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-WEBVTT
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- The following is a conversation with Chris Latner.
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- Currently, he's a senior director of Google working
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- on several projects, including CPU, GPU, TPU accelerators
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- for TensorFlow, Swift for TensorFlow,
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- and all kinds of machine learning compiler magic
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- going on behind the scenes.
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- He's one of the top experts in the world
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- on compiler technologies, which means
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- he deeply understands the intricacies of how
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- hardware and software come together
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- to create efficient code.
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- He created the LLVM compiler infrastructure project
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- and the Clang compiler.
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- He led major engineering efforts at Apple,
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- including the creation of the Swift programming language.
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- He also briefly spent time at Tesla as vice president
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- of autopilot software during the transition from autopilot
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- hardware one to hardware two, when Tesla essentially
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- started from scratch to build an in house software
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- infrastructure for autopilot.
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- I could have easily talked to Chris for many more hours.
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- Compiling code down across the level's abstraction
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- is one of the most fundamental and fascinating aspects
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- of what computers do, and he is one of the world experts
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- in this process.
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- It's rigorous science, and it's messy, beautiful art.
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- This conversation is part of the Artificial Intelligence
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- podcast.
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- If you enjoy it, subscribe on YouTube,
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- iTunes, or simply connect with me on Twitter
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- at Lex Friedman, spelled F R I D. And now, here's
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- my conversation with Chris Ladner.
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- What was the first program you've ever written?
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- My first program back.
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- And when was it?
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- I think I started as a kid, and my parents
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- got a basic programming book.
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- And so when I started, it was typing out programs from a book
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- and seeing how they worked, and then typing them in wrong
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- and trying to figure out why they were not working right,
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- and that kind of stuff.
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- So basic, what was the first language
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- that you remember yourself maybe falling in love with,
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- like really connecting with?
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- I don't know.
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- I mean, I feel like I've learned a lot along the way,
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- and each of them have a different, special thing about them.
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- So I started in basic, and then went like GW basic, which
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- was the thing back in the DOS days,
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- and then upgraded to Q basic, and eventually Quick basic,
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- which are all slightly more fancy versions
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- of Microsoft basic, made the jump to Pascal,
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- and started doing machine language programming and assembly
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- in Pascal, which was really cool.
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- Turbo Pascal was amazing for its day.
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- Eventually, gone to C, C++, and then kind of did
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- lots of other weird things.
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- I feel like you took the dark path, which is the,
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- you could have gone Lisp, you could have gone a higher level
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- sort of functional, philosophical, hippie route.
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- Instead, you went into like the dark arts of the C.
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- It was straight into the machine.
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- Straight into the machine.
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- So started with basic Pascal and then assembly,
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- and then wrote a lot of assembly, and eventually did
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- small talk and other things like that,
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- but that was not the starting point.
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- But so what is this journey to see?
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- Is that in high school?
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- Is that in college?
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- That was in high school, yeah.
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- So, and then that was really about trying
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- to be able to do more powerful things than what Pascal
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- could do and also to learn a different world.
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- So he was really confusing to me with pointers
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- and the syntax and everything, and it took a while,
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- but Pascal's much more principled in various ways,
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- sees more, I mean, it has its historical roots,
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- but it's not as easy to learn.
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- With pointers, there's this memory management thing
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- that you have to become conscious of.
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- Is that the first time you start to understand
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- that there's resources that you're supposed to manage?
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- Well, so you have that in Pascal as well,
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- but in Pascal, the carrot instead of the star,
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- there's some small differences like that,
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- but it's not about pointer arithmetic.
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- And see, you end up thinking about how things get laid
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- out in memory a lot more.
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- And so in Pascal, you have allocating and deallocating
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- and owning the memory, but just the programs are simpler
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- and you don't have to, well, for example,
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- Pascal has a string type.
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- And so you can think about a string
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- instead of an array of characters
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- which are consecutive in memory.
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- So it's a little bit of a higher level abstraction.
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- So let's get into it.
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- Let's talk about LLVM, Selang, and compilers.
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- Sure.
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- So can you tell me first what LLVM and Selang are,
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- and how is it that you find yourself the creator
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- and lead developer, one of the most powerful
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- compiler optimization systems in use today?
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- Sure, so I guess they're different things.
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- So let's start with what is a compiler?
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- Is that a good place to start?
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- What are the phases of a compiler?
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- Where are the parts?
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- Yeah, what is it?
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- So what is even a compiler used for?
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- So the way I look at this is you have a two sided problem
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- of you have humans that need to write code.
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- And then you have machines that need to run the program
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- that the human wrote.
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- And for lots of reasons, the humans don't want to be
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- writing in binary and want to think about every piece
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- of hardware.
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- So at the same time that you have lots of humans,
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- you also have lots of kinds of hardware.
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- And so compilers are the art of allowing humans
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- to think at a level of abstraction
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- that they want to think about.
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- And then get that program, get the thing that they wrote
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- to run on a specific piece of hardware.
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- And the interesting and exciting part of all this
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- is that there's now lots of different kinds of hardware,
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- chips like x86 and PowerPC and ARM and things like that,
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- but also high performance accelerators for machine
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- learning and other things like that are also just different
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- kinds of hardware, GPUs, these are new kinds of hardware.
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- And at the same time on the programming side of it,
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- you have basic, you have C, you have JavaScript,
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- you have Python, you have Swift, you have like lots
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- of other languages that are all trying to talk to the human
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- in a different way to make them more expressive
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- and capable and powerful.
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- And so compilers are the thing that goes from one
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- to the other now.
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- And to end from the very beginning to the very end.
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- And to end, and so you go from what the human wrote
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- and programming languages end up being about expressing intent,
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- not just for the compiler and the hardware,
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- but the programming language's job is really to capture
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- an expression of what the programmer wanted
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- that then can be maintained and adapted
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- and evolved by other humans, as well as by the,
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- interpreted by the compiler.
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- So when you look at this problem,
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- you have on the one hand humans, which are complicated,
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- you have hardware, which is complicated.
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-06:36.720 --> 06:39.880
- And so compilers typically work in multiple phases.
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- And so the software engineering challenge
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- that you have here is try to get maximum reuse
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- out of the amount of code that you write
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- because these compilers are very complicated.
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- And so the way it typically works out is that
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- you have something called a front end or a parser
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- that is language specific.
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- And so you'll have a C parser, that's what Clang is,
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- or C++ or JavaScript or Python or whatever,
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- that's the front end.
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- Then you'll have a middle part,
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- which is often the optimizer.
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- And then you'll have a late part,
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- which is hardware specific.
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- And so compilers end up, there's many different layers often,
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- but these three big groups are very common in compilers.
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- And what LLVM is trying to do is trying to standardize
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- that middle and last part.
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- And so one of the cool things about LLVM
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- is that there are a lot of different languages
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- that compile through to it.
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- And so things like Swift, but also Julia, Rust,
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- Clang for C, C++, Subjective C,
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- like these are all very different languages
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- and they can all use the same optimization infrastructure,
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- which gets better performance,
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- and the same code generation infrastructure
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- for hardware support.
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- And so LLVM is really that layer that is common,
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- that all these different specific compilers can use.
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- And is it a standard, like a specification,
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- or is it literally an implementation?
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- It's an implementation.
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- And so it's, I think there's a couple of different ways
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- of looking at it, right?
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- Because it depends on which angle you're looking at it from.
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- LLVM ends up being a bunch of code, okay?
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- So it's a bunch of code that people reuse
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- and they build compilers with.
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- We call it a compiler infrastructure
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- because it's kind of the underlying platform
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- that you build a concrete compiler on top of.
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- But it's also a community.
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- And the LLVM community is hundreds of people
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- that all collaborate.
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- And one of the most fascinating things about LLVM
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- over the course of time is that we've managed somehow
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- to successfully get harsh competitors
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- in the commercial space to collaborate
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- on shared infrastructure.
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- And so you have Google and Apple.
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- You have AMD and Intel.
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- You have NVIDIA and AMD on the graphics side.
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- You have Cray and everybody else doing these things.
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- And like all these companies are collaborating together
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- to make that shared infrastructure
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- really, really great.
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- And they do this not out of the goodness of their heart
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- but they do it because it's in their commercial interest
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- of having really great infrastructure
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- that they can build on top of.
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- And facing the reality that it's so expensive
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- that no one company, even the big companies,
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- no one company really wants to implement it all themselves.
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- Expensive or difficult?
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- Both.
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-09:16.960 --> 09:20.600
- That's a great point because it's also about the skill sets.
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- And these, the skill sets are very hard to find.
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- How big is the LLVM?
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- It always seems like with open source projects,
-
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- the kind, and LLVM is open source?
-
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- Yes, it's open source.
-
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- It's about, it's 19 years old now.
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- So it's fairly old.
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- It seems like the magic often happens
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- within a very small circle of people.
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- Yes.
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- At least at early birth and whatever.
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- Yes.
-
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- So the LLVM came from a university project.
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- And so I was at the University of Illinois.
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- And there it was myself, my advisor,
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- and then a team of two or three research students
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- in the research group.
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- And we built many of the core pieces initially.
-
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- I then graduated and went to Apple.
-
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- And then Apple brought it to the products,
-
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- first in the OpenGL graphics stack,
-
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- but eventually to the C compiler realm
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- and eventually built Clang
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-10:12.760 --> 10:14.640
- and eventually built Swift and these things.
-
-10:14.640 --> 10:16.360
- Along the way, building a team of people
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-10:16.360 --> 10:18.600
- that are really amazing compiler engineers
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- that helped build a lot of that.
-
-10:20.120 --> 10:21.840
- And so as it was gaining momentum
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- and as Apple was using it, being open source and public
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- and encouraging contribution, many others,
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- for example, at Google, came in and started contributing.
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-10:30.400 --> 10:33.680
- And in some cases, Google effectively owns Clang now
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- because it cares so much about C++
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- and the evolution of that ecosystem.
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- And so it's investing a lot in the C++ world
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- and the tooling and things like that.
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-10:42.960 --> 10:47.840
- And so likewise, NVIDIA cares a lot about CUDA.
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-10:47.840 --> 10:52.840
- And so CUDA uses Clang and uses LVM for graphics and GPGPU.
-
-10:54.960 --> 10:59.880
- And so when you first started as a master's project, I guess,
-
-10:59.880 --> 11:02.920
- did you think it was gonna go as far as it went?
-
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- Were you crazy ambitious about it?
-
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- No.
-
-11:07.120 --> 11:09.760
- It seems like a really difficult undertaking, a brave one.
-
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- Yeah, no, no, it was nothing like that.
-
-11:11.280 --> 11:13.640
- So I mean, my goal when I went to University of Illinois
-
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- was to get in and out with the non thesis masters
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- in a year and get back to work.
-
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- So I was not planning to stay for five years
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- and build this massive infrastructure.
-
-11:24.440 --> 11:27.400
- I got nerd sniped into staying.
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-11:27.400 --> 11:29.480
- And a lot of it was because LVM was fun
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-11:29.480 --> 11:30.920
- and I was building cool stuff
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-11:30.920 --> 11:33.400
- and learning really interesting things
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-11:33.400 --> 11:36.880
- and facing both software engineering challenges
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-11:36.880 --> 11:38.520
- but also learning how to work in a team
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-11:38.520 --> 11:40.120
- and things like that.
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-11:40.120 --> 11:43.600
- I had worked at many companies as interns before that,
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- but it was really a different thing
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- to have a team of people that were working together
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-11:48.120 --> 11:50.480
- and trying to collaborate in version control
-
-11:50.480 --> 11:52.400
- and it was just a little bit different.
-
-11:52.400 --> 11:54.080
- Like I said, I just talked to Don Knuth
-
-11:54.080 --> 11:56.840
- and he believes that 2% of the world population
-
-11:56.840 --> 11:59.600
- have something weird with their brain, that they're geeks,
-
-11:59.600 --> 12:02.560
- they understand computers, they're connected with computers.
-
-12:02.560 --> 12:04.360
- He put it at exactly 2%.
-
-12:04.360 --> 12:05.560
- Okay, so...
-
-12:05.560 --> 12:06.560
- Is this a specific act?
-
-12:06.560 --> 12:08.760
- It's very specific.
-
-12:08.760 --> 12:10.200
- Well, he says, I can't prove it,
-
-12:10.200 --> 12:11.800
- but it's very empirically there.
-
-12:13.040 --> 12:14.480
- Is there something that attracts you
-
-12:14.480 --> 12:16.920
- to the idea of optimizing code?
-
-12:16.920 --> 12:19.120
- And he seems like that's one of the biggest,
-
-12:19.120 --> 12:20.920
- coolest things about LVM.
-
-12:20.920 --> 12:22.480
- Yeah, that's one of the major things it does.
-
-12:22.480 --> 12:26.440
- So I got into that because of a person, actually.
-
-12:26.440 --> 12:28.200
- So when I was in my undergraduate,
-
-12:28.200 --> 12:32.040
- I had an advisor or a professor named Steve Vegdahl
-
-12:32.040 --> 12:35.760
- and I went to this little tiny private school.
-
-12:35.760 --> 12:38.280
- There were like seven or nine people
-
-12:38.280 --> 12:40.320
- in my computer science department,
-
-12:40.320 --> 12:43.080
- students in my class.
-
-12:43.080 --> 12:47.440
- So it was a very tiny, very small school.
-
-12:47.440 --> 12:49.960
- It was kind of a work on the side of the math department
-
-12:49.960 --> 12:51.240
- kind of a thing at the time.
-
-12:51.240 --> 12:53.800
- I think it's evolved a lot in the many years since then,
-
-12:53.800 --> 12:58.280
- but Steve Vegdahl was a compiler guy
-
-12:58.280 --> 12:59.600
- and he was super passionate
-
-12:59.600 --> 13:02.720
- and his passion rubbed off on me
-
-13:02.720 --> 13:04.440
- and one of the things I like about compilers
-
-13:04.440 --> 13:09.120
- is that they're large, complicated software pieces.
-
-13:09.120 --> 13:12.920
- And so one of the culminating classes
-
-13:12.920 --> 13:14.520
- that many computer science departments
-
-13:14.520 --> 13:16.680
- at least at the time did was to say
-
-13:16.680 --> 13:18.400
- that you would take algorithms and data structures
-
-13:18.400 --> 13:19.480
- and all these core classes,
-
-13:19.480 --> 13:20.720
- but then the compilers class
-
-13:20.720 --> 13:22.160
- was one of the last classes you take
-
-13:22.160 --> 13:24.360
- because it pulls everything together
-
-13:24.360 --> 13:27.000
- and then you work on one piece of code
-
-13:27.000 --> 13:28.680
- over the entire semester.
-
-13:28.680 --> 13:32.080
- And so you keep building on your own work,
-
-13:32.080 --> 13:34.800
- which is really interesting and it's also very challenging
-
-13:34.800 --> 13:37.520
- because in many classes, if you don't get a project done,
-
-13:37.520 --> 13:39.320
- you just forget about it and move on to the next one
-
-13:39.320 --> 13:41.320
- and get your B or whatever it is,
-
-13:41.320 --> 13:43.880
- but here you have to live with the decisions you make
-
-13:43.880 --> 13:45.280
- and continue to reinvest in it.
-
-13:45.280 --> 13:46.880
- And I really like that.
-
-13:46.880 --> 13:51.080
- And so I did a extra study project with him
-
-13:51.080 --> 13:53.960
- the following semester and he was just really great
-
-13:53.960 --> 13:56.920
- and he was also a great mentor in a lot of ways.
-
-13:56.920 --> 13:59.560
- And so from him and from his advice,
-
-13:59.560 --> 14:01.520
- he encouraged me to go to graduate school.
-
-14:01.520 --> 14:03.200
- I wasn't super excited about going to grad school.
-
-14:03.200 --> 14:05.240
- I wanted the master's degree,
-
-14:05.240 --> 14:07.440
- but I didn't want to be an academic.
-
-14:09.000 --> 14:11.160
- But like I said, I kind of got tricked into saying
-
-14:11.160 --> 14:14.560
- I was having a lot of fun and I definitely do not regret it.
-
-14:14.560 --> 14:15.840
- Well, the aspects of compilers
-
-14:15.840 --> 14:17.960
- were the things you connected with.
-
-14:17.960 --> 14:22.120
- So LVM, there's also the other part
-
-14:22.120 --> 14:23.440
- that's just really interesting
-
-14:23.440 --> 14:27.640
- if you're interested in languages is parsing and just analyzing
-
-14:27.640 --> 14:29.640
- like, yeah, analyzing the language,
-
-14:29.640 --> 14:31.240
- breaking it down, parsing and so on.
-
-14:31.240 --> 14:32.280
- Was that interesting to you
-
-14:32.280 --> 14:34.080
- or were you more interested in optimization?
-
-14:34.080 --> 14:37.400
- For me, it was more, so I'm not really a math person.
-
-14:37.400 --> 14:39.600
- I can do math, I understand some bits of it
-
-14:39.600 --> 14:41.600
- when I get into it,
-
-14:41.600 --> 14:43.960
- but math is never the thing that attracted me.
-
-14:43.960 --> 14:46.160
- And so a lot of the parser part of the compiler
-
-14:46.160 --> 14:48.960
- has a lot of good formal theories that Dawn, for example,
-
-14:48.960 --> 14:50.440
- knows quite well.
-
-14:50.440 --> 14:51.920
- Still waiting for his book on that.
-
-14:51.920 --> 14:56.080
- But I just like building a thing
-
-14:56.080 --> 14:59.200
- and seeing what it could do and exploring
-
-14:59.200 --> 15:00.800
- and getting it to do more things
-
-15:00.800 --> 15:02.880
- and then setting new goals and reaching for them.
-
-15:02.880 --> 15:08.880
- And in the case of LVM, when I started working on that,
-
-15:08.880 --> 15:13.360
- my research advisor that I was working for was a compiler guy.
-
-15:13.360 --> 15:15.600
- And so he and I specifically found each other
-
-15:15.600 --> 15:16.920
- because we both interested in compilers
-
-15:16.920 --> 15:19.480
- and so I started working with them and taking his class.
-
-15:19.480 --> 15:21.800
- And a lot of LVM initially was it's fun
-
-15:21.800 --> 15:23.560
- implementing all the standard algorithms
-
-15:23.560 --> 15:26.360
- and all the things that people had been talking about
-
-15:26.360 --> 15:28.920
- and were well known and they were in the curricula
-
-15:28.920 --> 15:31.320
- for advanced studies in compilers.
-
-15:31.320 --> 15:34.560
- And so just being able to build that was really fun
-
-15:34.560 --> 15:36.160
- and I was learning a lot
-
-15:36.160 --> 15:38.640
- by instead of reading about it, just building.
-
-15:38.640 --> 15:40.200
- And so I enjoyed that.
-
-15:40.200 --> 15:42.800
- So you said compilers are these complicated systems.
-
-15:42.800 --> 15:47.240
- Can you even just with language try to describe
-
-15:48.240 --> 15:52.240
- how you turn a C++ program into code?
-
-15:52.240 --> 15:53.480
- Like what are the hard parts?
-
-15:53.480 --> 15:54.640
- Why is it so hard?
-
-15:54.640 --> 15:56.840
- So I'll give you examples of the hard parts along the way.
-
-15:56.840 --> 16:01.040
- So C++ is a very complicated programming language.
-
-16:01.040 --> 16:03.480
- It's something like 1,400 pages in the spec.
-
-16:03.480 --> 16:06.120
- So C++ by itself is crazy complicated.
-
-16:06.120 --> 16:07.160
- Can we just, sorry, pause.
-
-16:07.160 --> 16:08.720
- What makes the language complicated
-
-16:08.720 --> 16:11.520
- in terms of what's syntactically?
-
-16:11.520 --> 16:14.320
- Like, so it's what they call syntax.
-
-16:14.320 --> 16:16.280
- So the actual how the characters are arranged.
-
-16:16.280 --> 16:20.080
- Yes, it's also semantics, how it behaves.
-
-16:20.080 --> 16:21.720
- It's also in the case of C++.
-
-16:21.720 --> 16:23.400
- There's a huge amount of history.
-
-16:23.400 --> 16:25.560
- C++ build on top of C.
-
-16:25.560 --> 16:28.720
- You play that forward and then a bunch of suboptimal
-
-16:28.720 --> 16:30.360
- in some cases decisions were made
-
-16:30.360 --> 16:33.400
- and they compound and then more and more and more things
-
-16:33.400 --> 16:35.080
- keep getting added to C++
-
-16:35.080 --> 16:37.040
- and it will probably never stop.
-
-16:37.040 --> 16:39.440
- But the language is very complicated from that perspective.
-
-16:39.440 --> 16:41.200
- And so the interactions between subsystems
-
-16:41.200 --> 16:42.360
- is very complicated.
-
-16:42.360 --> 16:43.560
- There's just a lot there.
-
-16:43.560 --> 16:45.640
- And when you talk about the front end,
-
-16:45.640 --> 16:48.560
- one of the major challenges which playing as a project,
-
-16:48.560 --> 16:52.280
- the C++ compiler that I built, I and many people built.
-
-16:53.320 --> 16:57.560
- One of the challenges we took on was we looked at GCC.
-
-16:57.560 --> 17:01.120
- I think GCC at the time was like a really good
-
-17:01.120 --> 17:05.320
- industry standardized compiler that had really consolidated
-
-17:05.320 --> 17:06.760
- a lot of the other compilers in the world
-
-17:06.760 --> 17:08.360
- and was a standard.
-
-17:08.360 --> 17:10.640
- But it wasn't really great for research.
-
-17:10.640 --> 17:12.600
- The design was very difficult to work with
-
-17:12.600 --> 17:16.640
- and it was full of global variables and other things
-
-17:16.640 --> 17:18.120
- that made it very difficult to reuse
-
-17:18.120 --> 17:20.400
- in ways that it wasn't originally designed for.
-
-17:20.400 --> 17:22.560
- And so with Clang, one of the things that we wanted to do
-
-17:22.560 --> 17:25.520
- is push forward on better user interface.
-
-17:25.520 --> 17:28.160
- So make error messages that are just better than GCCs.
-
-17:28.160 --> 17:29.920
- And that's actually hard because you have to do
-
-17:29.920 --> 17:31.880
- a lot of bookkeeping in an efficient way
-
-17:32.800 --> 17:33.640
- to be able to do that.
-
-17:33.640 --> 17:35.160
- We want to make compile time better.
-
-17:35.160 --> 17:37.520
- And so compile time is about making it efficient,
-
-17:37.520 --> 17:38.920
- which is also really hard when you're keeping
-
-17:38.920 --> 17:40.520
- track of extra information.
-
-17:40.520 --> 17:43.400
- We wanted to make new tools available.
-
-17:43.400 --> 17:46.400
- So refactoring tools and other analysis tools
-
-17:46.400 --> 17:48.400
- that the GCC never supported,
-
-17:48.400 --> 17:51.160
- also leveraging the extra information we kept,
-
-17:52.200 --> 17:54.080
- but enabling those new classes of tools
-
-17:54.080 --> 17:55.960
- that then get built into IDEs.
-
-17:55.960 --> 17:58.560
- And so that's been one of the areas
-
-17:58.560 --> 18:01.320
- that Clang has really helped push the world forward in
-
-18:01.320 --> 18:05.080
- is in the tooling for C and C++ and things like that.
-
-18:05.080 --> 18:07.760
- But C++ in the front end piece is complicated
-
-18:07.760 --> 18:09.040
- and you have to build syntax trees
-
-18:09.040 --> 18:11.360
- and you have to check every rule in the spec
-
-18:11.360 --> 18:14.000
- and you have to turn that back into an error message
-
-18:14.000 --> 18:16.040
- to the human that the human can understand
-
-18:16.040 --> 18:17.840
- when they do something wrong.
-
-18:17.840 --> 18:20.760
- But then you start doing what's called lowering.
-
-18:20.760 --> 18:23.440
- So going from C++ in the way that it represents code
-
-18:23.440 --> 18:24.960
- down to the machine.
-
-18:24.960 --> 18:25.800
- And when you do that,
-
-18:25.800 --> 18:28.240
- there's many different phases you go through.
-
-18:29.640 --> 18:33.040
- Often there are, I think LVM has something like 150
-
-18:33.040 --> 18:36.240
- different, what are called passes in the compiler
-
-18:36.240 --> 18:38.760
- that the code passes through
-
-18:38.760 --> 18:41.880
- and these get organized in very complicated ways,
-
-18:41.880 --> 18:44.360
- which affect the generated code and the performance
-
-18:44.360 --> 18:46.000
- and compile time and many of the things.
-
-18:46.000 --> 18:47.320
- What are they passing through?
-
-18:47.320 --> 18:51.840
- So after you do the Clang parsing,
-
-18:51.840 --> 18:53.960
- what's the graph?
-
-18:53.960 --> 18:54.800
- What does it look like?
-
-18:54.800 --> 18:55.960
- What's the data structure here?
-
-18:55.960 --> 18:59.040
- Yeah, so in the parser, it's usually a tree
-
-18:59.040 --> 19:01.040
- and it's called an abstract syntax tree.
-
-19:01.040 --> 19:04.560
- And so the idea is you have a node for the plus
-
-19:04.560 --> 19:06.800
- that the human wrote in their code
-
-19:06.800 --> 19:09.000
- or the function call, you'll have a node for call
-
-19:09.000 --> 19:11.840
- with the function that they call in the arguments they pass.
-
-19:11.840 --> 19:12.680
- Things like that.
-
-19:14.440 --> 19:16.840
- This then gets lowered into what's called
-
-19:16.840 --> 19:18.600
- an intermediate representation
-
-19:18.600 --> 19:22.080
- and intermediate representations are like LVM has one.
-
-19:22.080 --> 19:26.920
- And there it's a, it's what's called a control flow graph.
-
-19:26.920 --> 19:31.200
- And so you represent each operation in the program
-
-19:31.200 --> 19:34.480
- as a very simple, like this is gonna add two numbers.
-
-19:34.480 --> 19:35.880
- This is gonna multiply two things.
-
-19:35.880 --> 19:37.480
- This maybe we'll do a call,
-
-19:37.480 --> 19:40.280
- but then they get put in what are called blocks.
-
-19:40.280 --> 19:43.600
- And so you get blocks of these straight line operations
-
-19:43.600 --> 19:45.320
- where instead of being nested like in a tree,
-
-19:45.320 --> 19:46.920
- it's straight line operations.
-
-19:46.920 --> 19:47.920
- And so there's a sequence
-
-19:47.920 --> 19:49.760
- in ordering to these operations.
-
-19:49.760 --> 19:51.840
- So within the block or outside the block?
-
-19:51.840 --> 19:53.240
- That's within the block.
-
-19:53.240 --> 19:55.000
- And so it's a straight line sequence of operations
-
-19:55.000 --> 19:55.840
- within the block.
-
-19:55.840 --> 19:57.520
- And then you have branches,
-
-19:57.520 --> 20:00.160
- like conditional branches between blocks.
-
-20:00.160 --> 20:02.760
- And so when you write a loop, for example,
-
-20:04.120 --> 20:07.080
- in a syntax tree, you would have a four node
-
-20:07.080 --> 20:09.080
- like for a four statement in a C like language,
-
-20:09.080 --> 20:10.840
- you'd have a four node.
-
-20:10.840 --> 20:12.200
- And you have a pointer to the expression
-
-20:12.200 --> 20:14.120
- for the initializer, a pointer to the expression
-
-20:14.120 --> 20:15.840
- for the increment, a pointer to the expression
-
-20:15.840 --> 20:18.720
- for the comparison, a pointer to the body.
-
-20:18.720 --> 20:21.040
- Okay, and these are all nested underneath it.
-
-20:21.040 --> 20:22.880
- In a control flow graph, you get a block
-
-20:22.880 --> 20:25.960
- for the code that runs before the loop.
-
-20:25.960 --> 20:27.600
- So the initializer code.
-
-20:27.600 --> 20:30.280
- Then you have a block for the body of the loop.
-
-20:30.280 --> 20:33.760
- And so the body of the loop code goes in there,
-
-20:33.760 --> 20:35.520
- but also the increment and other things like that.
-
-20:35.520 --> 20:37.800
- And then you have a branch that goes back to the top
-
-20:37.800 --> 20:39.840
- and a comparison and a branch that goes out.
-
-20:39.840 --> 20:44.000
- And so it's more of a assembly level kind of representation.
-
-20:44.000 --> 20:46.040
- But the nice thing about this level of representation
-
-20:46.040 --> 20:48.680
- is it's much more language independent.
-
-20:48.680 --> 20:51.880
- And so there's lots of different kinds of languages
-
-20:51.880 --> 20:54.520
- with different kinds of, you know,
-
-20:54.520 --> 20:56.600
- JavaScript has a lot of different ideas
-
-20:56.600 --> 20:58.160
- of what is false, for example,
-
-20:58.160 --> 21:00.760
- and all that can stay in the front end,
-
-21:00.760 --> 21:04.200
- but then that middle part can be shared across all of those.
-
-21:04.200 --> 21:07.520
- How close is that intermediate representation
-
-21:07.520 --> 21:10.280
- to new networks, for example?
-
-21:10.280 --> 21:14.320
- Are they, because everything you describe as a kind of
-
-21:14.320 --> 21:16.080
- a close of a neural network graph,
-
-21:16.080 --> 21:18.920
- are they neighbors or what?
-
-21:18.920 --> 21:20.960
- They're quite different in details,
-
-21:20.960 --> 21:22.480
- but they're very similar in idea.
-
-21:22.480 --> 21:24.000
- So one of the things that normal networks do
-
-21:24.000 --> 21:26.880
- is they learn representations for data
-
-21:26.880 --> 21:29.120
- at different levels of abstraction, right?
-
-21:29.120 --> 21:32.360
- And then they transform those through layers, right?
-
-21:33.920 --> 21:35.680
- So the compiler does very similar things,
-
-21:35.680 --> 21:37.120
- but one of the things the compiler does
-
-21:37.120 --> 21:40.640
- is it has relatively few different representations.
-
-21:40.640 --> 21:42.480
- Where a neural network, often as you get deeper,
-
-21:42.480 --> 21:44.800
- for example, you get many different representations
-
-21:44.800 --> 21:47.400
- and each, you know, layer or set of ops
-
-21:47.400 --> 21:50.200
- is transforming between these different representations.
-
-21:50.200 --> 21:53.080
- In a compiler, often you get one representation
-
-21:53.080 --> 21:55.240
- and they do many transformations to it.
-
-21:55.240 --> 21:59.520
- And these transformations are often applied iteratively.
-
-21:59.520 --> 22:02.920
- And for programmers, they're familiar types of things.
-
-22:02.920 --> 22:06.160
- For example, trying to find expressions inside of a loop
-
-22:06.160 --> 22:07.320
- and pulling them out of a loop.
-
-22:07.320 --> 22:08.560
- So if they execute fairer times
-
-22:08.560 --> 22:10.760
- or find redundant computation
-
-22:10.760 --> 22:15.360
- or find constant folding or other simplifications
-
-22:15.360 --> 22:19.040
- turning, you know, two times X into X shift left by one
-
-22:19.040 --> 22:21.960
- and things like this are all the examples
-
-22:21.960 --> 22:23.360
- of the things that happen.
-
-22:23.360 --> 22:26.200
- But compilers end up getting a lot of theorem proving
-
-22:26.200 --> 22:27.640
- and other kinds of algorithms
-
-22:27.640 --> 22:29.960
- that try to find higher level properties of the program
-
-22:29.960 --> 22:32.320
- that then can be used by the optimizer.
-
-22:32.320 --> 22:35.920
- Cool, so what's like the biggest bang for the buck
-
-22:35.920 --> 22:37.680
- with optimization?
-
-22:37.680 --> 22:38.720
- What's a day?
-
-22:38.720 --> 22:39.560
- Yeah.
-
-22:39.560 --> 22:40.920
- Well, no, not even today.
-
-22:40.920 --> 22:42.800
- At the very beginning, the 80s, I don't know.
-
-22:42.800 --> 22:43.960
- Yeah, so for the 80s,
-
-22:43.960 --> 22:46.440
- a lot of it was things like register allocation.
-
-22:46.440 --> 22:51.000
- So the idea of in a modern, like a microprocessor,
-
-22:51.000 --> 22:52.760
- what you'll end up having is you'll end up having memory,
-
-22:52.760 --> 22:54.320
- which is relatively slow.
-
-22:54.320 --> 22:57.080
- And then you have registers relatively fast,
-
-22:57.080 --> 22:59.920
- but registers, you don't have very many of them.
-
-22:59.920 --> 23:02.600
- Okay, and so when you're writing a bunch of code,
-
-23:02.600 --> 23:04.200
- you're just saying like, compute this,
-
-23:04.200 --> 23:05.520
- put in temporary variable, compute this,
-
-23:05.520 --> 23:07.800
- compute this, put in temporary variable,
-
-23:07.800 --> 23:09.760
- I have a loop, I have some other stuff going on.
-
-23:09.760 --> 23:11.680
- Well, now you're running on an x86,
-
-23:11.680 --> 23:13.920
- like a desktop PC or something.
-
-23:13.920 --> 23:16.160
- Well, it only has, in some cases,
-
-23:16.160 --> 23:18.720
- some modes, eight registers, right?
-
-23:18.720 --> 23:20.800
- And so now the compiler has to choose
-
-23:20.800 --> 23:22.800
- what values get put in what registers,
-
-23:22.800 --> 23:24.840
- at what points in the program.
-
-23:24.840 --> 23:26.480
- And this is actually a really big deal.
-
-23:26.480 --> 23:28.560
- So if you think about, you have a loop,
-
-23:28.560 --> 23:31.640
- an inner loop that executes millions of times maybe.
-
-23:31.640 --> 23:33.600
- If you're doing loads and stores inside that loop,
-
-23:33.600 --> 23:34.920
- then it's gonna be really slow.
-
-23:34.920 --> 23:37.080
- But if you can somehow fit all the values
-
-23:37.080 --> 23:40.200
- inside that loop in registers, now it's really fast.
-
-23:40.200 --> 23:43.400
- And so getting that right requires a lot of work,
-
-23:43.400 --> 23:44.960
- because there's many different ways to do that.
-
-23:44.960 --> 23:47.000
- And often what the compiler ends up doing
-
-23:47.000 --> 23:48.880
- is it ends up thinking about things
-
-23:48.880 --> 23:51.920
- in a different representation than what the human wrote.
-
-23:51.920 --> 23:53.320
- All right, you wrote into x.
-
-23:53.320 --> 23:56.800
- Well, the compiler thinks about that as four different values,
-
-23:56.800 --> 23:58.360
- each which have different lifetimes
-
-23:58.360 --> 24:00.400
- across the function that it's in.
-
-24:00.400 --> 24:02.640
- And each of those could be put in a register
-
-24:02.640 --> 24:05.840
- or memory or different memory, or maybe in some parts
-
-24:05.840 --> 24:08.760
- of the code, recompute it instead of stored and reloaded.
-
-24:08.760 --> 24:10.000
- And there are many of these different kinds
-
-24:10.000 --> 24:11.440
- of techniques that can be used.
-
-24:11.440 --> 24:14.840
- So it's adding almost like a time dimension
-
-24:14.840 --> 24:18.320
- to it's trying to optimize across time.
-
-24:18.320 --> 24:20.360
- So it's considering when you're programming,
-
-24:20.360 --> 24:21.920
- you're not thinking in that way.
-
-24:21.920 --> 24:23.200
- Yeah, absolutely.
-
-24:23.200 --> 24:28.200
- And so the risk era made things, so risk chips, RISC,
-
-24:28.200 --> 24:33.200
- RISC, the risk chips as opposed to SISC chips,
-
-24:33.680 --> 24:36.000
- the risk chips made things more complicated
-
-24:36.000 --> 24:39.720
- for the compiler because what they ended up doing
-
-24:39.720 --> 24:42.360
- is ending up adding pipelines to the processor
-
-24:42.360 --> 24:45.000
- where the processor can do more than one thing at a time.
-
-24:45.000 --> 24:47.600
- But this means that the order of operations matters a lot.
-
-24:47.600 --> 24:49.720
- And so one of the classical compiler techniques
-
-24:49.720 --> 24:52.000
- that you use is called scheduling.
-
-24:52.000 --> 24:54.200
- And so moving the instructions around
-
-24:54.200 --> 24:57.400
- so that the processor can like keep its pipelines full
-
-24:57.400 --> 24:59.600
- instead of stalling and getting blocked.
-
-24:59.600 --> 25:00.960
- And so there's a lot of things like that
-
-25:00.960 --> 25:03.600
- that are kind of bread and butter or compiler techniques
-
-25:03.600 --> 25:06.240
- that have been studied a lot over the course of decades now.
-
-25:06.240 --> 25:08.520
- But the engineering side of making them real
-
-25:08.520 --> 25:10.680
- is also still quite hard.
-
-25:10.680 --> 25:12.400
- And you talk about machine learning,
-
-25:12.400 --> 25:14.400
- this is a huge opportunity for machine learning
-
-25:14.400 --> 25:16.520
- because many of these algorithms
-
-25:16.520 --> 25:19.120
- are full of these like hokey hand rolled heuristics
-
-25:19.120 --> 25:20.880
- which work well on specific benchmarks
-
-25:20.880 --> 25:23.920
- that don't generalize and full of magic numbers.
-
-25:23.920 --> 25:26.520
- And I hear there's some techniques
-
-25:26.520 --> 25:28.000
- that are good at handling that.
-
-25:28.000 --> 25:29.880
- So what would be the,
-
-25:29.880 --> 25:33.040
- if you were to apply machine learning to this,
-
-25:33.040 --> 25:34.720
- what's the thing you try to optimize?
-
-25:34.720 --> 25:38.080
- Is it ultimately the running time?
-
-25:38.080 --> 25:39.960
- Yeah, you can pick your metric
-
-25:39.960 --> 25:42.240
- and there's running time, there's memory use,
-
-25:42.240 --> 25:44.760
- there's lots of different things that you can optimize
-
-25:44.760 --> 25:47.200
- for code size is another one that some people care about
-
-25:47.200 --> 25:48.800
- in the embedded space.
-
-25:48.800 --> 25:51.680
- Is this like the thinking into the future
-
-25:51.680 --> 25:55.600
- or has somebody actually been crazy enough to try
-
-25:55.600 --> 25:59.080
- to have machine learning based parameter tuning
-
-25:59.080 --> 26:01.040
- for optimization of compilers?
-
-26:01.040 --> 26:04.840
- So this is something that is, I would say research right now.
-
-26:04.840 --> 26:06.800
- There are a lot of research systems
-
-26:06.800 --> 26:09.080
- that have been applying search in various forms
-
-26:09.080 --> 26:11.440
- and using reinforcement learning as one form,
-
-26:11.440 --> 26:14.400
- but also brute force search has been tried for quite a while.
-
-26:14.400 --> 26:18.160
- And usually these are in small problem spaces.
-
-26:18.160 --> 26:21.480
- So find the optimal way to code generate
-
-26:21.480 --> 26:23.680
- a matrix multiply for a GPU, right?
-
-26:23.680 --> 26:25.480
- Something like that where you say,
-
-26:25.480 --> 26:28.080
- there there's a lot of design space
-
-26:28.080 --> 26:29.920
- of do you unroll loops a lot?
-
-26:29.920 --> 26:32.600
- Do you execute multiple things in parallel?
-
-26:32.600 --> 26:35.320
- And there's many different confounding factors here
-
-26:35.320 --> 26:38.120
- because graphics cards have different numbers of threads
-
-26:38.120 --> 26:41.040
- and registers and execution ports and memory bandwidth
-
-26:41.040 --> 26:42.760
- and many different constraints to interact
-
-26:42.760 --> 26:44.280
- in nonlinear ways.
-
-26:44.280 --> 26:46.480
- And so search is very powerful for that
-
-26:46.480 --> 26:49.840
- and it gets used in certain ways,
-
-26:49.840 --> 26:51.240
- but it's not very structured.
-
-26:51.240 --> 26:52.640
- This is something that we need,
-
-26:52.640 --> 26:54.520
- we as an industry need to fix.
-
-26:54.520 --> 26:56.240
- So you said 80s, but like,
-
-26:56.240 --> 26:59.960
- so have there been like big jumps in improvement
-
-26:59.960 --> 27:01.280
- and optimization?
-
-27:01.280 --> 27:02.360
- Yeah.
-
-27:02.360 --> 27:05.320
- Yeah, since then, what's the coolest thing about it?
-
-27:05.320 --> 27:07.120
- It's largely been driven by hardware.
-
-27:07.120 --> 27:09.880
- So hardware and software.
-
-27:09.880 --> 27:13.880
- So in the mid 90s, Java totally changed the world, right?
-
-27:13.880 --> 27:17.520
- And I'm still amazed by how much change was introduced
-
-27:17.520 --> 27:19.320
- by Java in a good way or in a good way.
-
-27:19.320 --> 27:20.600
- So like reflecting back,
-
-27:20.600 --> 27:23.800
- Java introduced things like all at once introduced things
-
-27:23.800 --> 27:25.680
- like JIT compilation.
-
-27:25.680 --> 27:26.920
- None of these were novel,
-
-27:26.920 --> 27:28.640
- but it pulled it together and made it mainstream
-
-27:28.640 --> 27:30.600
- and made people invest in it.
-
-27:30.600 --> 27:32.680
- JIT compilation, garbage collection,
-
-27:32.680 --> 27:36.680
- portable code, safe code, like memory safe code,
-
-27:37.680 --> 27:41.480
- like a very dynamic dispatch execution model.
-
-27:41.480 --> 27:42.680
- Like many of these things,
-
-27:42.680 --> 27:44.120
- which had been done in research systems
-
-27:44.120 --> 27:46.960
- and had been done in small ways in various places,
-
-27:46.960 --> 27:48.040
- really came to the forefront
-
-27:48.040 --> 27:49.840
- and really changed how things worked.
-
-27:49.840 --> 27:52.040
- And therefore changed the way people thought
-
-27:52.040 --> 27:53.120
- about the problem.
-
-27:53.120 --> 27:56.360
- JavaScript was another major world change
-
-27:56.360 --> 27:57.780
- based on the way it works.
-
-27:59.320 --> 28:01.240
- But also on the hardware side of things,
-
-28:02.240 --> 28:05.200
- multi core and vector instructions
-
-28:05.200 --> 28:07.520
- really change the problem space
-
-28:07.520 --> 28:10.800
- and are very, they don't remove any of the problems
-
-28:10.800 --> 28:12.360
- that compilers faced in the past,
-
-28:12.360 --> 28:14.560
- but they add new kinds of problems
-
-28:14.560 --> 28:16.400
- of how do you find enough work
-
-28:16.400 --> 28:20.040
- to keep a four wide vector busy, right?
-
-28:20.040 --> 28:22.640
- Or if you're doing a matrix multiplication,
-
-28:22.640 --> 28:25.360
- how do you do different columns out of that matrix
-
-28:25.360 --> 28:26.680
- in at the same time?
-
-28:26.680 --> 28:30.160
- And how do you maximum utilize the arithmetic compute
-
-28:30.160 --> 28:31.440
- that one core has?
-
-28:31.440 --> 28:33.480
- And then how do you take it to multiple cores?
-
-28:33.480 --> 28:35.040
- How did the whole virtual machine thing
-
-28:35.040 --> 28:37.960
- change the compilation pipeline?
-
-28:37.960 --> 28:40.440
- Yeah, so what the Java virtual machine does
-
-28:40.440 --> 28:44.160
- is it splits, just like I was talking about before,
-
-28:44.160 --> 28:46.280
- where you have a front end that parses the code
-
-28:46.280 --> 28:47.960
- and then you have an intermediate representation
-
-28:47.960 --> 28:49.400
- that gets transformed.
-
-28:49.400 --> 28:50.960
- What Java did was they said,
-
-28:50.960 --> 28:52.720
- we will parse the code and then compile
-
-28:52.720 --> 28:55.480
- to what's known as Java bytecode.
-
-28:55.480 --> 28:58.560
- And that bytecode is now a portable code representation
-
-28:58.560 --> 29:02.400
- that is industry standard and locked down and can't change.
-
-29:02.400 --> 29:05.040
- And then the back part of the compiler
-
-29:05.040 --> 29:07.280
- that does optimization and code generation
-
-29:07.280 --> 29:09.440
- can now be built by different vendors.
-
-29:09.440 --> 29:12.080
- Okay, and Java bytecode can be shipped around
-
-29:12.080 --> 29:15.840
- across the wire, it's memory safe and relatively trusted.
-
-29:16.840 --> 29:18.680
- And because of that it can run in the browser.
-
-29:18.680 --> 29:20.480
- And that's why it runs in the browser, right?
-
-29:20.480 --> 29:22.960
- And so that way you can be in, you know,
-
-29:22.960 --> 29:25.000
- again, back in the day, you would write a Java applet
-
-29:25.000 --> 29:27.720
- and you'd use it as a web developer,
-
-29:27.720 --> 29:30.840
- you'd build this mini app that would run on a web page.
-
-29:30.840 --> 29:33.600
- Well, a user of that is running a web browser
-
-29:33.600 --> 29:36.160
- on their computer, you download that Java bytecode,
-
-29:36.160 --> 29:39.280
- which can be trusted, and then you do
-
-29:39.280 --> 29:41.040
- all the compiler stuff on your machine
-
-29:41.040 --> 29:42.400
- so that you know that you trust that.
-
-29:42.400 --> 29:44.080
- Is that a good idea or a bad idea?
-
-29:44.080 --> 29:44.920
- It's a great idea, I mean,
-
-29:44.920 --> 29:46.200
- it's a great idea for certain problems.
-
-29:46.200 --> 29:48.200
- And I'm very much a believer
-
-29:48.200 --> 29:50.480
- that the technology is itself neither good nor bad,
-
-29:50.480 --> 29:51.600
- it's how you apply it.
-
-29:52.920 --> 29:54.600
- You know, this would be a very, very bad thing
-
-29:54.600 --> 29:56.960
- for very low levels of the software stack,
-
-29:56.960 --> 30:00.280
- but in terms of solving some of these software portability
-
-30:00.280 --> 30:02.760
- and transparency or portability problems,
-
-30:02.760 --> 30:04.200
- I think it's been really good.
-
-30:04.200 --> 30:06.560
- Now Java ultimately didn't win out on the desktop
-
-30:06.560 --> 30:09.400
- and like there are good reasons for that,
-
-30:09.400 --> 30:13.200
- but it's been very successful on servers and in many places,
-
-30:13.200 --> 30:16.280
- it's been a very successful thing over decades.
-
-30:16.280 --> 30:21.280
- So what has been LLVM's and Selang's improvements
-
-30:24.480 --> 30:28.720
- and optimization that throughout its history,
-
-30:28.720 --> 30:31.080
- what are some moments we had set back
-
-30:31.080 --> 30:33.280
- and really proud of what's been accomplished?
-
-30:33.280 --> 30:36.200
- Yeah, I think that the interesting thing about LLVM
-
-30:36.200 --> 30:40.120
- is not the innovations in compiler research,
-
-30:40.120 --> 30:41.880
- it has very good implementations
-
-30:41.880 --> 30:43.880
- of very important algorithms, no doubt.
-
-30:43.880 --> 30:48.280
- And a lot of really smart people have worked on it,
-
-30:48.280 --> 30:50.560
- but I think that the thing that's most profound about LLVM
-
-30:50.560 --> 30:52.600
- is that through standardization,
-
-30:52.600 --> 30:55.720
- it made things possible that otherwise wouldn't have happened.
-
-30:55.720 --> 30:56.560
- Okay.
-
-30:56.560 --> 30:59.120
- And so interesting things that have happened with LLVM,
-
-30:59.120 --> 31:01.280
- for example, Sony has picked up LLVM
-
-31:01.280 --> 31:03.920
- and used it to do all the graphics compilation
-
-31:03.920 --> 31:06.080
- in their movie production pipeline.
-
-31:06.080 --> 31:07.920
- And so now they're able to have better special effects
-
-31:07.920 --> 31:09.680
- because of LLVM.
-
-31:09.680 --> 31:11.200
- That's kind of cool.
-
-31:11.200 --> 31:13.000
- That's not what it was designed for, right?
-
-31:13.000 --> 31:15.480
- But that's the sign of good infrastructure
-
-31:15.480 --> 31:18.800
- when it can be used in ways it was never designed for
-
-31:18.800 --> 31:20.960
- because it has good layering and software engineering
-
-31:20.960 --> 31:23.440
- and it's composable and things like that.
-
-31:23.440 --> 31:26.120
- Which is where, as you said, it differs from GCC.
-
-31:26.120 --> 31:28.240
- Yes, GCC is also great in various ways,
-
-31:28.240 --> 31:31.800
- but it's not as good as infrastructure technology.
-
-31:31.800 --> 31:36.120
- It's really a C compiler, or it's a 4 train compiler.
-
-31:36.120 --> 31:39.200
- It's not infrastructure in the same way.
-
-31:39.200 --> 31:40.400
- Is it, now you can tell,
-
-31:40.400 --> 31:41.560
- I don't know what I'm talking about
-
-31:41.560 --> 31:43.680
- because I keep saying C lang.
-
-31:44.520 --> 31:48.080
- You can always tell when a person is closed,
-
-31:48.080 --> 31:49.400
- by the way, pronounce something.
-
-31:49.400 --> 31:52.600
- I don't think, have I ever used Clang?
-
-31:52.600 --> 31:53.440
- Entirely possible.
-
-31:53.440 --> 31:55.680
- Have you, well, so you've used code,
-
-31:55.680 --> 31:58.200
- it's generated probably.
-
-31:58.200 --> 32:01.760
- So Clang is an LLVM or used to compile
-
-32:01.760 --> 32:05.240
- all the apps on the iPhone effectively and the OSes.
-
-32:05.240 --> 32:09.360
- It compiles Google's production server applications.
-
-32:09.360 --> 32:14.360
- It's used to build GameCube games and PlayStation 4
-
-32:14.880 --> 32:16.720
- and things like that.
-
-32:16.720 --> 32:17.920
- Those are the user I have,
-
-32:17.920 --> 32:20.800
- but just everything I've done that I experienced
-
-32:20.800 --> 32:23.600
- with Linux has been, I believe, always GCC.
-
-32:23.600 --> 32:25.720
- Yeah, I think Linux still defaults to GCC.
-
-32:25.720 --> 32:27.840
- And is there a reason for that?
-
-32:27.840 --> 32:29.480
- Or is it, I mean, is there a reason?
-
-32:29.480 --> 32:32.080
- It's a combination of technical and social reasons.
-
-32:32.080 --> 32:36.000
- Many Linux developers do use Clang,
-
-32:36.000 --> 32:40.600
- but the distributions, for lots of reasons,
-
-32:40.600 --> 32:44.280
- use GCC historically and they've not switched, yeah.
-
-32:44.280 --> 32:46.680
- Because it's just anecdotally online,
-
-32:46.680 --> 32:50.680
- it seems that LLVM has either reached the level of GCC
-
-32:50.680 --> 32:53.560
- or superseded on different features or whatever.
-
-32:53.560 --> 32:55.240
- The way I would say it is that they're so close
-
-32:55.240 --> 32:56.080
- it doesn't matter.
-
-32:56.080 --> 32:56.920
- Yeah, exactly.
-
-32:56.920 --> 32:58.160
- Like they're slightly better in some ways,
-
-32:58.160 --> 32:59.200
- slightly worse than otherwise,
-
-32:59.200 --> 33:03.320
- but it doesn't actually really matter anymore at that level.
-
-33:03.320 --> 33:06.320
- So in terms of optimization, breakthroughs,
-
-33:06.320 --> 33:09.200
- it's just been solid incremental work.
-
-33:09.200 --> 33:12.200
- Yeah, yeah, which describes a lot of compilers.
-
-33:12.200 --> 33:14.360
- The hard thing about compilers,
-
-33:14.360 --> 33:16.000
- in my experience, is the engineering,
-
-33:16.000 --> 33:18.680
- the software engineering, making it
-
-33:18.680 --> 33:20.920
- so that you can have hundreds of people collaborating
-
-33:20.920 --> 33:25.400
- on really detailed low level work and scaling that.
-
-33:25.400 --> 33:27.880
- And that's really hard.
-
-33:27.880 --> 33:30.720
- And that's one of the things I think LLVM has done well.
-
-33:30.720 --> 33:34.160
- And that kind of goes back to the original design goals
-
-33:34.160 --> 33:37.160
- with it to be modular and things like that.
-
-33:37.160 --> 33:38.840
- And incidentally, I don't want to take all the credit
-
-33:38.840 --> 33:39.680
- for this, right?
-
-33:39.680 --> 33:41.760
- I mean, some of the best parts about LLVM
-
-33:41.760 --> 33:43.600
- is that it was designed to be modular.
-
-33:43.600 --> 33:44.960
- And when I started, I would write,
-
-33:44.960 --> 33:46.840
- for example, a register allocator,
-
-33:46.840 --> 33:49.040
- and then somebody much smarter than me would come in
-
-33:49.040 --> 33:51.320
- and pull it out and replace it with something else
-
-33:51.320 --> 33:52.640
- that they would come up with.
-
-33:52.640 --> 33:55.160
- And because it's modular, they were able to do that.
-
-33:55.160 --> 33:58.240
- And that's one of the challenges with GCC, for example,
-
-33:58.240 --> 34:01.240
- is replacing subsystems is incredibly difficult.
-
-34:01.240 --> 34:04.640
- It can be done, but it wasn't designed for that.
-
-34:04.640 --> 34:06.040
- And that's one of the reasons that LLVM has been
-
-34:06.040 --> 34:08.720
- very successful in the research world as well.
-
-34:08.720 --> 34:11.040
- But in the community sense,
-
-34:11.040 --> 34:12.960
- Guido van Rasen, right?
-
-34:12.960 --> 34:16.880
- From Python, just retired from,
-
-34:18.080 --> 34:20.480
- what is it, benevolent, dictated for life, right?
-
-34:20.480 --> 34:24.720
- So in managing this community of brilliant compiler folks,
-
-34:24.720 --> 34:28.640
- is there, did it, for a time at least,
-
-34:28.640 --> 34:31.480
- fall on you to approve things?
-
-34:31.480 --> 34:34.240
- Oh yeah, so I mean, I still have something like
-
-34:34.240 --> 34:38.000
- an order of magnitude more patches in LLVM
-
-34:38.000 --> 34:39.000
- than anybody else.
-
-34:40.000 --> 34:42.760
- And many of those I wrote myself.
-
-34:42.760 --> 34:43.840
- But you're still right.
-
-34:43.840 --> 34:48.360
- I mean, you're still close to the,
-
-34:48.360 --> 34:50.040
- I don't know what the expression is to the metal.
-
-34:50.040 --> 34:51.040
- You're still right, Ko.
-
-34:51.040 --> 34:52.200
- Yeah, I'm still right, Ko.
-
-34:52.200 --> 34:54.240
- Not as much as I was able to in grad school,
-
-34:54.240 --> 34:56.760
- but that's an important part of my identity.
-
-34:56.760 --> 34:58.880
- But the way that LLVM has worked over time
-
-34:58.880 --> 35:00.440
- is that when I was a grad student,
-
-35:00.440 --> 35:03.000
- I could do all the work and steer everything
-
-35:03.000 --> 35:05.800
- and review every patch and make sure everything was done
-
-35:05.800 --> 35:09.040
- exactly the way my opinionated sense
-
-35:09.040 --> 35:10.640
- felt like it should be done.
-
-35:10.640 --> 35:11.760
- And that was fine.
-
-35:11.760 --> 35:14.320
- But as things scale, you can't do that, right?
-
-35:14.320 --> 35:18.040
- And so what ends up happening is LLVM has a hierarchical
-
-35:18.040 --> 35:20.520
- system of what's called code owners.
-
-35:20.520 --> 35:22.880
- These code owners are given the responsibility
-
-35:22.880 --> 35:24.920
- not to do all the work,
-
-35:24.920 --> 35:26.680
- not necessarily to review all the patches,
-
-35:26.680 --> 35:28.840
- but to make sure that the patches do get reviewed
-
-35:28.840 --> 35:30.360
- and make sure that the right thing's happening
-
-35:30.360 --> 35:32.200
- architecturally in their area.
-
-35:32.200 --> 35:34.200
- And so what you'll see is you'll see
-
-35:34.200 --> 35:37.760
- that for example, hardware manufacturers
-
-35:37.760 --> 35:40.920
- end up owning the hardware specific parts
-
-35:40.920 --> 35:44.520
- of their hardware, that's very common.
-
-35:45.560 --> 35:47.760
- Leaders in the community that have done really good work
-
-35:47.760 --> 35:50.920
- naturally become the de facto owner of something.
-
-35:50.920 --> 35:53.440
- And then usually somebody else is like,
-
-35:53.440 --> 35:55.520
- how about we make them the official code owner?
-
-35:55.520 --> 35:58.600
- And then we'll have somebody to make sure
-
-35:58.600 --> 36:00.320
- that all the patches get reviewed in a timely manner.
-
-36:00.320 --> 36:02.080
- And then everybody's like, yes, that's obvious.
-
-36:02.080 --> 36:03.240
- And then it happens, right?
-
-36:03.240 --> 36:06.080
- And usually this is a very organic thing, which is great.
-
-36:06.080 --> 36:08.720
- And so I'm nominally the top of that stack still,
-
-36:08.720 --> 36:11.560
- but I don't spend a lot of time reviewing patches.
-
-36:11.560 --> 36:16.520
- What I do is I help negotiate a lot of the technical
-
-36:16.520 --> 36:18.080
- disagreements that end up happening
-
-36:18.080 --> 36:19.680
- and making sure that the community as a whole
-
-36:19.680 --> 36:22.080
- makes progress and is moving in the right direction
-
-36:22.080 --> 36:23.960
- and doing that.
-
-36:23.960 --> 36:28.280
- So we also started a nonprofit six years ago,
-
-36:28.280 --> 36:30.880
- seven years ago, time's gone away.
-
-36:30.880 --> 36:34.640
- And the LVM Foundation nonprofit helps oversee
-
-36:34.640 --> 36:36.480
- all the business sides of things and make sure
-
-36:36.480 --> 36:39.680
- that the events that the LVM community has are funded
-
-36:39.680 --> 36:42.840
- and set up and run correctly and stuff like that.
-
-36:42.840 --> 36:45.200
- But the foundation is very much stays out
-
-36:45.200 --> 36:49.080
- of the technical side of where the project is going.
-
-36:49.080 --> 36:53.200
- Right, so it sounds like a lot of it is just organic, just.
-
-36:53.200 --> 36:55.720
- Yeah, well, and this is LVM is almost 20 years old,
-
-36:55.720 --> 36:56.640
- which is hard to believe.
-
-36:56.640 --> 37:00.360
- Somebody pointed out to me recently that LVM is now older
-
-37:00.360 --> 37:04.640
- than GCC was when LVM started, right?
-
-37:04.640 --> 37:06.880
- So time has a way of getting away from you.
-
-37:06.880 --> 37:10.440
- But the good thing about that is it has a really robust,
-
-37:10.440 --> 37:13.560
- really amazing community of people that are
-
-37:13.560 --> 37:14.720
- in their professional lives,
-
-37:14.720 --> 37:16.320
- spread across lots of different companies,
-
-37:16.320 --> 37:19.320
- but it's a community of people
-
-37:19.320 --> 37:21.160
- that are interested in similar kinds of problems
-
-37:21.160 --> 37:23.720
- and have been working together effectively for years
-
-37:23.720 --> 37:26.480
- and have a lot of trust and respect for each other.
-
-37:26.480 --> 37:28.960
- And even if they don't always agree that, you know,
-
-37:28.960 --> 37:31.200
- we're able to find a path forward.
-
-37:31.200 --> 37:34.520
- So then in a slightly different flavor of effort,
-
-37:34.520 --> 37:38.920
- you started at Apple in 2005 with the task of making,
-
-37:38.920 --> 37:41.840
- I guess, LVM production ready.
-
-37:41.840 --> 37:44.680
- And then eventually 2013 through 2017,
-
-37:44.680 --> 37:48.400
- leading the entire developer tools department.
-
-37:48.400 --> 37:53.000
- We're talking about LLVM, Xcode, Objective C to Swift.
-
-37:53.960 --> 37:58.600
- So in a quick overview of your time there,
-
-37:58.600 --> 37:59.640
- what were the challenges?
-
-37:59.640 --> 38:03.280
- First of all, leading such a huge group of developers.
-
-38:03.280 --> 38:06.560
- What was the big motivator dream mission
-
-38:06.560 --> 38:11.440
- behind creating Swift, the early birth of it
-
-38:11.440 --> 38:13.440
- from Objective C and so on and Xcode?
-
-38:13.440 --> 38:14.280
- What are some challenges?
-
-38:14.280 --> 38:15.920
- So these are different questions.
-
-38:15.920 --> 38:16.760
- Yeah, I know.
-
-38:16.760 --> 38:19.560
- But I want to talk about the other stuff too.
-
-38:19.560 --> 38:21.240
- I'll stay on the technical side,
-
-38:21.240 --> 38:23.440
- then we can talk about the big team pieces.
-
-38:23.440 --> 38:24.280
- That's okay?
-
-38:24.280 --> 38:25.120
- Sure.
-
-38:25.120 --> 38:27.760
- So it's to really oversimplify many years of hard work.
-
-38:27.760 --> 38:32.440
- LVM started, joined Apple, became a thing,
-
-38:32.440 --> 38:34.600
- became successful and became deployed.
-
-38:34.600 --> 38:36.760
- But then there was a question about
-
-38:36.760 --> 38:38.880
- how do we actually parse the source code?
-
-38:38.880 --> 38:40.320
- So LVM is that back part,
-
-38:40.320 --> 38:42.320
- the optimizer and the code generator.
-
-38:42.320 --> 38:44.640
- And LVM is really good for Apple as it went through
-
-38:44.640 --> 38:46.040
- a couple of hardware transitions.
-
-38:46.040 --> 38:47.920
- I joined right at the time of the Intel transition,
-
-38:47.920 --> 38:51.800
- for example, and 64 bit transitions
-
-38:51.800 --> 38:53.480
- and then the transition to ARM with the iPhone.
-
-38:53.480 --> 38:54.680
- And so LVM was very useful
-
-38:54.680 --> 38:56.920
- for some of these kinds of things.
-
-38:56.920 --> 38:57.760
- But at the same time,
-
-38:57.760 --> 39:00.080
- there's a lot of questions around developer experience.
-
-39:00.080 --> 39:01.880
- And so if you're a programmer pounding out
-
-39:01.880 --> 39:03.400
- at the time Objective C code,
-
-39:04.400 --> 39:06.440
- the error message you get, the compile time,
-
-39:06.440 --> 39:09.680
- the turnaround cycle, the tooling and the IDE
-
-39:09.680 --> 39:12.960
- were not great, were not as good as they could be.
-
-39:12.960 --> 39:17.960
- And so, as I occasionally do, I'm like,
-
-39:17.960 --> 39:20.080
- well, okay, how hard is it to write a C compiler?
-
-39:20.080 --> 39:20.920
- Right.
-
-39:20.920 --> 39:22.520
- And so I'm not gonna commit to anybody.
-
-39:22.520 --> 39:23.360
- I'm not gonna tell anybody.
-
-39:23.360 --> 39:25.960
- I'm just gonna just do it on nights and weekends
-
-39:25.960 --> 39:27.400
- and start working on it.
-
-39:27.400 --> 39:30.120
- And then I built up and see there's this thing
-
-39:30.120 --> 39:32.960
- called the preprocessor, which people don't like,
-
-39:32.960 --> 39:35.440
- but it's actually really hard and complicated
-
-39:35.440 --> 39:37.640
- and includes a bunch of really weird things
-
-39:37.640 --> 39:39.240
- like try graphs and other stuff like that
-
-39:39.240 --> 39:40.880
- that are really nasty.
-
-39:40.880 --> 39:44.000
- And it's the crux of a bunch of the performance issues
-
-39:44.000 --> 39:46.560
- in the compiler, start working on the parser
-
-39:46.560 --> 39:47.720
- and kind of got to the point where I'm like,
-
-39:47.720 --> 39:49.840
- oh, you know what, we could actually do this.
-
-39:49.840 --> 39:51.400
- Everybody's saying that this is impossible to do,
-
-39:51.400 --> 39:52.800
- but it's actually just hard.
-
-39:52.800 --> 39:53.880
- It's not impossible.
-
-39:53.880 --> 39:57.520
- And eventually told my manager about it
-
-39:57.520 --> 39:59.160
- and he's like, oh, wow, this is great.
-
-39:59.160 --> 40:00.280
- We do need to solve this problem.
-
-40:00.280 --> 40:01.120
- Oh, this is great.
-
-40:01.120 --> 40:04.360
- We can get you one other person to work with you on this.
-
-40:04.360 --> 40:08.240
- And so the team is formed and it starts taking off.
-
-40:08.240 --> 40:11.960
- And C++, for example, huge complicated language.
-
-40:11.960 --> 40:14.280
- People always assume that it's impossible to implement
-
-40:14.280 --> 40:16.160
- and it's very nearly impossible,
-
-40:16.160 --> 40:18.640
- but it's just really, really hard.
-
-40:18.640 --> 40:20.760
- And the way to get there is to build it
-
-40:20.760 --> 40:22.360
- one piece at a time incrementally.
-
-40:22.360 --> 40:26.360
- And that was only possible because we were lucky
-
-40:26.360 --> 40:28.080
- to hire some really exceptional engineers
-
-40:28.080 --> 40:30.280
- that knew various parts of it very well
-
-40:30.280 --> 40:32.600
- and could do great things.
-
-40:32.600 --> 40:34.360
- Swift was kind of a similar thing.
-
-40:34.360 --> 40:39.080
- So Swift came from, we were just finishing off
-
-40:39.080 --> 40:42.520
- the first version of C++ support in Clang.
-
-40:42.520 --> 40:47.160
- And C++ is a very formidable and very important language,
-
-40:47.160 --> 40:49.240
- but it's also ugly in lots of ways.
-
-40:49.240 --> 40:52.280
- And you can't implement C++ without thinking
-
-40:52.280 --> 40:54.320
- there has to be a better thing, right?
-
-40:54.320 --> 40:56.080
- And so I started working on Swift again
-
-40:56.080 --> 40:58.520
- with no hope or ambition that would go anywhere.
-
-40:58.520 --> 41:00.760
- Just let's see what could be done.
-
-41:00.760 --> 41:02.560
- Let's play around with this thing.
-
-41:02.560 --> 41:04.800
- It was me in my spare time,
-
-41:04.800 --> 41:08.160
- not telling anybody about it kind of a thing.
-
-41:08.160 --> 41:09.360
- And it made some good progress.
-
-41:09.360 --> 41:11.240
- I'm like, actually, it would make sense to do this.
-
-41:11.240 --> 41:14.760
- At the same time, I started talking with the senior VP
-
-41:14.760 --> 41:17.680
- of software at the time, a guy named Bertrand Sirle,
-
-41:17.680 --> 41:19.240
- and Bertrand was very encouraging.
-
-41:19.240 --> 41:22.040
- He was like, well, let's have fun, let's talk about this.
-
-41:22.040 --> 41:23.400
- And he was a little bit of a language guy.
-
-41:23.400 --> 41:26.120
- And so he helped guide some of the early work
-
-41:26.120 --> 41:30.360
- and encouraged me and got things off the ground.
-
-41:30.360 --> 41:34.240
- And eventually, I told my manager and told other people.
-
-41:34.240 --> 41:38.760
- And it started making progress.
-
-41:38.760 --> 41:40.920
- The complicating thing with Swift
-
-41:40.920 --> 41:43.840
- was that the idea of doing a new language
-
-41:43.840 --> 41:47.760
- is not obvious to anybody, including myself.
-
-41:47.760 --> 41:50.160
- And the tone at the time was that the iPhone
-
-41:50.160 --> 41:53.360
- was successful because of Objective C, right?
-
-41:53.360 --> 41:54.360
- Oh, interesting.
-
-41:54.360 --> 41:55.200
- In Objective C.
-
-41:55.200 --> 41:57.080
- Not despite of or just because of.
-
-41:57.080 --> 42:01.080
- And you have to understand that at the time,
-
-42:01.080 --> 42:05.360
- Apple was hiring software people that loved Objective C, right?
-
-42:05.360 --> 42:07.920
- And it wasn't that they came despite Objective C.
-
-42:07.920 --> 42:10.160
- They loved Objective C, and that's why they got hired.
-
-42:10.160 --> 42:13.680
- And so you had a software team that the leadership in many cases
-
-42:13.680 --> 42:18.440
- went all the way back to Next, where Objective C really became
-
-42:18.440 --> 42:19.320
- real.
-
-42:19.320 --> 42:23.200
- And so they, quote unquote, grew up writing Objective C.
-
-42:23.200 --> 42:25.680
- And many of the individual engineers
-
-42:25.680 --> 42:28.280
- all were hired because they loved Objective C.
-
-42:28.280 --> 42:30.520
- And so this notion of, OK, let's do new language
-
-42:30.520 --> 42:34.040
- was kind of heretical in many ways, right?
-
-42:34.040 --> 42:36.960
- Meanwhile, my sense was that the outside community wasn't really
-
-42:36.960 --> 42:38.520
- in love with Objective C. Some people were.
-
-42:38.520 --> 42:40.200
- And some of the most outspoken people were.
-
-42:40.200 --> 42:42.600
- But other people were hitting challenges
-
-42:42.600 --> 42:46.760
- because it has very sharp corners and it's difficult to learn.
-
-42:46.760 --> 42:50.040
- And so one of the challenges of making Swift happen
-
-42:50.040 --> 42:54.640
- that was totally non technical is the social part
-
-42:54.640 --> 42:57.760
- of what do we do?
-
-42:57.760 --> 43:00.280
- If we do a new language, which at Apple, many things
-
-43:00.280 --> 43:02.200
- happen that don't ship, right?
-
-43:02.200 --> 43:05.520
- So if we ship it, what is the metrics of success?
-
-43:05.520 --> 43:06.360
- Why would we do this?
-
-43:06.360 --> 43:07.920
- Why wouldn't we make Objective C better?
-
-43:07.920 --> 43:09.760
- If Objective C has problems, let's
-
-43:09.760 --> 43:12.120
- file off those rough corners and edges.
-
-43:12.120 --> 43:15.600
- And one of the major things that became the reason to do this
-
-43:15.600 --> 43:18.960
- was this notion of safety, memory safety.
-
-43:18.960 --> 43:22.880
- And the way Objective C works is that a lot of the object
-
-43:22.880 --> 43:26.440
- system and everything else is built on top of pointers
-
-43:26.440 --> 43:29.920
- in C. Objective C is an extension on top of C.
-
-43:29.920 --> 43:32.640
- And so pointers are unsafe.
-
-43:32.640 --> 43:34.600
- And if you get rid of the pointers,
-
-43:34.600 --> 43:36.400
- it's not Objective C anymore.
-
-43:36.400 --> 43:39.040
- And so fundamentally, that was an issue
-
-43:39.040 --> 43:42.160
- that you could not fix safety or memory safety
-
-43:42.160 --> 43:45.560
- without fundamentally changing the language.
-
-43:45.560 --> 43:49.880
- And so once we got through that part of the mental process
-
-43:49.880 --> 43:53.480
- and the thought process, it became a design process of saying,
-
-43:53.480 --> 43:56.240
- OK, well, if we're going to do something new, what is good?
-
-43:56.240 --> 43:57.400
- Like, how do we think about this?
-
-43:57.400 --> 43:59.960
- And what are we like, and what are we looking for?
-
-43:59.960 --> 44:02.400
- And that was a very different phase of it.
-
-44:02.400 --> 44:05.880
- So what are some design choices early on in Swift?
-
-44:05.880 --> 44:09.720
- Like, we're talking about braces.
-
-44:09.720 --> 44:12.040
- Are you making a type language or not?
-
-44:12.040 --> 44:13.200
- All those kinds of things.
-
-44:13.200 --> 44:16.000
- Yeah, so some of those were obvious given the context.
-
-44:16.000 --> 44:18.240
- So a type language, for example, Objective C
-
-44:18.240 --> 44:22.480
- is a type language, and going with an untyped language
-
-44:22.480 --> 44:24.280
- wasn't really seriously considered.
-
-44:24.280 --> 44:26.920
- We wanted the performance, and we wanted refactoring tools
-
-44:26.920 --> 44:29.600
- and other things like that that go with type languages.
-
-44:29.600 --> 44:30.800
- Quick dumb question.
-
-44:30.800 --> 44:31.400
- Yeah.
-
-44:31.400 --> 44:32.920
- Was it obvious?
-
-44:32.920 --> 44:34.600
- I think this would be a dumb question.
-
-44:34.600 --> 44:36.520
- But was it obvious that the language has
-
-44:36.520 --> 44:38.920
- to be a compiled language?
-
-44:38.920 --> 44:40.120
- Not an?
-
-44:40.120 --> 44:42.040
- Yes, that's not a dumb question.
-
-44:42.040 --> 44:44.000
- Earlier, I think late 90s, Apple
-
-44:44.000 --> 44:48.960
- had seriously considered moving its development experience to Java.
-
-44:48.960 --> 44:53.120
- But Swift started in 2010, which was several years
-
-44:53.120 --> 44:53.800
- after the iPhone.
-
-44:53.800 --> 44:56.600
- It was when the iPhone was definitely on an upper trajectory.
-
-44:56.600 --> 44:58.680
- And the iPhone was still extremely
-
-44:58.680 --> 45:01.760
- and is still a bit memory constrained.
-
-45:01.760 --> 45:05.480
- And so being able to compile the code and then ship it
-
-45:05.480 --> 45:09.720
- and then having standalone code that is not JIT compiled
-
-45:09.720 --> 45:11.320
- is a very big deal.
-
-45:11.320 --> 45:15.200
- And it's very much part of the Apple value system.
-
-45:15.200 --> 45:17.520
- Now, JavaScript's also a thing.
-
-45:17.520 --> 45:19.360
- I mean, it's not that this is exclusive,
-
-45:19.360 --> 45:23.880
- and technologies are good, depending on how they're applied.
-
-45:23.880 --> 45:27.200
- But in the design of Swift, saying how can we make
-
-45:27.200 --> 45:29.560
- Objective C better, Objective C was statically compiled,
-
-45:29.560 --> 45:32.480
- and that was the contiguous natural thing to do.
-
-45:32.480 --> 45:34.640
- Just skip ahead a little bit.
-
-45:34.640 --> 45:37.600
- Right back, just as a question, as you think about today
-
-45:37.600 --> 45:42.400
- in 2019, in your work at Google, TensorFlow, and so on,
-
-45:42.400 --> 45:47.480
- is, again, compilation, static compilation,
-
-45:47.480 --> 45:49.480
- still the right thing.
-
-45:49.480 --> 45:52.560
- Yeah, so the funny thing after working on compilers
-
-45:52.560 --> 45:56.480
- for a really long time is that, and this
-
-45:56.480 --> 45:59.080
- is one of the things that LLVM has helped with,
-
-45:59.080 --> 46:01.480
- is that I don't look at compilations
-
-46:01.480 --> 46:05.320
- being static or dynamic or interpreted or not.
-
-46:05.320 --> 46:09.160
- This is a spectrum, and one of the cool things about Swift
-
-46:09.160 --> 46:12.200
- is that Swift is not just statically compiled.
-
-46:12.200 --> 46:14.160
- It's actually dynamically compiled as well.
-
-46:14.160 --> 46:16.000
- And it can also be interpreted, though nobody's actually
-
-46:16.000 --> 46:17.560
- done that.
-
-46:17.560 --> 46:20.360
- And so what ends up happening when
-
-46:20.360 --> 46:22.760
- you use Swift in a workbook, for example,
-
-46:22.760 --> 46:25.320
- in Colab or in Jupyter, is it's actually dynamically
-
-46:25.320 --> 46:28.320
- compiling the statements as you execute them.
-
-46:28.320 --> 46:32.840
- And so this gets back to the software engineering problems,
-
-46:32.840 --> 46:34.960
- where if you layer the stack properly,
-
-46:34.960 --> 46:37.280
- you can actually completely change
-
-46:37.280 --> 46:39.320
- how and when things get compiled because you
-
-46:39.320 --> 46:41.120
- have the right abstractions there.
-
-46:41.120 --> 46:44.800
- And so the way that a Colab workbook works with Swift
-
-46:44.800 --> 46:47.720
- is that when you start typing into it,
-
-46:47.720 --> 46:50.320
- it creates a process, a UNIX process.
-
-46:50.320 --> 46:52.240
- And then each line of code you type in,
-
-46:52.240 --> 46:56.240
- it compiles it through the Swift compiler, the front end part,
-
-46:56.240 --> 46:58.400
- and then sends it through the optimizer,
-
-46:58.400 --> 47:01.120
- JIT compiles machine code, and then
-
-47:01.120 --> 47:03.920
- injects it into that process.
-
-47:03.920 --> 47:06.560
- And so as you're typing new stuff,
-
-47:06.560 --> 47:09.360
- it's like squirting in new code and overwriting and replacing
-
-47:09.360 --> 47:11.240
- and updating code in place.
-
-47:11.240 --> 47:13.520
- And the fact that it can do this is not an accident.
-
-47:13.520 --> 47:15.560
- Like Swift was designed for this.
-
-47:15.560 --> 47:18.120
- But it's an important part of how the language was set up
-
-47:18.120 --> 47:18.960
- and how it's layered.
-
-47:18.960 --> 47:21.360
- And this is a non obvious piece.
-
-47:21.360 --> 47:24.640
- And one of the things with Swift that was, for me,
-
-47:24.640 --> 47:27.040
- a very strong design point is to make it so that you
-
-47:27.040 --> 47:29.680
- can learn it very quickly.
-
-47:29.680 --> 47:32.080
- And so from a language design perspective,
-
-47:32.080 --> 47:34.520
- the thing that I always come back to is this UI principle
-
-47:34.520 --> 47:37.880
- of progressive disclosure of complexity.
-
-47:37.880 --> 47:41.680
- And so in Swift, you can start by saying print, quote,
-
-47:41.680 --> 47:43.960
- hello world, quote.
-
-47:43.960 --> 47:47.160
- And there's no slash n, just like Python, one line of code,
-
-47:47.160 --> 47:51.560
- no main, no header files, no public static class void,
-
-47:51.560 --> 47:55.600
- blah, blah, blah string, like Java has, one line of code.
-
-47:55.600 --> 47:58.280
- And you can teach that and it works great.
-
-47:58.280 --> 48:00.280
- Then you can say, well, let's introduce variables.
-
-48:00.280 --> 48:02.400
- And so you can declare a variable with var.
-
-48:02.400 --> 48:03.760
- So var x equals four.
-
-48:03.760 --> 48:04.680
- What is a variable?
-
-48:04.680 --> 48:06.280
- You can use x, x plus one.
-
-48:06.280 --> 48:07.720
- This is what it means.
-
-48:07.720 --> 48:09.480
- Then you can say, well, how about control flow?
-
-48:09.480 --> 48:10.840
- Well, this is one if statement is.
-
-48:10.840 --> 48:12.240
- This is what a for statement is.
-
-48:12.240 --> 48:15.320
- This is what a while statement is.
-
-48:15.320 --> 48:17.280
- Then you can say, let's introduce functions.
-
-48:17.280 --> 48:20.000
- And many languages like Python have
-
-48:20.000 --> 48:22.800
- had this kind of notion of let's introduce small things.
-
-48:22.800 --> 48:24.360
- And then you can add complexity.
-
-48:24.360 --> 48:25.720
- Then you can introduce classes.
-
-48:25.720 --> 48:28.040
- And then you can add generics in the case of Swift.
-
-48:28.040 --> 48:30.600
- And then you can build in modules and build out in terms
-
-48:30.600 --> 48:32.200
- of the things that you're expressing.
-
-48:32.200 --> 48:35.800
- But this is not very typical for compiled languages.
-
-48:35.800 --> 48:38.000
- And so this was a very strong design point.
-
-48:38.000 --> 48:40.960
- And one of the reasons that Swift in general
-
-48:40.960 --> 48:43.480
- is designed with this factoring of complexity in mind
-
-48:43.480 --> 48:46.440
- so that the language can express powerful things.
-
-48:46.440 --> 48:49.240
- You can write firmware in Swift if you want to.
-
-48:49.240 --> 48:52.800
- But it has a very high level feel, which is really
-
-48:52.800 --> 48:53.760
- this perfect blend.
-
-48:53.760 --> 48:57.440
- Because often you have very advanced library writers
-
-48:57.440 --> 49:00.520
- that want to be able to use the nitty gritty details.
-
-49:00.520 --> 49:02.960
- But then other people just want to use the libraries
-
-49:02.960 --> 49:04.880
- and work at a higher abstraction level.
-
-49:04.880 --> 49:07.200
- It's kind of cool that I saw that you can just
-
-49:07.200 --> 49:09.200
- enter a probability.
-
-49:09.200 --> 49:11.320
- I don't think I pronounced that word enough.
-
-49:11.320 --> 49:14.920
- But you can just drag in Python.
-
-49:14.920 --> 49:15.960
- It's just a string.
-
-49:15.960 --> 49:18.840
- You can import like, I saw this in the demo,
-
-49:18.840 --> 49:19.600
- import number.
-
-49:19.600 --> 49:20.760
- How do you make that happen?
-
-49:20.760 --> 49:21.240
- Yeah, well.
-
-49:21.240 --> 49:22.520
- What's up with that?
-
-49:22.520 --> 49:23.240
- Yeah.
-
-49:23.240 --> 49:24.960
- Is that as easy as it looks?
-
-49:24.960 --> 49:25.520
- Or is it?
-
-49:25.520 --> 49:26.560
- Yes, as easy as it looks.
-
-49:26.560 --> 49:29.440
- That's not a stage magic hack or anything like that.
-
-49:29.440 --> 49:31.400
- I don't mean from the user perspective.
-
-49:31.400 --> 49:33.200
- I mean from the implementation perspective
-
-49:33.200 --> 49:34.120
- to make it happen.
-
-49:34.120 --> 49:37.000
- So it's easy once all the pieces are in place.
-
-49:37.000 --> 49:37.920
- The way it works.
-
-49:37.920 --> 49:39.560
- So if you think about a dynamically typed language
-
-49:39.560 --> 49:42.160
- like Python, you can think about it in two different ways.
-
-49:42.160 --> 49:45.800
- You can say it has no types, which
-
-49:45.800 --> 49:47.480
- is what most people would say.
-
-49:47.480 --> 49:50.440
- Or you can say it has one type.
-
-49:50.440 --> 49:53.360
- And you can say it has one type and it's the Python object.
-
-49:53.360 --> 49:55.040
- And the Python object is passed around.
-
-49:55.040 --> 49:56.280
- And because there's only one type,
-
-49:56.280 --> 49:58.240
- it's implicit.
-
-49:58.240 --> 50:01.320
- And so what happens with Swift and Python talking to each other,
-
-50:01.320 --> 50:03.320
- Swift has lots of types, has arrays,
-
-50:03.320 --> 50:07.040
- and it has strings and all classes and that kind of stuff.
-
-50:07.040 --> 50:11.120
- But it now has a Python object type.
-
-50:11.120 --> 50:12.800
- So there is one Python object type.
-
-50:12.800 --> 50:16.440
- And so when you say import numpy, what you get
-
-50:16.440 --> 50:19.880
- is a Python object, which is the numpy module.
-
-50:19.880 --> 50:22.160
- And then you say np.array.
-
-50:22.160 --> 50:24.960
- It says, OK, hey Python object, I have no idea what you are.
-
-50:24.960 --> 50:27.280
- Give me your array member.
-
-50:27.280 --> 50:27.960
- OK, cool.
-
-50:27.960 --> 50:31.160
- And it just uses dynamic stuff, talks to the Python interpreter
-
-50:31.160 --> 50:33.680
- and says, hey Python, what's the dot array member
-
-50:33.680 --> 50:35.680
- in that Python object?
-
-50:35.680 --> 50:37.400
- It gives you back another Python object.
-
-50:37.400 --> 50:39.480
- And now you say, parentheses for the call
-
-50:39.480 --> 50:40.960
- and the arguments are going to pass.
-
-50:40.960 --> 50:43.640
- And so then it says, hey, a Python object that
-
-50:43.640 --> 50:48.040
- is the result of np.array, call with these arguments.
-
-50:48.040 --> 50:50.320
- Again, calling into the Python interpreter to do that work.
-
-50:50.320 --> 50:53.680
- And so right now, this is all really simple.
-
-50:53.680 --> 50:55.960
- And if you dive into the code, what you'll see
-
-50:55.960 --> 50:58.440
- is that the Python module in Swift
-
-50:58.440 --> 51:01.400
- is something like 1,200 lines of code or something.
-
-51:01.400 --> 51:02.360
- It's written in pure Swift.
-
-51:02.360 --> 51:03.560
- It's super simple.
-
-51:03.560 --> 51:06.560
- And it's built on top of the C interoperability
-
-51:06.560 --> 51:09.520
- because it just talks to the Python interpreter.
-
-51:09.520 --> 51:11.200
- But making that possible required us
-
-51:11.200 --> 51:13.480
- to add two major language features to Swift
-
-51:13.480 --> 51:15.400
- to be able to express these dynamic calls
-
-51:15.400 --> 51:17.200
- and the dynamic member lookups.
-
-51:17.200 --> 51:19.480
- And so what we've done over the last year
-
-51:19.480 --> 51:23.080
- is we've proposed, implement, standardized,
-
-51:23.080 --> 51:26.160
- and contributed new language features to the Swift language
-
-51:26.160 --> 51:29.560
- in order to make it so it is really trivial.
-
-51:29.560 --> 51:31.360
- And this is one of the things about Swift
-
-51:31.360 --> 51:35.000
- that is critical to the Swift for TensorFlow work, which
-
-51:35.000 --> 51:37.200
- is that we can actually add new language features.
-
-51:37.200 --> 51:39.160
- And the bar for adding those is high,
-
-51:39.160 --> 51:42.160
- but it's what makes it possible.
-
-51:42.160 --> 51:45.240
- So you're now at Google doing incredible work
-
-51:45.240 --> 51:47.680
- on several things, including TensorFlow.
-
-51:47.680 --> 51:52.240
- So TensorFlow 2.0 or whatever leading up to 2.0
-
-51:52.240 --> 51:57.360
- has, by default, in 2.0, has eager execution in yet
-
-51:57.360 --> 52:00.480
- in order to make code optimized for GPU or GPU
-
-52:00.480 --> 52:04.080
- or some of these systems computation
-
-52:04.080 --> 52:05.960
- needs to be converted to a graph.
-
-52:05.960 --> 52:07.400
- So what's that process like?
-
-52:07.400 --> 52:08.920
- What are the challenges there?
-
-52:08.920 --> 52:11.680
- Yeah, so I'm tangentially involved in this.
-
-52:11.680 --> 52:15.240
- But the way that it works with Autograph
-
-52:15.240 --> 52:21.600
- is that you mark your function with a decorator.
-
-52:21.600 --> 52:24.280
- And when Python calls it, that decorator is invoked.
-
-52:24.280 --> 52:28.240
- And then it says, before I call this function,
-
-52:28.240 --> 52:29.480
- you can transform it.
-
-52:29.480 --> 52:32.400
- And so the way Autograph works is, as far as I understand,
-
-52:32.400 --> 52:34.440
- is it actually uses the Python parser
-
-52:34.440 --> 52:37.160
- to go parse that, turn into a syntax tree,
-
-52:37.160 --> 52:39.400
- and now apply compiler techniques to, again,
-
-52:39.400 --> 52:42.320
- transform this down into TensorFlow graphs.
-
-52:42.320 --> 52:45.880
- And so you can think of it as saying, hey, I have an if statement.
-
-52:45.880 --> 52:48.800
- I'm going to create an if node in the graph, like you say,
-
-52:48.800 --> 52:51.080
- tf.cond.
-
-52:51.080 --> 52:53.000
- You have a multiply.
-
-52:53.000 --> 52:55.320
- Well, I'll turn that into a multiply node in the graph.
-
-52:55.320 --> 52:57.720
- And it becomes this tree transformation.
-
-52:57.720 --> 53:01.280
- So where does the Swift for TensorFlow come in?
-
-53:01.280 --> 53:04.720
- Which is parallels.
-
-53:04.720 --> 53:06.960
- For one, Swift is an interface.
-
-53:06.960 --> 53:09.200
- Like Python is an interface with TensorFlow.
-
-53:09.200 --> 53:11.200
- But it seems like there's a lot more going on
-
-53:11.200 --> 53:13.120
- than just a different language interface.
-
-53:13.120 --> 53:15.240
- There's optimization methodology.
-
-53:15.240 --> 53:19.560
- So the TensorFlow world has a couple of different, what
-
-53:19.560 --> 53:21.240
- I'd call front end technologies.
-
-53:21.240 --> 53:25.400
- And so Swift, and Python, and Go, and Rust, and Julian,
-
-53:25.400 --> 53:29.360
- all these things share the TensorFlow graphs
-
-53:29.360 --> 53:32.760
- and all the runtime and everything that's later.
-
-53:32.760 --> 53:36.680
- And so Swift for TensorFlow is merely another front end
-
-53:36.680 --> 53:40.680
- for TensorFlow, just like any of these other systems are.
-
-53:40.680 --> 53:43.120
- There's a major difference between, I would say,
-
-53:43.120 --> 53:44.640
- three camps of technologies here.
-
-53:44.640 --> 53:46.920
- There's Python, which is a special case,
-
-53:46.920 --> 53:49.280
- because the vast majority of the community efforts
-
-53:49.280 --> 53:51.160
- go into the Python interface.
-
-53:51.160 --> 53:53.000
- And Python has its own approaches
-
-53:53.000 --> 53:55.800
- for automatic differentiation, has its own APIs,
-
-53:55.800 --> 53:58.200
- and all this kind of stuff.
-
-53:58.200 --> 54:00.240
- There's Swift, which I'll talk about in a second.
-
-54:00.240 --> 54:02.080
- And then there's kind of everything else.
-
-54:02.080 --> 54:05.440
- And so the everything else are effectively language bindings.
-
-54:05.440 --> 54:08.000
- So they call into the TensorFlow runtime.
-
-54:08.000 --> 54:10.960
- But they usually don't have automatic differentiation,
-
-54:10.960 --> 54:14.760
- or they usually don't provide anything other than APIs that
-
-54:14.760 --> 54:16.480
- call the C APIs in TensorFlow.
-
-54:16.480 --> 54:18.400
- And so they're kind of wrappers for that.
-
-54:18.400 --> 54:19.840
- Swift is really kind of special.
-
-54:19.840 --> 54:22.800
- And it's a very different approach.
-
-54:22.800 --> 54:25.360
- Swift for TensorFlow, that is, is a very different approach,
-
-54:25.360 --> 54:26.920
- because there we're saying, let's
-
-54:26.920 --> 54:28.440
- look at all the problems that need
-
-54:28.440 --> 54:34.120
- to be solved in the full stack of the TensorFlow compilation
-
-54:34.120 --> 54:35.680
- process, if you think about it that way.
-
-54:35.680 --> 54:38.200
- Because TensorFlow is fundamentally a compiler.
-
-54:38.200 --> 54:42.760
- It takes models, and then it makes them go fast on hardware.
-
-54:42.760 --> 54:43.800
- That's what a compiler does.
-
-54:43.800 --> 54:47.560
- And it has a front end, it has an optimizer,
-
-54:47.560 --> 54:49.320
- and it has many back ends.
-
-54:49.320 --> 54:51.680
- And so if you think about it the right way,
-
-54:51.680 --> 54:54.760
- or if you look at it in a particular way,
-
-54:54.760 --> 54:55.800
- it is a compiler.
-
-54:59.280 --> 55:02.120
- And so Swift is merely another front end.
-
-55:02.120 --> 55:05.560
- But it's saying, and the design principle is saying,
-
-55:05.560 --> 55:08.200
- let's look at all the problems that we face as machine
-
-55:08.200 --> 55:11.200
- learning practitioners, and what is the best possible way
-
-55:11.200 --> 55:13.840
- we can do that, given the fact that we can change literally
-
-55:13.840 --> 55:15.920
- anything in this entire stack.
-
-55:15.920 --> 55:18.440
- And Python, for example, where the vast majority
-
-55:18.440 --> 55:22.600
- of the engineering and effort has gone into,
-
-55:22.600 --> 55:25.280
- is constrained by being the best possible thing you can do
-
-55:25.280 --> 55:27.280
- with a Python library.
-
-55:27.280 --> 55:29.280
- There are no Python language features
-
-55:29.280 --> 55:32.520
- that are added because of machine learning that I'm aware of.
-
-55:32.520 --> 55:35.080
- They added a matrix multiplication operator with that,
-
-55:35.080 --> 55:38.280
- but that's as close as you get.
-
-55:38.280 --> 55:41.400
- And so with Swift, it's hard, but you
-
-55:41.400 --> 55:43.800
- can add language features to the language,
-
-55:43.800 --> 55:46.080
- and there's a community process for that.
-
-55:46.080 --> 55:48.000
- And so we look at these things and say,
-
-55:48.000 --> 55:49.680
- well, what is the right division of labor
-
-55:49.680 --> 55:52.000
- between the human programmer and the compiler?
-
-55:52.000 --> 55:55.280
- And Swift has a number of things that shift that balance.
-
-55:55.280 --> 56:00.520
- So because it has a type system, for example,
-
-56:00.520 --> 56:03.280
- it makes certain things possible for analysis of the code,
-
-56:03.280 --> 56:05.520
- and the compiler can automatically
-
-56:05.520 --> 56:08.800
- build graphs for you without you thinking about them.
-
-56:08.800 --> 56:10.520
- That's a big deal for a programmer.
-
-56:10.520 --> 56:11.640
- You just get free performance.
-
-56:11.640 --> 56:14.360
- You get clustering and fusion and optimization,
-
-56:14.360 --> 56:17.440
- things like that, without you as a programmer having
-
-56:17.440 --> 56:20.040
- to manually do it because the compiler can do it for you.
-
-56:20.040 --> 56:22.200
- Automatic differentiation is another big deal,
-
-56:22.200 --> 56:25.440
- and I think one of the key contributions of the Swift
-
-56:25.440 --> 56:29.600
- for TensorFlow project is that there's
-
-56:29.600 --> 56:32.200
- this entire body of work on automatic differentiation that
-
-56:32.200 --> 56:34.240
- dates back to the Fortran days.
-
-56:34.240 --> 56:36.360
- People doing a tremendous amount of numerical computing
-
-56:36.360 --> 56:39.800
- in Fortran used to write what they call source to source
-
-56:39.800 --> 56:43.600
- translators, where you take a bunch of code, shove it
-
-56:43.600 --> 56:47.280
- into a mini compiler, and it would push out more Fortran
-
-56:47.280 --> 56:50.200
- code, but it would generate the backwards passes
-
-56:50.200 --> 56:53.000
- for your functions for you, the derivatives.
-
-56:53.000 --> 56:57.840
- And so in that work in the 70s, a tremendous number
-
-56:57.840 --> 57:01.160
- of optimizations, a tremendous number of techniques
-
-57:01.160 --> 57:02.920
- for fixing numerical instability,
-
-57:02.920 --> 57:05.080
- and other kinds of problems were developed,
-
-57:05.080 --> 57:07.600
- but they're very difficult to port into a world
-
-57:07.600 --> 57:11.280
- where in eager execution, you get an op by op at a time.
-
-57:11.280 --> 57:13.280
- Like, you need to be able to look at an entire function
-
-57:13.280 --> 57:15.600
- and be able to reason about what's going on.
-
-57:15.600 --> 57:18.360
- And so when you have a language integrated
-
-57:18.360 --> 57:20.480
- automatic differentiation, which is one of the things
-
-57:20.480 --> 57:22.760
- that the Swift project is focusing on,
-
-57:22.760 --> 57:25.720
- you can open all these techniques and reuse them
-
-57:25.720 --> 57:30.160
- in familiar ways, but the language integration piece
-
-57:30.160 --> 57:33.280
- has a bunch of design room in it, and it's also complicated.
-
-57:33.280 --> 57:34.920
- The other piece of the puzzle here,
-
-57:34.920 --> 57:37.040
- this kind of interesting is TPUs at Google.
-
-57:37.040 --> 57:37.880
- Yes.
-
-57:37.880 --> 57:40.200
- So, you know, we're in a new world with deep learning.
-
-57:40.200 --> 57:43.000
- It's constantly changing, and I imagine
-
-57:43.000 --> 57:46.400
- without disclosing anything, I imagine, you know,
-
-57:46.400 --> 57:48.480
- you're still innovating on the TPU front too.
-
-57:48.480 --> 57:49.320
- Indeed.
-
-57:49.320 --> 57:52.280
- So how much sort of interplays there are
-
-57:52.280 --> 57:54.440
- between software and hardware and trying to figure out
-
-57:54.440 --> 57:56.760
- how to gather, move towards an optimized solution.
-
-57:56.760 --> 57:57.800
- There's an incredible amount.
-
-57:57.800 --> 57:59.520
- So we're on our third generation of TPUs,
-
-57:59.520 --> 58:02.800
- which are now 100 petaflops in a very large
-
-58:02.800 --> 58:07.800
- liquid cooled box, virtual box with no cover.
-
-58:07.800 --> 58:11.320
- And as you might imagine, we're not out of ideas yet.
-
-58:11.320 --> 58:14.400
- The great thing about TPUs is that they're
-
-58:14.400 --> 58:17.640
- a perfect example of hardware software co design.
-
-58:17.640 --> 58:19.840
- And so it's about saying, what hardware
-
-58:19.840 --> 58:23.280
- do we build to solve certain classes of machine learning
-
-58:23.280 --> 58:23.920
- problems?
-
-58:23.920 --> 58:26.360
- Well, the algorithms are changing.
-
-58:26.360 --> 58:30.480
- Like the hardware takes some cases years to produce, right?
-
-58:30.480 --> 58:34.160
- And so you have to make bets and decide what is going to happen.
-
-58:34.160 --> 58:37.280
- And so what is the best way to spend the transistors
-
-58:37.280 --> 58:41.560
- to get the maximum performance per watt or area per cost
-
-58:41.560 --> 58:44.120
- or whatever it is that you're optimizing for?
-
-58:44.120 --> 58:46.600
- And so one of the amazing things about TPUs
-
-58:46.600 --> 58:50.040
- is this numeric format called B Float 16.
-
-58:50.040 --> 58:54.160
- B Float 16 is a compressed 16 bit floating point format,
-
-58:54.160 --> 58:56.120
- but it puts the bits in different places.
-
-58:56.120 --> 58:59.000
- In numeric terms, it has a smaller mantissa
-
-58:59.000 --> 59:00.480
- and a larger exponent.
-
-59:00.480 --> 59:03.000
- That means that it's less precise,
-
-59:03.000 --> 59:06.120
- but it can represent larger ranges of values, which
-
-59:06.120 --> 59:08.640
- in the machine learning context is really important and useful.
-
-59:08.640 --> 59:13.120
- Because sometimes you have very small gradients
-
-59:13.120 --> 59:17.600
- you want to accumulate and very, very small numbers that
-
-59:17.600 --> 59:20.520
- are important to move things as you're learning.
-
-59:20.520 --> 59:23.240
- But sometimes you have very large magnitude numbers as well.
-
-59:23.240 --> 59:26.880
- And B Float 16 is not as precise.
-
-59:26.880 --> 59:28.240
- The mantissa is small.
-
-59:28.240 --> 59:30.360
- But it turns out the machine learning algorithms actually
-
-59:30.360 --> 59:31.640
- want to generalize.
-
-59:31.640 --> 59:34.320
- And so there's theories that this actually
-
-59:34.320 --> 59:36.440
- increases the ability for the network
-
-59:36.440 --> 59:38.040
- to generalize across data sets.
-
-59:38.040 --> 59:41.160
- And regardless of whether it's good or bad,
-
-59:41.160 --> 59:42.640
- it's much cheaper at the hardware level
-
-59:42.640 --> 59:48.160
- to implement because the area and time of a multiplier
-
-59:48.160 --> 59:50.880
- is n squared in the number of bits in the mantissa,
-
-59:50.880 --> 59:53.360
- but it's linear with size of the exponent.
-
-59:53.360 --> 59:56.360
- And you're connected to both efforts here, both on the hardware
-
-59:56.360 --> 59:57.200
- and the software side?
-
-59:57.200 --> 59:59.240
- Yeah, and so that was a breakthrough coming
-
-59:59.240 --> 1:00:01.800
- from the research side and people working
-
-1:00:01.800 --> 1:00:06.000
- on optimizing network transport of weights
-
-1:00:06.000 --> 1:00:08.280
- across a network originally and trying
-
-1:00:08.280 --> 1:00:10.160
- to find ways to compress that.
-
-1:00:10.160 --> 1:00:12.160
- But then it got burned into silicon.
-
-1:00:12.160 --> 1:00:15.320
- And it's a key part of what makes TPU performance so amazing.
-
-1:00:15.320 --> 1:00:17.880
- And great.
-
-1:00:17.880 --> 1:00:20.640
- Now, TPUs have many different aspects that are important.
-
-1:00:20.640 --> 1:00:25.080
- But the co design between the low level compiler bits
-
-1:00:25.080 --> 1:00:27.360
- and the software bits and the algorithms
-
-1:00:27.360 --> 1:00:28.640
- is all super important.
-
-1:00:28.640 --> 1:00:32.880
- And it's this amazing trifecta that only Google can do.
-
-1:00:32.880 --> 1:00:34.360
- Yeah, that's super exciting.
-
-1:00:34.360 --> 1:00:38.440
- So can you tell me about MLIR project,
-
-1:00:38.440 --> 1:00:41.400
- previously the secretive one?
-
-1:00:41.400 --> 1:00:43.000
- Yeah, so MLIR is a project that we
-
-1:00:43.000 --> 1:00:46.960
- announced at a compiler conference three weeks ago
-
-1:00:46.960 --> 1:00:50.880
- or something at the Compilers for Machine Learning Conference.
-
-1:00:50.880 --> 1:00:53.280
- Basically, again, if you look at TensorFlow as a compiler
-
-1:00:53.280 --> 1:00:55.040
- stack, it has a number of compiler algorithms
-
-1:00:55.040 --> 1:00:56.000
- within it.
-
-1:00:56.000 --> 1:00:57.480
- It also has a number of compilers
-
-1:00:57.480 --> 1:00:58.880
- that get embedded into it.
-
-1:00:58.880 --> 1:01:00.320
- And they're made by different vendors.
-
-1:01:00.320 --> 1:01:04.640
- For example, Google has XLA, which is a great compiler system.
-
-1:01:04.640 --> 1:01:08.680
- NVIDIA has TensorFlow RT, Intel has NGraph.
-
-1:01:08.680 --> 1:01:10.640
- There's a number of these different compiler systems.
-
-1:01:10.640 --> 1:01:13.600
- And they're very hardware specific.
-
-1:01:13.600 --> 1:01:16.280
- And they're trying to solve different parts of the problems.
-
-1:01:16.280 --> 1:01:18.920
- But they're all kind of similar in a sense
-
-1:01:18.920 --> 1:01:20.680
- of they want to integrate with TensorFlow.
-
-1:01:20.680 --> 1:01:22.720
- Now, TensorFlow has an optimizer.
-
-1:01:22.720 --> 1:01:25.480
- And it has these different code generation technologies
-
-1:01:25.480 --> 1:01:26.360
- built in.
-
-1:01:26.360 --> 1:01:28.680
- The idea of MLIR is to build a common infrastructure
-
-1:01:28.680 --> 1:01:31.040
- to support all these different subsystems.
-
-1:01:31.040 --> 1:01:34.120
- And initially, it's to be able to make it so that they all
-
-1:01:34.120 --> 1:01:34.840
- plug in together.
-
-1:01:34.840 --> 1:01:37.800
- And they can share a lot more code and can be reusable.
-
-1:01:37.800 --> 1:01:40.960
- But over time, we hope that the industry will start
-
-1:01:40.960 --> 1:01:42.440
- collaborating and sharing code.
-
-1:01:42.440 --> 1:01:45.200
- And instead of reinventing the same things over and over again,
-
-1:01:45.200 --> 1:01:49.240
- that we can actually foster some of that working together
-
-1:01:49.240 --> 1:01:51.520
- to solve common problem energy that
-
-1:01:51.520 --> 1:01:54.440
- has been useful in the compiler field before.
-
-1:01:54.440 --> 1:01:57.000
- Beyond that, MLIR is some people have
-
-1:01:57.000 --> 1:01:59.240
- joked that it's kind of LLVM2.
-
-1:01:59.240 --> 1:02:01.760
- It learns a lot about what LLVM has been good
-
-1:02:01.760 --> 1:02:04.280
- and what LLVM has done wrong.
-
-1:02:04.280 --> 1:02:06.800
- And it's a chance to fix that.
-
-1:02:06.800 --> 1:02:09.320
- And also, there are challenges in the LLVM ecosystem
-
-1:02:09.320 --> 1:02:11.840
- as well, where LLVM is very good at the thing
-
-1:02:11.840 --> 1:02:12.680
- it was designed to do.
-
-1:02:12.680 --> 1:02:15.480
- But 20 years later, the world has changed.
-
-1:02:15.480 --> 1:02:17.560
- And people are trying to solve higher level problems.
-
-1:02:17.560 --> 1:02:20.280
- And we need some new technology.
-
-1:02:20.280 --> 1:02:24.680
- And what's the future of open source in this context?
-
-1:02:24.680 --> 1:02:25.680
- Very soon.
-
-1:02:25.680 --> 1:02:27.440
- So it is not yet open source.
-
-1:02:27.440 --> 1:02:29.360
- But it will be, hopefully, the next couple of months.
-
-1:02:29.360 --> 1:02:30.960
- So you still believe in the value of open source
-
-1:02:30.960 --> 1:02:31.560
- and these kinds of kinds?
-
-1:02:31.560 --> 1:02:32.400
- Oh, yeah, absolutely.
-
-1:02:32.400 --> 1:02:36.080
- And I think that the TensorFlow community at large
-
-1:02:36.080 --> 1:02:37.640
- fully believes in open source.
-
-1:02:37.640 --> 1:02:40.080
- So I mean, there is a difference between Apple,
-
-1:02:40.080 --> 1:02:43.480
- where you were previously in Google, now in spirit and culture.
-
-1:02:43.480 --> 1:02:45.440
- And I would say the open sourcing of TensorFlow
-
-1:02:45.440 --> 1:02:48.360
- was a seminal moment in the history of software.
-
-1:02:48.360 --> 1:02:51.640
- Because here's this large company releasing
-
-1:02:51.640 --> 1:02:55.880
- a very large code base that's open sourcing.
-
-1:02:55.880 --> 1:02:57.880
- What are your thoughts on that?
-
-1:02:57.880 --> 1:03:00.800
- How happy or not were you to see that kind
-
-1:03:00.800 --> 1:03:02.880
- of degree of open sourcing?
-
-1:03:02.880 --> 1:03:05.320
- So between the two, I prefer the Google approach,
-
-1:03:05.320 --> 1:03:07.800
- if that's what you're saying.
-
-1:03:07.800 --> 1:03:12.360
- The Apple approach makes sense given the historical context
-
-1:03:12.360 --> 1:03:13.360
- that Apple came from.
-
-1:03:13.360 --> 1:03:15.720
- But that's been 35 years ago.
-
-1:03:15.720 --> 1:03:18.160
- And I think that Apple is definitely adapting.
-
-1:03:18.160 --> 1:03:20.240
- And the way I look at it is that there's
-
-1:03:20.240 --> 1:03:23.120
- different kinds of concerns in the space, right?
-
-1:03:23.120 --> 1:03:24.840
- It is very rational for a business
-
-1:03:24.840 --> 1:03:28.680
- to care about making money.
-
-1:03:28.680 --> 1:03:31.600
- That fundamentally is what a business is about, right?
-
-1:03:31.600 --> 1:03:34.280
- But I think it's also incredibly realistic
-
-1:03:34.280 --> 1:03:36.320
- to say it's not your string library that's
-
-1:03:36.320 --> 1:03:38.040
- the thing that's going to make you money.
-
-1:03:38.040 --> 1:03:41.440
- It's going to be the amazing UI product differentiating
-
-1:03:41.440 --> 1:03:42.880
- features and other things like that
-
-1:03:42.880 --> 1:03:45.200
- that you build on top of your string library.
-
-1:03:45.200 --> 1:03:49.480
- And so keeping your string library proprietary and secret
-
-1:03:49.480 --> 1:03:53.480
- and things like that isn't maybe not the important thing
-
-1:03:53.480 --> 1:03:54.680
- anymore, right?
-
-1:03:54.680 --> 1:03:57.720
- Or before, platforms were different, right?
-
-1:03:57.720 --> 1:04:01.480
- And even 15 years ago, things were a little bit different.
-
-1:04:01.480 --> 1:04:02.880
- But the world is changing.
-
-1:04:02.880 --> 1:04:05.280
- So Google strikes a very good balance, I think.
-
-1:04:05.280 --> 1:04:08.680
- And I think that TensorFlow being open source
-
-1:04:08.680 --> 1:04:12.000
- really changed the entire machine learning field
-
-1:04:12.000 --> 1:04:14.080
- and it caused a revolution in its own right.
-
-1:04:14.080 --> 1:04:17.560
- And so I think it's amazingly forward looking
-
-1:04:17.560 --> 1:04:21.520
- because I could have imagined, and I wasn't at Google at the time,
-
-1:04:21.520 --> 1:04:23.760
- but I could imagine a different context in a different world
-
-1:04:23.760 --> 1:04:26.520
- where a company says, machine learning is critical
-
-1:04:26.520 --> 1:04:27.960
- to what we're doing, we're not going
-
-1:04:27.960 --> 1:04:29.600
- to give it to other people, right?
-
-1:04:29.600 --> 1:04:35.840
- And so that decision is a profoundly brilliant insight
-
-1:04:35.840 --> 1:04:38.320
- that I think has really led to the world being better
-
-1:04:38.320 --> 1:04:40.160
- and better for Google as well.
-
-1:04:40.160 --> 1:04:42.200
- And has all kinds of ripple effects.
-
-1:04:42.200 --> 1:04:45.400
- I think it is really, I mean, you can't
-
-1:04:45.400 --> 1:04:49.800
- understate Google deciding how profound that is for software.
-
-1:04:49.800 --> 1:04:50.840
- It's awesome.
-
-1:04:50.840 --> 1:04:54.880
- Well, and again, I can understand the concern
-
-1:04:54.880 --> 1:04:57.640
- about if we release our machine learning software,
-
-1:04:57.640 --> 1:05:00.400
- our competitors could go faster.
-
-1:05:00.400 --> 1:05:02.480
- But on the other hand, I think that open sourcing TensorFlow
-
-1:05:02.480 --> 1:05:03.960
- has been fantastic for Google.
-
-1:05:03.960 --> 1:05:09.080
- And I'm sure that decision was very nonobvious at the time,
-
-1:05:09.080 --> 1:05:11.480
- but I think it's worked out very well.
-
-1:05:11.480 --> 1:05:13.200
- So let's try this real quick.
-
-1:05:13.200 --> 1:05:15.600
- You were at Tesla for five months
-
-1:05:15.600 --> 1:05:17.600
- as the VP of autopilot software.
-
-1:05:17.600 --> 1:05:20.480
- You led the team during the transition from H Hardware
-
-1:05:20.480 --> 1:05:22.320
- 1 to Hardware 2.
-
-1:05:22.320 --> 1:05:23.480
- I have a couple of questions.
-
-1:05:23.480 --> 1:05:26.320
- So one, first of all, to me, that's
-
-1:05:26.320 --> 1:05:28.520
- one of the bravest engineering decisions
-
-1:05:28.520 --> 1:05:33.320
- undertaking sort of like, undertaking really ever
-
-1:05:33.320 --> 1:05:36.000
- in the automotive industry to me, software wise,
-
-1:05:36.000 --> 1:05:37.440
- starting from scratch.
-
-1:05:37.440 --> 1:05:39.320
- It's a really brave engineering decision.
-
-1:05:39.320 --> 1:05:42.760
- So my one question is there is, what was that like?
-
-1:05:42.760 --> 1:05:43.960
- What was the challenge of that?
-
-1:05:43.960 --> 1:05:45.760
- Do you mean the career decision of jumping
-
-1:05:45.760 --> 1:05:48.880
- from a comfortable good job into the unknown?
-
-1:05:48.880 --> 1:05:51.560
- That combined, so at the individual level,
-
-1:05:51.560 --> 1:05:54.640
- you making that decision.
-
-1:05:54.640 --> 1:05:58.040
- And then when you show up, it's a really hard engineering
-
-1:05:58.040 --> 1:05:58.840
- problem.
-
-1:05:58.840 --> 1:06:04.880
- So you could just stay, maybe slow down, say, Hardware 1,
-
-1:06:04.880 --> 1:06:06.560
- or those kinds of decisions.
-
-1:06:06.560 --> 1:06:10.160
- So just taking it full on, let's do this from scratch.
-
-1:06:10.160 --> 1:06:11.080
- What was that like?
-
-1:06:11.080 --> 1:06:12.680
- Well, so I mean, I don't think Tesla
-
-1:06:12.680 --> 1:06:15.720
- has a culture of taking things slow and seeing how it goes.
-
-1:06:15.720 --> 1:06:18.080
- So one of the things that attracted me about Tesla
-
-1:06:18.080 --> 1:06:19.240
- is it's very much a gung ho.
-
-1:06:19.240 --> 1:06:20.200
- Let's change the world.
-
-1:06:20.200 --> 1:06:21.640
- Let's figure it out kind of a place.
-
-1:06:21.640 --> 1:06:25.680
- And so I have a huge amount of respect for that.
-
-1:06:25.680 --> 1:06:28.720
- Tesla has done very smart things with Hardware 1
-
-1:06:28.720 --> 1:06:29.440
- in particular.
-
-1:06:29.440 --> 1:06:32.760
- And the Hardware 1 design was originally designed
-
-1:06:32.760 --> 1:06:37.280
- to be very simple automation features in the car
-
-1:06:37.280 --> 1:06:39.840
- for like traffic aware cruise control and things like that.
-
-1:06:39.840 --> 1:06:42.680
- And the fact that they were able to effectively feature
-
-1:06:42.680 --> 1:06:47.760
- creep it into lane holding and a very useful driver assistance
-
-1:06:47.760 --> 1:06:50.120
- feature is pretty astounding, particularly given
-
-1:06:50.120 --> 1:06:52.560
- the details of the hardware.
-
-1:06:52.560 --> 1:06:54.640
- Hardware 2 built on that in a lot of ways.
-
-1:06:54.640 --> 1:06:56.800
- And the challenge there was that they were transitioning
-
-1:06:56.800 --> 1:07:00.080
- from a third party provided vision stack
-
-1:07:00.080 --> 1:07:01.760
- to an in house built vision stack.
-
-1:07:01.760 --> 1:07:05.680
- And so for the first step, which I mostly helped with,
-
-1:07:05.680 --> 1:07:08.520
- was getting onto that new vision stack.
-
-1:07:08.520 --> 1:07:10.880
- And that was very challenging.
-
-1:07:10.880 --> 1:07:14.000
- And it was time critical for various reasons.
-
-1:07:14.000 --> 1:07:15.000
- And it was a big leap.
-
-1:07:15.000 --> 1:07:17.560
- But it was fortunate that it built on a lot of the knowledge
-
-1:07:17.560 --> 1:07:20.880
- and expertise in the team that had built Hardware 1's
-
-1:07:20.880 --> 1:07:22.920
- driver assistance features.
-
-1:07:22.920 --> 1:07:25.400
- So you spoke in a collected and kind way
-
-1:07:25.400 --> 1:07:26.720
- about your time at Tesla.
-
-1:07:26.720 --> 1:07:30.280
- But it was ultimately not a good fit Elon Musk.
-
-1:07:30.280 --> 1:07:33.440
- We've talked on this podcast, several guests of the course.
-
-1:07:33.440 --> 1:07:36.480
- Elon Musk continues to do some of the most bold and innovative
-
-1:07:36.480 --> 1:07:38.800
- engineering work in the world at times
-
-1:07:38.800 --> 1:07:41.320
- at the cost to some of the members of the Tesla team.
-
-1:07:41.320 --> 1:07:45.120
- What did you learn about this working in this chaotic world
-
-1:07:45.120 --> 1:07:46.720
- with Elon?
-
-1:07:46.720 --> 1:07:50.560
- Yeah, so I guess I would say that when I was at Tesla,
-
-1:07:50.560 --> 1:07:54.480
- I experienced and saw the highest degree of turnover
-
-1:07:54.480 --> 1:07:58.280
- I'd ever seen in a company, which was a bit of a shock.
-
-1:07:58.280 --> 1:08:00.520
- But one of the things I learned and I came to respect
-
-1:08:00.520 --> 1:08:03.400
- is that Elon's able to attract amazing talent
-
-1:08:03.400 --> 1:08:05.640
- because he has a very clear vision of the future.
-
-1:08:05.640 --> 1:08:07.200
- And he can get people to buy into it
-
-1:08:07.200 --> 1:08:09.840
- because they want that future to happen.
-
-1:08:09.840 --> 1:08:11.840
- And the power of vision is something
-
-1:08:11.840 --> 1:08:14.200
- that I have a tremendous amount of respect for.
-
-1:08:14.200 --> 1:08:17.600
- And I think that Elon is fairly singular in the world
-
-1:08:17.600 --> 1:08:22.320
- in terms of the things he's able to get people to believe in.
-
-1:08:22.320 --> 1:08:27.360
- And there are many people that stand in the street corner
-
-1:08:27.360 --> 1:08:29.320
- and say, ah, we're going to go to Mars, right?
-
-1:08:29.320 --> 1:08:31.600
- But then there are a few people that
-
-1:08:31.600 --> 1:08:35.200
- can get others to buy into it and believe in, build the path
-
-1:08:35.200 --> 1:08:36.160
- and make it happen.
-
-1:08:36.160 --> 1:08:39.120
- And so I respect that.
-
-1:08:39.120 --> 1:08:41.000
- I don't respect all of his methods,
-
-1:08:41.000 --> 1:08:44.960
- but I have a huge amount of respect for that.
-
-1:08:44.960 --> 1:08:46.840
- You've mentioned in a few places,
-
-1:08:46.840 --> 1:08:50.400
- including in this context, working hard.
-
-1:08:50.400 --> 1:08:51.960
- What does it mean to work hard?
-
-1:08:51.960 --> 1:08:53.480
- And when you look back at your life,
-
-1:08:53.480 --> 1:08:59.040
- what were some of the most brutal periods of having
-
-1:08:59.040 --> 1:09:03.360
- to really put everything you have into something?
-
-1:09:03.360 --> 1:09:05.040
- Yeah, good question.
-
-1:09:05.040 --> 1:09:07.480
- So working hard can be defined a lot of different ways.
-
-1:09:07.480 --> 1:09:08.680
- So a lot of hours.
-
-1:09:08.680 --> 1:09:12.440
- And so that is true.
-
-1:09:12.440 --> 1:09:14.480
- The thing to me that's the hardest
-
-1:09:14.480 --> 1:09:18.720
- is both being short term focused on delivering and executing
-
-1:09:18.720 --> 1:09:21.080
- and making a thing happen, while also thinking
-
-1:09:21.080 --> 1:09:24.360
- about the longer term and trying to balance that, right?
-
-1:09:24.360 --> 1:09:28.480
- Because if you are myopically focused on solving a task
-
-1:09:28.480 --> 1:09:31.920
- and getting that done and only think about that incremental
-
-1:09:31.920 --> 1:09:34.640
- next step, you will miss the next big hill
-
-1:09:34.640 --> 1:09:36.360
- you should jump over to, right?
-
-1:09:36.360 --> 1:09:38.000
- And so I've been really fortunate
-
-1:09:38.000 --> 1:09:42.080
- that I've been able to kind of oscillate between the two.
-
-1:09:42.080 --> 1:09:45.600
- And historically at Apple, for example,
-
-1:09:45.600 --> 1:09:47.080
- that was made possible because I was
-
-1:09:47.080 --> 1:09:49.080
- able to work with some really amazing people and build up
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-1:09:49.080 --> 1:09:53.760
- teams and leadership structures and allow
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-1:09:53.760 --> 1:09:57.120
- them to grow in their careers and take on responsibility,
-
-1:09:57.120 --> 1:10:00.080
- thereby freeing up me to be a little bit crazy
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-1:10:00.080 --> 1:10:02.960
- and thinking about the next thing.
-
-1:10:02.960 --> 1:10:04.640
- And so it's a lot of that.
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-1:10:04.640 --> 1:10:06.760
- But it's also about with the experience
-
-1:10:06.760 --> 1:10:10.120
- you make connections that other people don't necessarily make.
-
-1:10:10.120 --> 1:10:12.960
- And so I think that's a big part as well.
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-1:10:12.960 --> 1:10:16.040
- But the bedrock is just a lot of hours.
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-1:10:16.040 --> 1:10:19.720
- And that's OK with me.
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-1:10:19.720 --> 1:10:21.480
- There's different theories on work life balance.
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-1:10:21.480 --> 1:10:25.160
- And my theory for myself, which I do not project onto the team,
-
-1:10:25.160 --> 1:10:28.480
- but my theory for myself is that I
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-1:10:28.480 --> 1:10:30.400
- want to love what I'm doing and work really hard.
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-1:10:30.400 --> 1:10:33.960
- And my purpose, I feel like, and my goal
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-1:10:33.960 --> 1:10:36.240
- is to change the world and make it a better place.
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-1:10:36.240 --> 1:10:40.000
- And that's what I'm really motivated to do.
-
-1:10:40.000 --> 1:10:44.760
- So last question, LLVM logo is a dragon.
-
-1:10:44.760 --> 1:10:46.760
- You explained that this is because dragons
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-1:10:46.760 --> 1:10:50.320
- have connotations of power, speed, intelligence.
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-1:10:50.320 --> 1:10:53.320
- It can also be sleek, elegant, and modular,
-
-1:10:53.320 --> 1:10:56.280
- though you remove the modular part.
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-1:10:56.280 --> 1:10:58.920
- What is your favorite dragon related character
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-1:10:58.920 --> 1:11:01.480
- from fiction, video, or movies?
-
-1:11:01.480 --> 1:11:03.840
- So those are all very kind ways of explaining it.
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-1:11:03.840 --> 1:11:06.200
- Do you want to know the real reason it's a dragon?
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-1:11:06.200 --> 1:11:07.000
- Yeah.
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-1:11:07.000 --> 1:11:07.920
- Is that better?
-
-1:11:07.920 --> 1:11:11.040
- So there is a seminal book on compiler design
-
-1:11:11.040 --> 1:11:12.480
- called The Dragon Book.
-
-1:11:12.480 --> 1:11:16.280
- And so this is a really old now book on compilers.
-
-1:11:16.280 --> 1:11:22.040
- And so the Dragon logo for LLVM came about because at Apple,
-
-1:11:22.040 --> 1:11:24.720
- we kept talking about LLVM related technologies,
-
-1:11:24.720 --> 1:11:26.960
- and there's no logo to put on a slide.
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-1:11:26.960 --> 1:11:28.440
- And we're like, what do we do?
-
-1:11:28.440 --> 1:11:30.000
- And somebody's like, well, what kind of logo
-
-1:11:30.000 --> 1:11:32.160
- should a compiler technology have?
-
-1:11:32.160 --> 1:11:33.320
- And I'm like, I don't know.
-
-1:11:33.320 --> 1:11:37.280
- I mean, the dragon is the best thing that we've got.
-
-1:11:37.280 --> 1:11:40.600
- And Apple somehow magically came up with the logo.
-
-1:11:40.600 --> 1:11:43.240
- And it was a great thing, and the whole community
-
-1:11:43.240 --> 1:11:44.000
- rallied around it.
-
-1:11:44.000 --> 1:11:46.840
- And then it got better as other graphic designers got
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-1:11:46.840 --> 1:11:47.320
- involved.
-
-1:11:47.320 --> 1:11:49.280
- But that's originally where it came from.
-
-1:11:49.280 --> 1:11:50.080
- The story.
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-1:11:50.080 --> 1:11:53.960
- Is there dragons from fiction that you connect with?
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-1:11:53.960 --> 1:11:58.000
- That Game of Thrones, Lord of the Rings, that kind of thing?
-
-1:11:58.000 --> 1:11:59.120
- Lord of the Rings is great.
-
-1:11:59.120 --> 1:12:01.440
- I also like role playing games and things like computer
-
-1:12:01.440 --> 1:12:02.160
- role playing games.
-
-1:12:02.160 --> 1:12:03.600
- And so dragons often show up in there.
-
-1:12:03.600 --> 1:12:07.080
- But it really comes back to the book.
-
-1:12:07.080 --> 1:12:08.480
- Oh, no, we need a thing.
-
-1:12:08.480 --> 1:12:09.880
- We need a lot to do.
-
-1:12:09.880 --> 1:12:13.640
- And hilariously, one of the funny things about LLVM
-
-1:12:13.640 --> 1:12:19.400
- is that my wife, who's amazing, runs the LLVM foundation.
-
-1:12:19.400 --> 1:12:21.040
- And she goes to Grace Hopper, and is
-
-1:12:21.040 --> 1:12:22.480
- trying to get more women involved.
-
-1:12:22.480 --> 1:12:24.600
- And she's also a compiler engineer.
-
-1:12:24.600 --> 1:12:26.040
- So she's trying to get other women
-
-1:12:26.040 --> 1:12:28.120
- to get interested in compilers and things like this.
-
-1:12:28.120 --> 1:12:29.960
- And so she hands out the stickers.
-
-1:12:29.960 --> 1:12:34.240
- And people like the LLVM sticker because of Game of Thrones.
-
-1:12:34.240 --> 1:12:36.800
- And so sometimes culture has this helpful effect
-
-1:12:36.800 --> 1:12:41.040
- to get the next generation of compiler engineers engaged
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-1:12:41.040 --> 1:12:42.320
- with the cause.
-
-1:12:42.320 --> 1:12:43.240
- OK, awesome.
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-1:12:43.240 --> 1:12:44.680
- Grace, thanks so much for talking with us.
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-1:12:44.680 --> 1:13:07.440
- It's been great talking with you.
-