8 ms·

An Apple ISA is coming

278 points by samps 11y ago

hexscrews 11y ago
This seems a bit like click bait. It holds no substantial information. They might as well have summed up the article with, One day, apple will make their own processor. That's all it says.
- blazespin 11y ago
  To be fair, It says a wee bit more, it says apple has an llvm IR layer and a semantic gap exists with arm -> so it'll be both easier and necessary to create their own ISA layer. I'd really like to know the details behind the semantic gap, though. That was annoyingly vague and really is the premise of the entire argument.
- coldtea 11y ago
  Yeah, like "War And Peace" is about Russia in the times of Napoleon, and all "The Art of Computer Programming" says is "here is a bunch of algorithms".
- octo_t 11y ago
  "One day, apple will make their own processor." -> one day in the past. Apple already make their own processors.
raverbashing 11y ago
Though the arguments are interesting, I'm not convinced Sure, the semantic gap exists. But ARM and x86 have evolved and have overcome a lot of difficulties. People like to bash x86 but it has a big advantage: it's compact. ARM Thumb is compact but not so much. Also remember how big the last 'new ISA' (Itanium) success was? Compiler and processor front-end beat "perfect ISA" today
- simonh 11y ago
  The reason other ISAs have failed to get traction is compatibility. They couldn't run any existing binaries, and everyone wanting to use it would have to develop and adopt new tools. But Apple don't care about interoperability and completely control the entire software tools and distribution stack from top to bottom. They don't have to ask anyone else to do anything at all that they aren't doing already. No previous ISA vendor has even been in that position. Not even IBM with their mainframes. Furthermore the architecture of LLVM decouples it from particular processor architectures in ways that previous compiler architectures didn't, greatly easing the migration process at a technical level. But what's the benefit? Maybe a few percent speed/power efficiency boost? We've already seen that Apple will go to extraordinary lengths for a few percent improved performance, particularly when it comes to power efficiency. A few percent here, a few more there and soon you're talking an hour+ extra battery life. I think this is highly plausible. There just doesn't seem to be any particular reason why they wouldn't do it, and plenty of reasons why they would.
  - sklogic 11y ago
    > No previous ISA vendor has even been in that position. Remember the transition from VAX to Alpha? And they kept the binary and source compatibility in quite an inventive way (with both binary translation and by making MACRO32 just another high level language).
  - planteen 11y ago
    > Furthermore the architecture of LLVM decouples it from particular processor architectures in ways that previous compiler architectures didn't, greatly easing the migration process at a technical level. How is LLVM IR (which I am told is arch specific) different from GCC with RTL?
- sklogic 11y ago
  New ISAs keep appearing - in the GPU world nobody cares about any backward compatibility. Domain-specific ISAs make a lot of sense, and given the growing diversity of the Apple devices needs, they may really be ready to explore this possibility.
- mda 11y ago
  Itanium is 20 year old technology, A lot of things changed since. I wouldn't be surprised if they come up with a completely new ISA and produce their own chips now. If they can squeeze a few more dollars per device because of a such move, with the added bonus of more efficient and faster operation they will do it. Margins is the only important thing for Apple, nothing else matters.
- pcwalton 11y ago
  > People like to bash x86 but it has a big advantage: it's compact. x86-64 isn't. I've measured this: the average instruction length is just about 4 bytes. REX prefixes add up quick.
  - 1amzave 11y ago
    Is that really the definitive metric though? Seems like you'd want to compare overall program-text size between equivalent binaries for x86[-64] and $otherarch (i.e. x86 may be able to get away with fewer of those ~same-size instructions due to each of them doing slightly more on average).
omarforgotpwd 11y ago
Given the effort put into engineering support for bitcode in iOS 9, it's clear that the processor's instruction set is definitely going to change at some point. The only question is when. I wouldn't be surprised if these new processors were unveiled about 8 and a half hours from now.
- Jerry2 11y ago
  >I wouldn't be surprised if these new processors were unveiled about 8 and a half hours from now. I believe that we will see the new processor architecture in the next Apple Watch, not the next iPhone. I think A9, that will be unveiled later today, will be an improvement over A8 but it will not be a radical improvement and will not contain a new ISA. It will have improved ARM cores. Apple also doesn't require bitcode for iOS apps right now. They suggest you add them but don't require them. They're required for watchOS apps. Once Apple starts requiring bitcode for iOS, within a year or two you can expect some radical Apple CPUs for iPhone/iPad.
gchadwick 11y ago
It is a common theme in computer architecture for someone to say, 'look I have an awesome new architecture all you need is a clever compiler to make it work'. None of them really pan out (other than in specific applications, you could argue GPGPU is as an example, though that appeared more by accident than by design). Apple would need a very good reason to produce their own ISA. Sure they like to do many things in house but they don't do everything themselves. The resources required to produce and support a whole new ISA are a major investment, they're only going to do it if in the long run is cheaper than paying for an ARM architecture license. I just don't see a solid argument that a custom ISA and shiny new compiler would give them much (if indeed anything). Whilst they may be shipping LLVM IR for the watch apps rather than ARM code I think this is just so they can target the compile for a specific processor. Each one has its own performance quirks and especially in such a power sensitive environment it would make sense to do specific targetting.
- simonh 11y ago
  I don't see why a new compiler would be necessary. It's unlikely they'd completely throw out the whole ARM ISA and replace it with something completely different in one go. More likely, they'll gradually add new instructions and mutate the characteristics of existing instructions over time. LLVM IR isn't completely ISA agnostic, a lot of ISA specific assumptions are still baked into it, but gradual iterative improvement is Apple's speciality. A couple of new instructions this year, deprecate a few old one next, and in 5 years time you've got a new ISA that's barely recognizably ARM any more yet each step along the way is just an incremental and largely backwards compatible change.
  - gchadwick 11y ago
    > I don't see why a new compiler would be necessary. It's unlikely they'd completely throw out the whole ARM ISA and replace it with something completely different in one go. More likely, they'll gradually add new instructions and mutate the characteristics of existing instructions over time Well this is exactly the point. They cannot do this the license will not permit them to alter the architecture it's all or nothing (indeed if the new ISA was too ARM like the lawyers would be sure to come knocking). I'm sure the could reuse quite a lot of compiler technology but the entire point of the article is by doing clean slate ISA design you can do something radical and get gains. Whether this is true is unclear, but it would require some serious work on the compiler. Producing their own conventional ISA would seem to be pointless as it wouldn't give them anything vs ARM (or indeed x86).
deleted 11y ago
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em3rgent0rdr 11y ago
LLVM "owned" by Apple? Can't really "own" open-source.
- egil 11y ago
  I reckon the authors point is that they control how they use it. They might not own it all (but they sure hold the copyright to much of it), but no other entity outside of their control is going to pull the rug from under their feet.
- fab13n 11y ago
  What's the relevant definition of "owned" here? As long as Apple can modify LLVM however it wants, and as long as it's sure no corporate actor can restrict access rights to it in the future, it effectively owns it, altough not exclusively. Having exclusive rights on a strategic business brick is important when this brick is enough to give someone else a stronghold on the whole vertical market. Although having a good compilers is one of the many requirements in Apple's business model, it's neither the defining feature, nor what competitors miss in order to threaten Apple. So yes, in this context, Apple non-exclusively owns LLVM.
  - noja 11y ago
    owns is the wrong word. No need to redefine it to fit the sentence, they should have chosen a different word.
    - geoff-codes 11y ago
      Perhaps the word is 'pwn'?
- sklogic 11y ago
  To some extent, it does own it. Ever tried to push even a mildly controversial patch to LLVM or Clang upstream? If Apple guys are against it, it's a full stop, no matter how many other parties are interested. And their reasons to be against a particular patch are often as simple as that it'll break compatibility with their internal, unpublished changes to LLVM. Learned it the hard way...
hyperpallium 11y ago
Getting rid of accumulated cruft would simplify decode logic. Customize it for iOS. Siliconize common functions. Apple doesn't have to worry about standards, backcompatibility or adoption. If they have noticed unneccesary inefficiencies, they can fix them.
deleted 11y ago
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fulafel 11y ago
This "get freedom from binary compatibility by shipping binaries as compiler IR" concept is a venerable one and has been done many times with VLIW machines: See here, https://scholar.google.com/scholar?hl=en&q=A+Technique+for+Object+Code+Compatibility+in+VLIW https://scholar.google.com/scholar?hl=en&q=A+Technique+for+O... (Not to mention earlier examples like AS/400, P-code etc) I think the Mill was doing this too?
joosters 11y ago
I can't see this as a definitive sign that Apple are going to introduce a new ISA. Instead, this gives them flexibility. They can switch ISAs (e.g. to a new ARM revision, it doesn't have to be an Apple-specific one though) without authors having to recompile their code for all platforms. It also allows Apple to support multiple ISAs without code bloat - the app store can download the correct binary to your phone, just like they now can send only the correct size images. I don't know how abstract the LLVM IR is - can you take IR and compile it to two wildly different ISAs, (say) x86 and ARM, and get full optimisation on both? Or is it more limited, e.g. allowing you to compile to ARM version x and ARM version y (e.g. if version 'y' supports some new SIMD instructions).
- HappyTypist 11y ago
  LLVM converts your input language into the intermediate representation (LLVM IR) with a frontend. Then, a backend takes IR and spits out code for an ISA. IR is ISA agnostic. Compiling the same code to x86 and ARM will have the same IR, it's only the backend step that's different. Thus, of course you can take IR "meant for ARM" and compile it to "x86" and get full optimisation. The IR isn't meant for ARM anyway, IR is just IR.
  - gchadwick 11y ago
    > Compiling the same code to x86 and ARM will have the same IR This is incorrect. Clang has specific code paths (producing different IR) for x86 and ARM, specifically around calling conventions but I'm sure there are more.
  - riscy 11y ago
    > IR is ISA agnostic It's absolutely ISA specific and this target independence pipe dream keeps being repeated on HN. Just search the LLVM documentation for "target specific."
haberman 11y ago
It's widely disputed that LLVM bitcode is actually ISA-agnostic. There is a HN comment quoting Chris Lattner as saying that CPU independence isn't really the point of bitcode apps (I'd find it now but I'm on mobile). The thought is that it has a lot more to do with the ability to re-optimize.
- misterdata 11y ago
  I believe it's here: https://news.ycombinator.com/item?id=9728162 https://news.ycombinator.com/item?id=9728162
legulere 11y ago
This has been stated before: LLVM Bitcode is architecture specific. It's dependent on the architectures ABI and can contain inline assembly. There are LLVM targets with corresponding ABIs that are nonspecific to architectures like PNaCL but Apple is not using them Things Apple can do with bitcode: Produce binaries optimized for different ARM processors. Reoptimize with new versions of LLVM as soon as they are available. Use a big database of LLVM IR to tweak optimizations. Keep some optimizations secret and not even publish binaries doing them. The biggest argument IMO that speaks against an Apple ISA is that they would have to rewrite tons of hand tuned assembly code.
- geoff-codes 11y ago
  > There are LLVM targets with corresponding ABIs that are nonspecific to architectures like PNaCL but Apple is not using them They do indeed support LLVM IR target(s) that are, in fact, much more architecturally-nonspecific than PNaCl, namely the spir[64]-unknown-unknown target. See https://github.com/KhronosGroup/SPIR https://github.com/KhronosGroup/SPIR and /System/Library/Frameworks/OpenCL.framework/Versions/A/Libraries/openclc (on a Mac, since 10.7). I don't know if bitcode with this target triple is necessarily suitable for the Apple Watch, however.
  - bbatha 11y ago
    SPIR is basically portable gpu assembly. I wouldn't count it as an architecturally-nonspecific target.
    - wmobit 11y ago
      It's really not. It's barely an abstraction over LLVM IR
- iso8859-1 11y ago
  Since all modern CPUs have a ton of microcode, would it be hard to emulate the x86 when needed, and retain backwards compatibility like that?
rkangel 11y ago
This article points to another bit of the technology stack that Apple doesn't own - LLVM IR. LLVM is open source and therefore doesn't require licensing unlike the ARM Instruction Set, but it's another thing they don't perfectly control and they're happy with that. Developing a new ISA would be extremely expensive, and they'd have to have a really good reason for doing it. The post doesn't suggest why it would be beneficial, merely extrapolates a pattern.
- RegW 11y ago
  > This article points to another bit of the technology stack that Apple doesn't own - LLVM IR. Hmm, I saw the "LLVM owned since ~2005". What exactly does the article mean by "owned"? Perhaps, Apple owns it in the same way that all of us do, or perhaps the article just needs a little more work.
- leoedin 11y ago
  According to Wikipedia Apple hired Chris Lattner, one of the original authors of LLVM, in 2005. (https://en.wikipedia.org/wiki/LLVM https://en.wikipedia.org/wiki/LLVM) So they don't own it, but they do employ some of the most knowledgeable developers of the project. They almost certainly have control over the direction it takes, and could easily develop features behind closed doors.
- Rotten194 11y ago
  Apple can also fork LLVM if they want to assert more control.
dsjoerg 11y ago
In case you were wondering, like I was: http://google.com/search?q=what+is+an+isa http://google.com/search?q=what+is+an+isa
Aissen 11y ago
We'll see an Apple GPU IP in iPhones/iPads before a new ISA.
spiralpolitik 11y ago
To understand Apple today you have to look to the past. Apple ended up being stuck with Motorola's inablity to deliver faster PowerPC chips. Whole product lines were delayed, or not possible. Effectively they gave control on when they could ship new product to a third party. 10 years later they are now in the same position with Intel. If Intel delays the next version of its product line by six months then Apple has to put things on hold. This is bad for a company like Apple as it could cause them to miss out on potentially lucrative periods (back to School, the Holiday season etc). Ultimately I suspect in the very near term we will see Apple move off Intel, first for the laptops. LLVM IR would fit this strategy better than fat binaries as Apple would not have to wait until developers recompile. They can have the entire App Store available on day 1 of a product release.
- tw04 11y ago
  And if a company with as much experience and expertise as Intel misses their ship dates, what on earth makes Apple think they can do better? I could see an argument for cutting cost by eliminating the margin that Intel dictates... but even that assumes that you can find a third party to manufacture the chips at a rate that is low enough to both cover the IP Intel has in their chips, and the manufacturing cost itself.
  - Tloewald 11y ago
    Well, first of all Apple could do it and fail. They're done that before. They're confident/arrogant/audacious enough to try things that they can't pull off. Also, they could take a two-pronged approach -- cherry-pick talent from Intel, nVidia, etc. and offer them the opportunity to leapfrog baggage from the past. How much of the difficulty of moving the x86 platform forward is a result of the ludicrous amount of cruft? Grabbing a few of the smartest people and narrowing your focus to an easier problem gets you a long way. Apple has managed to outpace the entire industry (including Intel) with its customized ARM cores (getting to 64-bit over a year ahead of everyone, and take a look at benchmarks between Apple's Ax CPUs and rivals usually running at far higher clocks with more RAM and sucking more power), and it got there by cherry-picking talent, omitting stuff it didn't need, focusing on design, and treating fabs as a commodity. Looks like interesting times ahead.
geoff-codes 11y ago
I don't think this holds water at all. The crux of the article is: > ...one last gap remains in the middle of this stack of system exclusivity: Apple licenses the instruction set architecture for its mobile devices from ARM. But Apple already not only designs the own SoCs independently already, they regularly add their own opcodes to the ARM instruction sets they license, as they see fit. The alternative to not licensing from ARM, even if they "invented their own ISA", would be to pay an exorbitant sum in royalties to ARM and every other patent-holder whose technology they might dare use in their chip. So paying ARM for their technology in one go just makes the most economical/legal sense.
Tloewald 11y ago
Very insightful little post. In theory Apple could start evolving their ISA over time alongside everything else because LLVM gives them an abstraction layer. (Everyone else could do this too of course.)
hitlin37 11y ago
trying to understand a bit more about bitcode concept. Since a developer submits a bitcode for apple watch, does that mean he can't optimize his own app for performance? FWIK, on android you can still optimize your app at assembly level and i think that's what motivates developers at times. Remember the iphone camera high speed shot app, that was hand coded to be fast on iphone.
- monocasa 11y ago
  Bitcode can contain inline assembly still. Additionally, bitcode is significantly more tied to the target architecture than the author is assuming.
abalone 11y ago
The key sentence is: "the [current] architecture wastes time and energy rediscovering facts that the compiler already knew." If Apple does something here it's going to be for the watch, not Macs. Pushing the envelope of efficiency for the watch is where it becomes worth it to make this kind of (otherwise insane) investment. It's also a relatively simpler stack, so more feasible.
herp_derp 11y ago
For Apple to develop an ISA they would have to develop a CPU. Something they don't do inhouse. Up until now the CPUs have been designed by ARM. Cores like Swift for example were not developed at Apple, but rather at ARM. The likelihood of ARM releasing a chip into the wild with a non-ARM ISA is not all that great, since the ARM ISA is what ARM makes all of its living from. Until the day where Apple is capable of creating a CPU by themselves there will be no Apple ISA.
- dagw 11y ago
  For Apple to develop an ISA they would have to develop a CPU. Something they don't do inhouse. Apple owns PA Semiconductors which employs some of the smartest and most experienced CPU designers in the business.
frozenport 11y ago
Why didnt Apple just ask authors to submit source code?
- wolfgke 11y ago
  Because some developers prefer their own build system, which Apple really does not feel like to set up?
- oofabz 11y ago
  Many developers see Apple as a competitor, and Apple has had a long history of putting their platform's developers out of business. For example, iTunes destroyed the market for music library software.
protomyth 11y ago
I don't think they'll produce their own ISA. They have an architectural license from ARM, so why bother. But, Intel doesn't exactly produce chips that are helpful to Apple. Since Apple switch, Intel has gotten rid of third-party chipsets. This removed a lot of customization options and basically made life easier for Intel since they produce a fixed set of chips and you have to take them. Also, Intel's market differentiation of chip features probably doesn't help. Apple wants to provide a custom experience, and Apple building their own PC-class ARM chips will allow that. [edit: also Intel's paying people to produce Macbook Air clones probably didn't help]
- dlp211 11y ago
  It will never happen. There isn't an ARM chip out there that could handle the x86 emulation needed to move off of the platform. The only reason Apple was able to move off of PowerPC is because they were able emulate the ISA on x86.
  - protomyth 11y ago
    I don't think that will be the limiting factor. I can see Apple saying the new machines will run only newly compiled software. On that note, I get the feeling Bootcamp for ARM Macs would be interesting since it would be an ARM version of Windows.
    - mrpippy 11y ago
      The last time Microsoft made an ARM version of interactive/desktop Windows (Windows RT for the Surface/Surface 2), it didn't support legacy Win32 apps (native or x86 emulated). It was a huge flop; Win32 apps are still the overriding reason why anyone runs Windows. And now that Intel has gotten its act together with low-power SoCs, I don't see desktop Windows coming back to ARM any time soon. (yes, there is Windows 10 for ARM but only for IoT platforms, it doesn't support graphical apps)
      - protomyth 11y ago
clord 11y ago
I think the Mill team is a good acquisition target for Apple... Apple could swiftly switch their whole stack over and gain remarkable benefits. I can't think of another company that would even be able to switch to the mill line.
ChuckMcM 11y ago
I'm read this wondering if the author had any remembrance or understanding of the original CHRP/PReP fiasco (https://en.wikipedia.org/wiki/AIM_alliance https://en.wikipedia.org/wiki/AIM_alliance). That was a painful time for Apple. Given the nature of how ARM operates, and the fact that Apple has has a full ARM license (so could, at their leisure add special sauce in the instruction set if needed) that they would do a new ISA, they already did, x86-64 => ARM. The question for me is whether or not their desktop/laptop series moves that way or not. I've said for years a 12" MacBook Air running IOS would put a huge dent in the Chromebook market, and a 12" ARM based Air running IOS? Well that would be a pretty obvious move to me.
zvrba 11y ago
> a traditional von Neumann ISA like ARM incurs a semantic gap; the architecture wastes time and energy rediscovering facts that the compiler already knew. So thought the designers of Itanium too; it turned out that the compiler doesn't know sufficiently much for an architecture like Itanium. Were there any significant advances in compiler technology since then that would make it worthwhile to experiment with a new ISA?
tbrock 11y ago
Apple has owned part of ARM holdings as part of a joint venture between them and Acorn for decades now. That was one of the first pieces of the widget they had. Joke is on everyone making phones and servers: you are paying Apple already. From Wikipedia: "The company was founded in November 1990 as Advanced RISC. Machines Ltd and structured as a joint venture between Acorn Computers, Apple Computer (now Apple Inc.) and VLSI Technology."
- hajile 11y ago
  Apple sold their remaining stake in ARM back in 2003. http://appleinsider.com/articles/13/08/12/iphone-patent-wars-apples-11-billion-arm-injection-ignites-a-mobile-patent-race http://appleinsider.com/articles/13/08/12/iphone-patent-wars...
nikdaheratik 11y ago
Thought provoking, but I disagree with pretty much every conclusion. If there is anything they really need they can likely get ARM or Intel to put it in there, so building an ISA from scratch isn't going to gain them much. It's the same reason why they aren't going to become a cell-phone carrier even though that's another part of the vertical stack that they could try to get into: the cost/benefit makes it not worth it.
hajile 11y ago
Apple doesn't want their own ISA. MIPS was going for a song just a couple years ago and Apple decided not to buy. That was the best shot they'll have at their own ISA (they could go with RISCV, but they wouldn't own it).It is my belief that they got what they wanted by forcing ARM to switch to the ARMv8 ISA. New microarchitectures take 4 years or so to design. ARM announced the new ISA in 2011 and didn't have a shippable product until 2015 which is very typical. All the other implementers (eg. Qualcomm) have also not been able to ship until now (Qualcomm's custom Kryo doesn't hit until later this year). Apple shipped a better product in 2013 than A57 is today (ARM doesn't catch up until A72 later this year). To my knowledge, a licensee had never shipped a new ISA before the ISA designer up to this point. How did they get a chip designed, validated, tapped out, produced, integrated, and shipped out in 2 years? I believe that Apple looked into purchasing MIPS or designing a custom ISA, but was put off by the costs and headaches associated with moving ISAs (having already done this with the change from POWER to x86). Instead, they design an ISA that is incredibly close to MIPS and start implementing a micro-architecture. Once they reach the stage where they must make a decision about which ISA, they tell ARM to use their ISA or they will move to MIPS. This head-start also ARM is already somewhat threatened by Android having first-class support for MIPS. Having such a big player switch would be extremely threatening to them. The result would be an immediate caving. ARM would need to publish the ISA, but Apple would have a couple year head-start on implementing it (this head-start also puts Apple in a good competitive position relative to Android phone manufacturers). The rest is observable history. This may not accurately represent what really caused this series of events, but it does explain why Apple got a good chip out before ARM could release a bad one (ARM couldn't even get a smaller, easier chip out the door). It also explains why all the other chip companies hint at their surprise at Apple's early launch.
Quequau 11y ago
I'm pretty certain that lots of folks here are looking at this from an unproductive perspective. Robert Colwell from DARPA presented a talk at HotChips 2013 which was focused on post 'Moore's Law' technologies and he brings up specialized ISAs. Looking at the potential of Apple releasing chips with new ISAs from this perspective seems to me to make a lot more sense (to me at least). https://www.youtube.com/watch?v=JpgV6rCn5-g https://www.youtube.com/watch?v=JpgV6rCn5-g

278 points by samps 11y ago

This seems a bit like click bait. It holds no substantial information. They might as well have summed up the article with, One day, apple will make their own processor. That's all it says.

blazespin 11y ago
To be fair, It says a wee bit more, it says apple has an llvm IR layer and a semantic gap exists with arm -> so it'll be both easier and necessary to create their own ISA layer. I'd really like to know the details behind the semantic gap, though. That was annoyingly vague and really is the premise of the entire argument.
coldtea 11y ago
Yeah, like "War And Peace" is about Russia in the times of Napoleon, and all "The Art of Computer Programming" says is "here is a bunch of algorithms".
octo_t 11y ago
"One day, apple will make their own processor." -> one day in the past. Apple already make their own processors.

raverbashing 11y ago

Though the arguments are interesting, I'm not convinced Sure, the semantic gap exists. But ARM and x86 have evolved and have overcome a lot of difficulties. People like to bash x86 but it has a big advantage: it's compact. ARM Thumb is compact but not so much. Also remember how big the last 'new ISA' (Itanium) success was? Compiler and processor front-end beat "perfect ISA" today

simonh 11y ago
The reason other ISAs have failed to get traction is compatibility. They couldn't run any existing binaries, and everyone wanting to use it would have to develop and adopt new tools. But Apple don't care about interoperability and completely control the entire software tools and distribution stack from top to bottom. They don't have to ask anyone else to do anything at all that they aren't doing already. No previous ISA vendor has even been in that position. Not even IBM with their mainframes. Furthermore the architecture of LLVM decouples it from particular processor architectures in ways that previous compiler architectures didn't, greatly easing the migration process at a technical level. But what's the benefit? Maybe a few percent speed/power efficiency boost? We've already seen that Apple will go to extraordinary lengths for a few percent improved performance, particularly when it comes to power efficiency. A few percent here, a few more there and soon you're talking an hour+ extra battery life. I think this is highly plausible. There just doesn't seem to be any particular reason why they wouldn't do it, and plenty of reasons why they would.
- sklogic 11y ago
  > No previous ISA vendor has even been in that position. Remember the transition from VAX to Alpha? And they kept the binary and source compatibility in quite an inventive way (with both binary translation and by making MACRO32 just another high level language).
- planteen 11y ago
  > Furthermore the architecture of LLVM decouples it from particular processor architectures in ways that previous compiler architectures didn't, greatly easing the migration process at a technical level. How is LLVM IR (which I am told is arch specific) different from GCC with RTL?
sklogic 11y ago
New ISAs keep appearing - in the GPU world nobody cares about any backward compatibility. Domain-specific ISAs make a lot of sense, and given the growing diversity of the Apple devices needs, they may really be ready to explore this possibility.
mda 11y ago
Itanium is 20 year old technology, A lot of things changed since. I wouldn't be surprised if they come up with a completely new ISA and produce their own chips now. If they can squeeze a few more dollars per device because of a such move, with the added bonus of more efficient and faster operation they will do it. Margins is the only important thing for Apple, nothing else matters.
pcwalton 11y ago
> People like to bash x86 but it has a big advantage: it's compact. x86-64 isn't. I've measured this: the average instruction length is just about 4 bytes. REX prefixes add up quick.
- 1amzave 11y ago
  Is that really the definitive metric though? Seems like you'd want to compare overall program-text size between equivalent binaries for x86[-64] and $otherarch (i.e. x86 may be able to get away with fewer of those ~same-size instructions due to each of them doing slightly more on average).

omarforgotpwd 11y ago

Given the effort put into engineering support for bitcode in iOS 9, it's clear that the processor's instruction set is definitely going to change at some point. The only question is when. I wouldn't be surprised if these new processors were unveiled about 8 and a half hours from now.

Jerry2 11y ago
>I wouldn't be surprised if these new processors were unveiled about 8 and a half hours from now. I believe that we will see the new processor architecture in the next Apple Watch, not the next iPhone. I think A9, that will be unveiled later today, will be an improvement over A8 but it will not be a radical improvement and will not contain a new ISA. It will have improved ARM cores. Apple also doesn't require bitcode for iOS apps right now. They suggest you add them but don't require them. They're required for watchOS apps. Once Apple starts requiring bitcode for iOS, within a year or two you can expect some radical Apple CPUs for iPhone/iPad.

gchadwick 11y ago

It is a common theme in computer architecture for someone to say, 'look I have an awesome new architecture all you need is a clever compiler to make it work'. None of them really pan out (other than in specific applications, you could argue GPGPU is as an example, though that appeared more by accident than by design). Apple would need a very good reason to produce their own ISA. Sure they like to do many things in house but they don't do everything themselves. The resources required to produce and support a whole new ISA are a major investment, they're only going to do it if in the long run is cheaper than paying for an ARM architecture license. I just don't see a solid argument that a custom ISA and shiny new compiler would give them much (if indeed anything). Whilst they may be shipping LLVM IR for the watch apps rather than ARM code I think this is just so they can target the compile for a specific processor. Each one has its own performance quirks and especially in such a power sensitive environment it would make sense to do specific targetting.

simonh 11y ago
I don't see why a new compiler would be necessary. It's unlikely they'd completely throw out the whole ARM ISA and replace it with something completely different in one go. More likely, they'll gradually add new instructions and mutate the characteristics of existing instructions over time. LLVM IR isn't completely ISA agnostic, a lot of ISA specific assumptions are still baked into it, but gradual iterative improvement is Apple's speciality. A couple of new instructions this year, deprecate a few old one next, and in 5 years time you've got a new ISA that's barely recognizably ARM any more yet each step along the way is just an incremental and largely backwards compatible change.
- gchadwick 11y ago
  > I don't see why a new compiler would be necessary. It's unlikely they'd completely throw out the whole ARM ISA and replace it with something completely different in one go. More likely, they'll gradually add new instructions and mutate the characteristics of existing instructions over time Well this is exactly the point. They cannot do this the license will not permit them to alter the architecture it's all or nothing (indeed if the new ISA was too ARM like the lawyers would be sure to come knocking). I'm sure the could reuse quite a lot of compiler technology but the entire point of the article is by doing clean slate ISA design you can do something radical and get gains. Whether this is true is unclear, but it would require some serious work on the compiler. Producing their own conventional ISA would seem to be pointless as it wouldn't give them anything vs ARM (or indeed x86).

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em3rgent0rdr 11y ago

LLVM "owned" by Apple? Can't really "own" open-source.

egil 11y ago
I reckon the authors point is that they control how they use it. They might not own it all (but they sure hold the copyright to much of it), but no other entity outside of their control is going to pull the rug from under their feet.
fab13n 11y ago
What's the relevant definition of "owned" here? As long as Apple can modify LLVM however it wants, and as long as it's sure no corporate actor can restrict access rights to it in the future, it effectively owns it, altough not exclusively. Having exclusive rights on a strategic business brick is important when this brick is enough to give someone else a stronghold on the whole vertical market. Although having a good compilers is one of the many requirements in Apple's business model, it's neither the defining feature, nor what competitors miss in order to threaten Apple. So yes, in this context, Apple non-exclusively owns LLVM.
- noja 11y ago
  owns is the wrong word. No need to redefine it to fit the sentence, they should have chosen a different word.
  - geoff-codes 11y ago
    Perhaps the word is 'pwn'?
sklogic 11y ago
To some extent, it does own it. Ever tried to push even a mildly controversial patch to LLVM or Clang upstream? If Apple guys are against it, it's a full stop, no matter how many other parties are interested. And their reasons to be against a particular patch are often as simple as that it'll break compatibility with their internal, unpublished changes to LLVM. Learned it the hard way...

hyperpallium 11y ago

Getting rid of accumulated cruft would simplify decode logic. Customize it for iOS. Siliconize common functions. Apple doesn't have to worry about standards, backcompatibility or adoption. If they have noticed unneccesary inefficiencies, they can fix them.

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fulafel 11y ago

This "get freedom from binary compatibility by shipping binaries as compiler IR" concept is a venerable one and has been done many times with VLIW machines: See here, https://scholar.google.com/scholar?hl=en&q=A+Technique+for+Object+Code+Compatibility+in+VLIW https://scholar.google.com/scholar?hl=en&q=A+Technique+for+O... (Not to mention earlier examples like AS/400, P-code etc) I think the Mill was doing this too?

joosters 11y ago

I can't see this as a definitive sign that Apple are going to introduce a new ISA. Instead, this gives them flexibility. They can switch ISAs (e.g. to a new ARM revision, it doesn't have to be an Apple-specific one though) without authors having to recompile their code for all platforms. It also allows Apple to support multiple ISAs without code bloat - the app store can download the correct binary to your phone, just like they now can send only the correct size images. I don't know how abstract the LLVM IR is - can you take IR and compile it to two wildly different ISAs, (say) x86 and ARM, and get full optimisation on both? Or is it more limited, e.g. allowing you to compile to ARM version x and ARM version y (e.g. if version 'y' supports some new SIMD instructions).

HappyTypist 11y ago
LLVM converts your input language into the intermediate representation (LLVM IR) with a frontend. Then, a backend takes IR and spits out code for an ISA. IR is ISA agnostic. Compiling the same code to x86 and ARM will have the same IR, it's only the backend step that's different. Thus, of course you can take IR "meant for ARM" and compile it to "x86" and get full optimisation. The IR isn't meant for ARM anyway, IR is just IR.
- gchadwick 11y ago
  > Compiling the same code to x86 and ARM will have the same IR This is incorrect. Clang has specific code paths (producing different IR) for x86 and ARM, specifically around calling conventions but I'm sure there are more.
- riscy 11y ago
  > IR is ISA agnostic It's absolutely ISA specific and this target independence pipe dream keeps being repeated on HN. Just search the LLVM documentation for "target specific."

haberman 11y ago

It's widely disputed that LLVM bitcode is actually ISA-agnostic. There is a HN comment quoting Chris Lattner as saying that CPU independence isn't really the point of bitcode apps (I'd find it now but I'm on mobile). The thought is that it has a lot more to do with the ability to re-optimize.

misterdata 11y ago
I believe it's here: https://news.ycombinator.com/item?id=9728162 https://news.ycombinator.com/item?id=9728162

legulere 11y ago

This has been stated before: LLVM Bitcode is architecture specific. It's dependent on the architectures ABI and can contain inline assembly. There are LLVM targets with corresponding ABIs that are nonspecific to architectures like PNaCL but Apple is not using them Things Apple can do with bitcode: Produce binaries optimized for different ARM processors. Reoptimize with new versions of LLVM as soon as they are available. Use a big database of LLVM IR to tweak optimizations. Keep some optimizations secret and not even publish binaries doing them. The biggest argument IMO that speaks against an Apple ISA is that they would have to rewrite tons of hand tuned assembly code.

geoff-codes 11y ago
> There are LLVM targets with corresponding ABIs that are nonspecific to architectures like PNaCL but Apple is not using them They do indeed support LLVM IR target(s) that are, in fact, much more architecturally-nonspecific than PNaCl, namely the spir[64]-unknown-unknown target. See https://github.com/KhronosGroup/SPIR https://github.com/KhronosGroup/SPIR and /System/Library/Frameworks/OpenCL.framework/Versions/A/Libraries/openclc (on a Mac, since 10.7). I don't know if bitcode with this target triple is necessarily suitable for the Apple Watch, however.
- bbatha 11y ago
  SPIR is basically portable gpu assembly. I wouldn't count it as an architecturally-nonspecific target.
  - wmobit 11y ago
    It's really not. It's barely an abstraction over LLVM IR
iso8859-1 11y ago
Since all modern CPUs have a ton of microcode, would it be hard to emulate the x86 when needed, and retain backwards compatibility like that?

rkangel 11y ago

This article points to another bit of the technology stack that Apple doesn't own - LLVM IR. LLVM is open source and therefore doesn't require licensing unlike the ARM Instruction Set, but it's another thing they don't perfectly control and they're happy with that. Developing a new ISA would be extremely expensive, and they'd have to have a really good reason for doing it. The post doesn't suggest why it would be beneficial, merely extrapolates a pattern.

RegW 11y ago
> This article points to another bit of the technology stack that Apple doesn't own - LLVM IR. Hmm, I saw the "LLVM owned since ~2005". What exactly does the article mean by "owned"? Perhaps, Apple owns it in the same way that all of us do, or perhaps the article just needs a little more work.
leoedin 11y ago
According to Wikipedia Apple hired Chris Lattner, one of the original authors of LLVM, in 2005. (https://en.wikipedia.org/wiki/LLVM https://en.wikipedia.org/wiki/LLVM) So they don't own it, but they do employ some of the most knowledgeable developers of the project. They almost certainly have control over the direction it takes, and could easily develop features behind closed doors.
Rotten194 11y ago
Apple can also fork LLVM if they want to assert more control.

dsjoerg 11y ago

In case you were wondering, like I was: http://google.com/search?q=what+is+an+isa http://google.com/search?q=what+is+an+isa

Aissen 11y ago

We'll see an Apple GPU IP in iPhones/iPads before a new ISA.

spiralpolitik 11y ago

To understand Apple today you have to look to the past. Apple ended up being stuck with Motorola's inablity to deliver faster PowerPC chips. Whole product lines were delayed, or not possible. Effectively they gave control on when they could ship new product to a third party. 10 years later they are now in the same position with Intel. If Intel delays the next version of its product line by six months then Apple has to put things on hold. This is bad for a company like Apple as it could cause them to miss out on potentially lucrative periods (back to School, the Holiday season etc). Ultimately I suspect in the very near term we will see Apple move off Intel, first for the laptops. LLVM IR would fit this strategy better than fat binaries as Apple would not have to wait until developers recompile. They can have the entire App Store available on day 1 of a product release.

tw04 11y ago
And if a company with as much experience and expertise as Intel misses their ship dates, what on earth makes Apple think they can do better? I could see an argument for cutting cost by eliminating the margin that Intel dictates... but even that assumes that you can find a third party to manufacture the chips at a rate that is low enough to both cover the IP Intel has in their chips, and the manufacturing cost itself.
- Tloewald 11y ago
  Well, first of all Apple could do it and fail. They're done that before. They're confident/arrogant/audacious enough to try things that they can't pull off. Also, they could take a two-pronged approach -- cherry-pick talent from Intel, nVidia, etc. and offer them the opportunity to leapfrog baggage from the past. How much of the difficulty of moving the x86 platform forward is a result of the ludicrous amount of cruft? Grabbing a few of the smartest people and narrowing your focus to an easier problem gets you a long way. Apple has managed to outpace the entire industry (including Intel) with its customized ARM cores (getting to 64-bit over a year ahead of everyone, and take a look at benchmarks between Apple's Ax CPUs and rivals usually running at far higher clocks with more RAM and sucking more power), and it got there by cherry-picking talent, omitting stuff it didn't need, focusing on design, and treating fabs as a commodity. Looks like interesting times ahead.

geoff-codes 11y ago

I don't think this holds water at all. The crux of the article is: > ...one last gap remains in the middle of this stack of system exclusivity: Apple licenses the instruction set architecture for its mobile devices from ARM. But Apple already not only designs the own SoCs independently already, they regularly add their own opcodes to the ARM instruction sets they license, as they see fit. The alternative to not licensing from ARM, even if they "invented their own ISA", would be to pay an exorbitant sum in royalties to ARM and every other patent-holder whose technology they might dare use in their chip. So paying ARM for their technology in one go just makes the most economical/legal sense.

Tloewald 11y ago

Very insightful little post. In theory Apple could start evolving their ISA over time alongside everything else because LLVM gives them an abstraction layer. (Everyone else could do this too of course.)

hitlin37 11y ago

trying to understand a bit more about bitcode concept. Since a developer submits a bitcode for apple watch, does that mean he can't optimize his own app for performance? FWIK, on android you can still optimize your app at assembly level and i think that's what motivates developers at times. Remember the iphone camera high speed shot app, that was hand coded to be fast on iphone.

monocasa 11y ago
Bitcode can contain inline assembly still. Additionally, bitcode is significantly more tied to the target architecture than the author is assuming.

abalone 11y ago

The key sentence is: "the [current] architecture wastes time and energy rediscovering facts that the compiler already knew." If Apple does something here it's going to be for the watch, not Macs. Pushing the envelope of efficiency for the watch is where it becomes worth it to make this kind of (otherwise insane) investment. It's also a relatively simpler stack, so more feasible.

herp_derp 11y ago

For Apple to develop an ISA they would have to develop a CPU. Something they don't do inhouse. Up until now the CPUs have been designed by ARM. Cores like Swift for example were not developed at Apple, but rather at ARM. The likelihood of ARM releasing a chip into the wild with a non-ARM ISA is not all that great, since the ARM ISA is what ARM makes all of its living from. Until the day where Apple is capable of creating a CPU by themselves there will be no Apple ISA.

dagw 11y ago
For Apple to develop an ISA they would have to develop a CPU. Something they don't do inhouse. Apple owns PA Semiconductors which employs some of the smartest and most experienced CPU designers in the business.

frozenport 11y ago

Why didnt Apple just ask authors to submit source code?

wolfgke 11y ago
Because some developers prefer their own build system, which Apple really does not feel like to set up?
oofabz 11y ago
Many developers see Apple as a competitor, and Apple has had a long history of putting their platform's developers out of business. For example, iTunes destroyed the market for music library software.

protomyth 11y ago

I don't think they'll produce their own ISA. They have an architectural license from ARM, so why bother. But, Intel doesn't exactly produce chips that are helpful to Apple. Since Apple switch, Intel has gotten rid of third-party chipsets. This removed a lot of customization options and basically made life easier for Intel since they produce a fixed set of chips and you have to take them. Also, Intel's market differentiation of chip features probably doesn't help. Apple wants to provide a custom experience, and Apple building their own PC-class ARM chips will allow that. [edit: also Intel's paying people to produce Macbook Air clones probably didn't help]

dlp211 11y ago
It will never happen. There isn't an ARM chip out there that could handle the x86 emulation needed to move off of the platform. The only reason Apple was able to move off of PowerPC is because they were able emulate the ISA on x86.
- protomyth 11y ago
  I don't think that will be the limiting factor. I can see Apple saying the new machines will run only newly compiled software. On that note, I get the feeling Bootcamp for ARM Macs would be interesting since it would be an ARM version of Windows.
  - mrpippy 11y ago
    The last time Microsoft made an ARM version of interactive/desktop Windows (Windows RT for the Surface/Surface 2), it didn't support legacy Win32 apps (native or x86 emulated). It was a huge flop; Win32 apps are still the overriding reason why anyone runs Windows. And now that Intel has gotten its act together with low-power SoCs, I don't see desktop Windows coming back to ARM any time soon. (yes, there is Windows 10 for ARM but only for IoT platforms, it doesn't support graphical apps)
    - protomyth 11y ago

clord 11y ago

I think the Mill team is a good acquisition target for Apple... Apple could swiftly switch their whole stack over and gain remarkable benefits. I can't think of another company that would even be able to switch to the mill line.

ChuckMcM 11y ago

I'm read this wondering if the author had any remembrance or understanding of the original CHRP/PReP fiasco (https://en.wikipedia.org/wiki/AIM_alliance https://en.wikipedia.org/wiki/AIM_alliance). That was a painful time for Apple. Given the nature of how ARM operates, and the fact that Apple has has a full ARM license (so could, at their leisure add special sauce in the instruction set if needed) that they would do a new ISA, they already did, x86-64 => ARM. The question for me is whether or not their desktop/laptop series moves that way or not. I've said for years a 12" MacBook Air running IOS would put a huge dent in the Chromebook market, and a 12" ARM based Air running IOS? Well that would be a pretty obvious move to me.

zvrba 11y ago

> a traditional von Neumann ISA like ARM incurs a semantic gap; the architecture wastes time and energy rediscovering facts that the compiler already knew. So thought the designers of Itanium too; it turned out that the compiler doesn't know sufficiently much for an architecture like Itanium. Were there any significant advances in compiler technology since then that would make it worthwhile to experiment with a new ISA?

tbrock 11y ago

Apple has owned part of ARM holdings as part of a joint venture between them and Acorn for decades now. That was one of the first pieces of the widget they had. Joke is on everyone making phones and servers: you are paying Apple already. From Wikipedia: "The company was founded in November 1990 as Advanced RISC. Machines Ltd and structured as a joint venture between Acorn Computers, Apple Computer (now Apple Inc.) and VLSI Technology."

hajile 11y ago
Apple sold their remaining stake in ARM back in 2003. http://appleinsider.com/articles/13/08/12/iphone-patent-wars-apples-11-billion-arm-injection-ignites-a-mobile-patent-race http://appleinsider.com/articles/13/08/12/iphone-patent-wars...

nikdaheratik 11y ago

Thought provoking, but I disagree with pretty much every conclusion. If there is anything they really need they can likely get ARM or Intel to put it in there, so building an ISA from scratch isn't going to gain them much. It's the same reason why they aren't going to become a cell-phone carrier even though that's another part of the vertical stack that they could try to get into: the cost/benefit makes it not worth it.

hajile 11y ago

Apple doesn't want their own ISA. MIPS was going for a song just a couple years ago and Apple decided not to buy. That was the best shot they'll have at their own ISA (they could go with RISCV, but they wouldn't own it).It is my belief that they got what they wanted by forcing ARM to switch to the ARMv8 ISA. New microarchitectures take 4 years or so to design. ARM announced the new ISA in 2011 and didn't have a shippable product until 2015 which is very typical. All the other implementers (eg. Qualcomm) have also not been able to ship until now (Qualcomm's custom Kryo doesn't hit until later this year). Apple shipped a better product in 2013 than A57 is today (ARM doesn't catch up until A72 later this year). To my knowledge, a licensee had never shipped a new ISA before the ISA designer up to this point. How did they get a chip designed, validated, tapped out, produced, integrated, and shipped out in 2 years? I believe that Apple looked into purchasing MIPS or designing a custom ISA, but was put off by the costs and headaches associated with moving ISAs (having already done this with the change from POWER to x86). Instead, they design an ISA that is incredibly close to MIPS and start implementing a micro-architecture. Once they reach the stage where they must make a decision about which ISA, they tell ARM to use their ISA or they will move to MIPS. This head-start also ARM is already somewhat threatened by Android having first-class support for MIPS. Having such a big player switch would be extremely threatening to them. The result would be an immediate caving. ARM would need to publish the ISA, but Apple would have a couple year head-start on implementing it (this head-start also puts Apple in a good competitive position relative to Android phone manufacturers). The rest is observable history. This may not accurately represent what really caused this series of events, but it does explain why Apple got a good chip out before ARM could release a bad one (ARM couldn't even get a smaller, easier chip out the door). It also explains why all the other chip companies hint at their surprise at Apple's early launch.

Quequau 11y ago

I'm pretty certain that lots of folks here are looking at this from an unproductive perspective. Robert Colwell from DARPA presented a talk at HotChips 2013 which was focused on post 'Moore's Law' technologies and he brings up specialized ISAs. Looking at the potential of Apple releasing chips with new ISAs from this perspective seems to me to make a lot more sense (to me at least). https://www.youtube.com/watch?v=JpgV6rCn5-g https://www.youtube.com/watch?v=JpgV6rCn5-g