allocator. This is one of the great algorithms in the history of compilers. For years people had been trying to come up with an accurate way to represent the lifetimes of variables, so that variables or temporaries that did not overlap could share a register. A lot of ad hoc techniques were developed, but this guy from IBM Watson Research Center named Greg Chaitin discovered a formal approach that solved the problem better than anything that had been previously attempted: build an “interference graph” which has an edge between any two variables whose values may be live at the same time, and then try to color this graph with N colors where N is the number of available registers.

So my code generator assumes it has an infinite number of “virtual” registers, and generates the most efficient code it can under that assumption; for example, it assumes that all local variables, arguments, and TOC pointers can be assigned to a register. After the code is all generated, the register allocator tries to rewrite the virtual registers using real PowerPC registers, and generates extra code to “spill” values that couldn’t get a real register. In most cases, everything gets a register since there are so many on the PowerPC. The smarter register allocator probably makes the overall largest contribution to code quality.

The algorithm has one drawback: it has O(N^2) complexity. There are actually programs which have so many intermediate expressions that the interference graph gets too large and it takes several minutes to color it. So I had to keep around the quick-and-dirty allocator as well, which is why you’ll sometimes get an annoying message that says the code generator ran out of registers if you’re compiling without global optimizations.

Dave: And so, CodeWarrior was born!

John: By December I had pretty much everything working. After a last-minute dash to get C++ language support working on the PowerPC, we were able to burn our first public release, DR/1, starting a long Metrowerks tradition of getting things in under the wire and never missing a ship date. We introduced the product at the San Francisco Macworld Expo with our huge 8-page MacWeek advertisement, and CodeWarrior™ was born.

There were plenty of things to be cleaned up between DR/1 and DR/3, which was our real “1.0” release. But by shipping DR/1 and DR/2 when we did, and by working closely with a lot of the major Macintosh software vendors, we were able to help a lot of companies get their software ported to the PowerMac that otherwise might not have.

For me, I had accomplished what I had wanted to when I was back at Symantec: building the PowerPC compiler that most users would use to port their code to the new Power Macintoshes. And Greg had kept his promise and given me my dream job.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Capto 1.2.9 - $29.99
Capto (was Voila) is an easy-to-use app that takes capturing, recording, video and image editing to the next level. With an intelligent file manager and quick sharing options, Capto is perfect for... Read more
Opera 51.0.2830.40 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
GarageSale 7.0.13 - Create outstanding e...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
1Password 6.8.7 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Evernote 7.0.1 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
MacUpdate Desktop 6.2.0 - $20.00
MacUpdate Desktop brings seamless 1-click app installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on... Read more
HoudahSpot 4.3.5 - Advanced file-search...
HoudahSpot is a versatile desktop search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the... Read more
EtreCheck 4.0.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
WhatsApp 0.2.8361 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
iClock 4.2 - Customize your menubar cloc...
iClock is a menu-bar replacement for Apple's default clock but with 100x features. Have your Apple or Google calendar in the menubar. Have the day, date, and time in different fonts and colors in the... Read more

Latest Forum Discussions

See All

Alto's Odyssey Guide - How to Tackl...
Alto’s Odyssey is a completely stunning and serene runner, but it can also be a bit tricky. Check out these to try and keep your cool while playing this endless runner: Don’t focus too much on tasks [Read more] | Read more »
Here's everything you need to know...
Alto's Odyssey is a really, really good game. If you don't believe me, you should definitely check out our review by clicking this link right here. It takes the ideas from the original Alto's Adventure, then subtly builds on them, creating... | Read more »
Alto's Odyssey (Games)
Alto's Odyssey 1.0.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: Just beyond the horizon sits a majestic desert, vast and unexplored. Join Alto and his friends and set off on an endless... | Read more »
Vainglory 5v5: Everything you need to kn...
Vainglory just got bigger. [Read more] | Read more »
Check out these 5 games that are a lot l...
So you're in love with Minecraft, but you're looking for something else to play as well? You've come to the right place then, because this list is all about games that are a bit like Minecraft. Some of them, more than others. [Read more] | Read more »
Our top 5 characters from casual RPG Cre...
Creature Quest definitely lives up to its name with a host of collectible creatures based on fantasy tales and world mythologies. To celebrate Creature Quest’s first birthday, we’re going to lay out what we think are the five best characters in the... | Read more »
Around the Empire: What have you missed...
Did you know that Steel Media has a whole swathe of other sites dedicated to all aspects of mobile gaming? Sure you'll get the very best iPhone news, reviews, and opinions right here at 148Apps, but we don't want you missing out on a single piece... | Read more »
All the best games on sale for iPhone an...
Oh hi there, and welcome to our round-up of the best games that are currently on sale for iPhone and iPad. You thought I didn't see you there, did you, skulking behind the bushes? Trust me though, the bushes aren't where the best deals are. The... | Read more »
The Battle of Polytopia Guide - How to H...
A new update just released for The Battle of Polytopia (formerly Super Tribes), which introduces online multiplayer. For all the fans of Midjiwan’s lite take on Civilization, this is certainly welcome news, but playing online isn’t as easy and... | Read more »
The best games that came out for iPhone...
Another week, another bunch of new releases on the App Store, another update to our big list of new games. It's not a classic lineup this week, but there are some really good ones in the mix all the same. [Read more] | Read more »

Price Scanner via MacPrices.net

Amazon restocks MacBook Pros with models avai...
Amazon has restocked 15″ and 13″ Apple MacBook Pros with models on sale for up to $251 off MSRP. Shipping is free. Note that stock of some Macs may come and go (and some sell out quickly), so check... Read more
Lowest price of the year: 15″ 2.8GHz Apple Ma...
Amazon has the 2017 Space Gray 15″ 2.8GHz MacBook Pro on sale today for $251 off MSRP. Shipping is free: – 15″ 2.8GHz Touch Bar MacBook Pro Space Gray (MPTR2LL/A): $2148, $251 off MSRP Their price is... Read more
Apple restocks full line of Certified Refurbi...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
Lowest sale price available for 13″ 1.8GHz Ma...
Focus Camera has the 2017 13″ 1.8GHz/128GB Apple MacBook Air on sale today for $829 including free shipping. Their price is $170 off MSRP, and it’s the lowest price available for a current 13″... Read more
21-inch 2.3GHz iMac on sale for $999, $100 of...
B&H Photo has the 2017 21″ 2.3GHz iMac (MMQA2LL/A) in stock and on sale for $999 including free shipping plus NY & NJ tax only. Their price is $100 off MSRP. Read more
Apple refurbished Mac minis in stock again st...
Apple has restocked Certified Refurbished Mac minis starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: – 1.4GHz Mac mini: $419 $80 off MSRP – 2.6GHz Mac... Read more
Tuesday MacBook Deals: $250 off 15″ 2.9GHz Ma...
Adorama has the Silver 15″ 2.9GHz Apple MacBook Pro on sale today for $250 off MSRP. Shipping is free, and Adorama charges sales tax for residents in NY & NJ only: – 15″ 2.9GHz Silver MacBook Pro... Read more
Save up to $350 with these Apple Certified Re...
Apple has a full line of Certified Refurbished iMacs available for up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: – 27... Read more
B&H offers $200 discount on Silver 15″ Ma...
B&H Photo has Silver 15″ Apple MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 15″ 2.8GHz Touch Bar MacBook Pro Silver (... Read more
12″ Apple iPad Pro Sale of the Year! Models u...
B&H Photo has 12″ #iPad Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 12″ 64GB WiFi iPad Pro: $719 $80 off MSRP – 12″ 256GB WiFi... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 113523441 Orange, CA, California, United States Posted: 21-Feb-2018 Weekly Hours: 40.00 **Job Summary** Are you passionate Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Sr. Experience Designer, Today at *Apple* -...
# Sr. Experience Designer, Today at Apple Job Number: 56495251 Santa Clara Valley, California, United States Posted: 18-Jan-2018 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.