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

Printopia 2.1.14 - Share Mac printers wi...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
Google Drive 1.24 - File backup and shar...
Google Drive is a place where you can create, share, collaborate, and keep all of your stuff. Whether you're working with a friend on a joint research project, planning a wedding with your fiancé, or... Read more
Chromium 45.0.2454.85 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 45.0.2454.85: Note: Does not contain the "... Read more
OmniFocus 2.2.5 - GTD task manager with...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
iFFmpeg 5.7.1 - Convert multimedia files...
iFFmpeg is a graphical front-end for FFmpeg, a command-line tool used to convert multimedia files between formats. The command line instructions can be very hard to master/understand, so iFFmpeg does... Read more
VOX 2.6 - Music player that supports man...
VOX is a beautiful music player that supports many filetypes. The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all... Read more
Box Sync 4.0.6567 - Online synchronizati...
Box Sync gives you a hard-drive in the Cloud for online storage. Note: You must first sign up to use Box. What if the files you need are on your laptop -- but you're on the road with your iPhone? No... Read more
Carbon Copy Cloner 4.1.4 - Easy-to-use b...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
OmniGraffle Pro 6.3.1 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
Monosnap 3.1.2 - Versatile screenshot ut...
Monosnap lets you capture screenshots, share files, and record video and .gifs! Capture: Capture full screen, just part of the screen, or a selected window Make your crop area pixel perfect with... Read more

Goat Simulator MMO Simulator (Games)
Goat Simulator MMO Simulator 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** Coffee Stain Studios brings next-gen... | Read more »
Worms™ 4 (Games)
Worms™ 4 1.02 Device: iOS Universal Category: Games Price: $4.99, Version: 1.02 (iTunes) Description: The latest instalment in the worldwide mega hit franchise! Coming soon to iPhone, iPad and iPod touch. When the guys and girls at... | Read more »
The Deer God (Games)
The Deer God 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: 30% off launch sale!!! “It can be a struggle, but it's all worth it when you're shooting fire out your antlers.” Kotaku “The... | Read more »
AppSpy's Patreon campaign kicks off
Occasionally you'll see us use AppSpy's videos here on 148Apps to support an article we've written. That's because we're part of Steel Media, and AppSpy is Steel's video arm, so we're all part of one happy family. [Read more] | Read more »
We're Sorry to Report that Moonrise...
Moonrise is a very promising-looking, Pokemon-esque monster collecting and battling game that we were really looking forward to reviewing, but unfortunately it looks like that's never going to happen. [Read more] | Read more »
The Latest Update for The Sims FreePlay...
Commerce has gotten a little more active with the newest update for The Sims FreePlay, making Sunset Mall more of a hangout than ever before. [Read more] | Read more »
This Week at 148Apps: August 24-28, 2015
The Apps of August With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
NASCAR in Real Racing 3? Sure, Why Not?
I have to give Firemonkeys credit - it's very cool of them to add NASCAR to Real Racing 3 via an update rather than making a separate game for it. But that's a different discussion for another time; for now let's sit back and enjoy driving in... | Read more »
The nuyu is an Inexpensive Activity Moni...
Today, Health o Meter nuyu has announced a series of health and fitness-related products, including the aforementioned activity monitor along with a wireless scale. All at a decent pricepoint, no less. [Read more] | Read more »
The Makers of Overkill are Trying Someth...
Craneballs, the studio responsible for the Overkill series, is taking a little break from all that violence (a little break) to bring us Cube Worm - a 3D take on one of the most classic PC/calculator games in existence. [Read more] | Read more »

Price Scanner via MacPrices.net

Will You Buy An iPad Pro? – The ‘Book Mystiqu...
It looks like we may not have to wait much longer to see what finally materializes as a new, larger-panel iPad (Pro/Plus?) Usually reliable Apple product prognosticator KGI Securities analyst Ming-... Read more
eFileCabinet Announces SMB Document Managemen...
Electronic document management (EDM) eFileCabinet, Inc., a hosted solutions provider for small to medium businesses, has announced that its SecureDrawer and eFileCabinet Online services will be... Read more
WaterField Designs Unveils American-Made, All...
San Francisco’s WaterField Designs today unveiled their all-leather Cozmo 2.0 — an elegant attach laptop bag with carefully-designed features to suit any business environment. The Cozmo 2.0 is... Read more
Apple’s 2015 Back to School promotion: Free B...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
128GB MacBook Airs on sale for $100 off MSRP,...
B&H Photo has 11″ & 13″ MacBook Airs with 128GB SSDs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/128GB MacBook Air: $799.99, $100 off MSRP... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
27-inch 3.2GHz iMac on sale for $1679, save $...
B&H Photo has the 27″ 3.2GHz iMac on sale for $1679.99 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Read more
Apple and Cisco Partner to Deliver Fast-Lane...
Apple and Cisco have announced a partnership to create a “fast lane” for iOS business users by optimizing Cisco networks for iOS devices and apps. The alliance integrates iPhone with Cisco enterprise... Read more
Apple offering refurbished 2015 13-inch Retin...
The Apple Store is offering Apple Certified Refurbished 2015 13″ Retina MacBook Pros for up to $270 (15%) off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Apple refurbished 2015 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2015 11″ and 13″ MacBook Airs (the latest models), available for up to $180 off the cost of new models. An Apple one-year warranty is included with... Read more

Jobs Board

*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
Simply Mac *Apple* Specialist- Repair Techn...
Simply Mac is the greatest premier retailer of Apple products expertise in North America. We're looking for dedicated individuals to provide personalized service and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the greatest premier retailer of Apple products expertise in North America. We're looking for dedicated individuals to provide personalized service and Read more
*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
Simply Mac- *Apple* Specialist- Store Manag...
Simply Mac is the largest premier retailer for Apple products and solutions. We're looking for dedicated individuals with a passion to simplify and enhance the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.