3 ms·

Not surprising to me to see CPU instructions being added for widely used use cases. Basically, a CPU instruction set maker's job is to perform clustering of the

by est31 6y ago

Not surprising to me to see CPU instructions being added for widely used use cases. Basically, a CPU instruction set maker's job is to perform clustering of the tasks that the CPUs do and accelerate commonly used tasks. If people do a lot of AES, the instruction set maker adds AES extensions. If people do a lot of CRC, they add CRC instructions. If people convert doubles to integers all day in a very JS specific way, then that's the instruction they add.

orf 6y ago
Can you name any other instructions with the name of a programming language in the actual instruction name? No? Then it seems way more specific than the other examples you listed. So specific that it’s only applicable to a single language and that language is in the instruction name. That’s surprising, like finding an instruction called “python GIL release”.
- diggan 6y ago
  Not necessarily programming languages (in similar vain as what est31 said) but cryptography has made its way into instructions, see SHA1RNDS4, SHA1NEXTE, SHA1MSG1 and more. They are not general cryptographic primitives but specific instructions for computing a specific cryptographic hash, just because SHA became popular. Also has SHA in it's name :)
  - est31 6y ago
    Yes, the examples I quoted AES and CRC all have dedicated instructions in x86 processors (at least the ones that implement the extensions). https://en.wikipedia.org/wiki/AES_instruction_set#Instructions https://en.wikipedia.org/wiki/AES_instruction_set#Instructio... https://www.felixcloutier.com/x86/crc32 https://www.felixcloutier.com/x86/crc32 As does ARM: https://developer.arm.com/documentation/ddi0514/g/introduction/about-the-cortex-a57-processor-cryptography-engine https://developer.arm.com/documentation/ddi0514/g/introducti... https://developer.arm.com/documentation/dui0801/g/A32-and-T32-Instructions/CRC32 https://developer.arm.com/documentation/dui0801/g/A32-and-T3... You could say that these are language-agnostic, and indeed they are, but in a certain way they are more specific than the JavaScript operation, because the JavaScript operation is likely used in many different algorithms. I'd argue that from the point of view of a chip manufacturer, the difference matters only little. Both are tasks that the CPUs do often and thus cost energy. By implementing them natively, the CPU manufacturer reduces the cost of those workflows for their clients.
    - neerajsi 6y ago
      More importantly, the customers of the cpu vendors use benchmarks to evaluate potential chip suppliers, and Js benchmarks are near the top of the list for ARM now. Everyone from the OS vendor to the compiler authors to ARM itself are looking at the same operations, so instructions like this get requested and added. There are also funny xaflag, axflag instructions in armv8 specifically to speed up x86 emulation on arm64. I believe they were added at the request of the msft emulator team.
- Someone 6y ago
  CPUs with the name of a programming language exist: - https://en.wikipedia.org/wiki/Lisp_machine https://en.wikipedia.org/wiki/Lisp_machine - https://en.wikipedia.org/wiki/Java_processor https://en.wikipedia.org/wiki/Java_processor These are examples of https://en.wikipedia.org/wiki/High-level_language_computer_architecture https://en.wikipedia.org/wiki/High-level_language_computer_a....
- aardvark179 6y ago
  Off the top of my head, and ignoring the Java bytecode instructions added at one point, no. I can however think of quite a lot of crypto related instructions, and many CPU and MMU features aimed at very specific language features such as garbage collection.
- est31 6y ago
  In addition to what the sibling comments said, note that "Python GIL release" is a very high level concept and how the GIL is implemented can change over time. It interacts with how the OS implements locking. FJCVTZS on the other hand is a (mostly) pure function with well defined inputs and outputs, and will likely be useful for Javascript implementations for a long time. Will JS be around in 10 years? Very likely. So ARM adds an instruction for it. The people at ARM have likely put a lot of thought behind this, trying to find the places where they, as instruction set vendor, can help making JS workflows easier. And btw, I'm pretty sure that if python has some equally low hanging fruit to make execution faster, and python enjoys equally large use, ARM will likely add an instruction for it as well.
- tedunangst 6y ago
  If they had named the instruction FCVTZSO, would you care? Would you even know?
- FullyFunctional 6y ago
  Well if you go far enough back, it was not usual to find special allowance for programming language constructs (like procedure linkage that supported display, useful for languages like Pascal with nested procedures etc). The reason you don't find this is that all "modern" processors designed since ~ 1980 are machines to run ... C as the vast majority (up until ~ Java) of all software on desktops and below were written in C. This also has implications for security as catching things like out of bound access or integer overflow isn't part of C so doing it comes with an explicit cost even when it's cheap in hardware.
- afiori 6y ago
  Based on other comments: The Javascript spec decided to standardize float operations and (in part) opted for whatever x86 did. ARM had different floating point profiles so ARM processors had to emulate in software intel's operations. Thus ARM decided to simply implement intel's operation as an instruction and called it by the relevant use case.
regularfry 6y ago
With reduced instruction sets, though, the idea is to provide common subparts and make them fast rather than dedicated instructions. While it's not odd to see dedicated instructions in CPUs in general, it's jarring to see if you're familiar with ARM chips from back when they had 25 instructions total.
- est31 6y ago
  Yeah that's how RISC vs CISC is taught in class, I've heard that same thing. I think it's an outdated paradigm though, if it's not been wrong all along. A CISC chip can still officially support instructions, but deprecate them and implement them very slowly in microcode, as is done with some x86 instructions. And a RISC chip manufacturer might just have used this phrase as a marketing line because designing RISC chips is easier than starting with a monster that has tons of instructions, and they needed some catchy phrase to market their alternative. They then get into the gradual process of making their customers happier one by one by adding special, mostly cold, silicon targeted for special workflows, like in this instance. Ultimately, the instruction set isn't that relevant anyways, what's more relevant is how the microcode can handle speculative execution for common workflows. There's a great podcast/interview from the x86 specification author: https://www.youtube.com/watch?v=Nb2tebYAaOA https://www.youtube.com/watch?v=Nb2tebYAaOA

by est31 6y ago

orf 6y ago

Can you name any other instructions with the name of a programming language in the actual instruction name? No? Then it seems way more specific than the other examples you listed. So specific that it’s only applicable to a single language and that language is in the instruction name. That’s surprising, like finding an instruction called “python GIL release”.

diggan 6y ago
Not necessarily programming languages (in similar vain as what est31 said) but cryptography has made its way into instructions, see SHA1RNDS4, SHA1NEXTE, SHA1MSG1 and more. They are not general cryptographic primitives but specific instructions for computing a specific cryptographic hash, just because SHA became popular. Also has SHA in it's name :)
- est31 6y ago
  Yes, the examples I quoted AES and CRC all have dedicated instructions in x86 processors (at least the ones that implement the extensions). https://en.wikipedia.org/wiki/AES_instruction_set#Instructions https://en.wikipedia.org/wiki/AES_instruction_set#Instructio... https://www.felixcloutier.com/x86/crc32 https://www.felixcloutier.com/x86/crc32 As does ARM: https://developer.arm.com/documentation/ddi0514/g/introduction/about-the-cortex-a57-processor-cryptography-engine https://developer.arm.com/documentation/ddi0514/g/introducti... https://developer.arm.com/documentation/dui0801/g/A32-and-T32-Instructions/CRC32 https://developer.arm.com/documentation/dui0801/g/A32-and-T3... You could say that these are language-agnostic, and indeed they are, but in a certain way they are more specific than the JavaScript operation, because the JavaScript operation is likely used in many different algorithms. I'd argue that from the point of view of a chip manufacturer, the difference matters only little. Both are tasks that the CPUs do often and thus cost energy. By implementing them natively, the CPU manufacturer reduces the cost of those workflows for their clients.
  - neerajsi 6y ago
    More importantly, the customers of the cpu vendors use benchmarks to evaluate potential chip suppliers, and Js benchmarks are near the top of the list for ARM now. Everyone from the OS vendor to the compiler authors to ARM itself are looking at the same operations, so instructions like this get requested and added. There are also funny xaflag, axflag instructions in armv8 specifically to speed up x86 emulation on arm64. I believe they were added at the request of the msft emulator team.
Someone 6y ago
CPUs with the name of a programming language exist: - https://en.wikipedia.org/wiki/Lisp_machine https://en.wikipedia.org/wiki/Lisp_machine - https://en.wikipedia.org/wiki/Java_processor https://en.wikipedia.org/wiki/Java_processor These are examples of https://en.wikipedia.org/wiki/High-level_language_computer_architecture https://en.wikipedia.org/wiki/High-level_language_computer_a....
aardvark179 6y ago
Off the top of my head, and ignoring the Java bytecode instructions added at one point, no. I can however think of quite a lot of crypto related instructions, and many CPU and MMU features aimed at very specific language features such as garbage collection.
est31 6y ago
In addition to what the sibling comments said, note that "Python GIL release" is a very high level concept and how the GIL is implemented can change over time. It interacts with how the OS implements locking. FJCVTZS on the other hand is a (mostly) pure function with well defined inputs and outputs, and will likely be useful for Javascript implementations for a long time. Will JS be around in 10 years? Very likely. So ARM adds an instruction for it. The people at ARM have likely put a lot of thought behind this, trying to find the places where they, as instruction set vendor, can help making JS workflows easier. And btw, I'm pretty sure that if python has some equally low hanging fruit to make execution faster, and python enjoys equally large use, ARM will likely add an instruction for it as well.
tedunangst 6y ago
If they had named the instruction FCVTZSO, would you care? Would you even know?
FullyFunctional 6y ago
Well if you go far enough back, it was not usual to find special allowance for programming language constructs (like procedure linkage that supported display, useful for languages like Pascal with nested procedures etc). The reason you don't find this is that all "modern" processors designed since ~ 1980 are machines to run ... C as the vast majority (up until ~ Java) of all software on desktops and below were written in C. This also has implications for security as catching things like out of bound access or integer overflow isn't part of C so doing it comes with an explicit cost even when it's cheap in hardware.
afiori 6y ago
Based on other comments: The Javascript spec decided to standardize float operations and (in part) opted for whatever x86 did. ARM had different floating point profiles so ARM processors had to emulate in software intel's operations. Thus ARM decided to simply implement intel's operation as an instruction and called it by the relevant use case.

regularfry 6y ago

With reduced instruction sets, though, the idea is to provide common subparts and make them fast rather than dedicated instructions. While it's not odd to see dedicated instructions in CPUs in general, it's jarring to see if you're familiar with ARM chips from back when they had 25 instructions total.

est31 6y ago
Yeah that's how RISC vs CISC is taught in class, I've heard that same thing. I think it's an outdated paradigm though, if it's not been wrong all along. A CISC chip can still officially support instructions, but deprecate them and implement them very slowly in microcode, as is done with some x86 instructions. And a RISC chip manufacturer might just have used this phrase as a marketing line because designing RISC chips is easier than starting with a monster that has tons of instructions, and they needed some catchy phrase to market their alternative. They then get into the gradual process of making their customers happier one by one by adding special, mostly cold, silicon targeted for special workflows, like in this instance. Ultimately, the instruction set isn't that relevant anyways, what's more relevant is how the microcode can handle speculative execution for common workflows. There's a great podcast/interview from the x86 specification author: https://www.youtube.com/watch?v=Nb2tebYAaOA https://www.youtube.com/watch?v=Nb2tebYAaOA