4 ms·

I have a "why don’t they just" question: if they're going to rely on compiler intrinsics anyway, why don't they just implement the whole darn thing in the compi

I have a "why don’t they just" question: if they're going to rely on compiler intrinsics anyway, why don't they just implement the whole darn thing in the compiler and do whatever they want there? If you're going to marry your code to the compiler, at least take full advantage of it?

seanhunter 2y ago
I think that’s an excellent suggestion tbh (and could meetmy two criteria as well) and someone may well do that. The thing they want seems perfectly reasonable to me and wouldn’t only benefit the kernel.
starspangled 2y ago
Assuming good faith, they don't do that because they are kernel developers not compiler developers, and they want it to build on the compilers that real systems have at hand. If somebody proposed a new extension and got llvm and gcc to both implement it today, they would still need something to work on old compilers. The oldest GCC supported by Linux is 10 years old nearly.
- dataflow 2y ago
  But for older compilers they already have something that compiles correctly for valid inputs, no? They don't need e.g. the type-safety-check nonsense for that. The newer compilers will still catch mistakes in the usage sites via the intrinsics.
  - starspangled 2y ago
    For today's compilers they have something that compiles very slowly and they want the type safety checks because those are the ones the kernel developers use. That answers the original question doesn't it? If a new compiler extension was proposed and implemented and released in both llvm and gcc, some years after that they could drop support. But there would be no real imperative to drop support early since they will already have developed some code that works okay on those toolchains.
    - dataflow 2y ago
      > For today's compilers they have something that compiles very slowly and they want the type safety checks because those are the ones the kernel developers use. That answers the original question doesn't it No, the point was for today's compilers they could have something that compiles quickly and does everything they want.
      - starspangled 2y ago
        No they couldn't.
        dataflow 2y ago
        > No they couldn't. Elaborate? Why?
        starspangled 2y ago
        I elaborated in my first reply. Today's compilers don't have such a feature.
        dataflow 2y ago
        Nobody said they already do? I was saying they could implement it as an intrinsic.
        starspangled 2y ago
        They couldn't implement it in today's compilers unless they had a time machine. Today's compilers are already built and distributed and are what kernel developers use to compile their code today. I can't understand what you're finding so difficult about this.
        dataflow 2y ago
        > They couldn't implement it in today's compilers unless they had a time machine. Today's compilers are already built and distributed and are what kernel developers use to compile their code today. I can't understand what you're finding so difficult about this. I am saying they could have either implemented this in the past (and thus had it land by now) or implement it now (and have it land in e.g. GCC in the near future). Neither appears to be the case. I was not suggesting they have a time machine. I can't understand what you're finding so difficult about this.

seanhunter 2y ago

I think that’s an excellent suggestion tbh (and could meetmy two criteria as well) and someone may well do that. The thing they want seems perfectly reasonable to me and wouldn’t only benefit the kernel.

starspangled 2y ago

Assuming good faith, they don't do that because they are kernel developers not compiler developers, and they want it to build on the compilers that real systems have at hand. If somebody proposed a new extension and got llvm and gcc to both implement it today, they would still need something to work on old compilers. The oldest GCC supported by Linux is 10 years old nearly.

dataflow 2y ago
But for older compilers they already have something that compiles correctly for valid inputs, no? They don't need e.g. the type-safety-check nonsense for that. The newer compilers will still catch mistakes in the usage sites via the intrinsics.
- starspangled 2y ago
  For today's compilers they have something that compiles very slowly and they want the type safety checks because those are the ones the kernel developers use. That answers the original question doesn't it? If a new compiler extension was proposed and implemented and released in both llvm and gcc, some years after that they could drop support. But there would be no real imperative to drop support early since they will already have developed some code that works okay on those toolchains.
  - dataflow 2y ago
    > For today's compilers they have something that compiles very slowly and they want the type safety checks because those are the ones the kernel developers use. That answers the original question doesn't it No, the point was for today's compilers they could have something that compiles quickly and does everything they want.
    - starspangled 2y ago
      No they couldn't.
      - dataflow 2y ago
        > No they couldn't. Elaborate? Why?
        starspangled 2y ago
        I elaborated in my first reply. Today's compilers don't have such a feature.
        dataflow 2y ago
        Nobody said they already do? I was saying they could implement it as an intrinsic.
        starspangled 2y ago
        They couldn't implement it in today's compilers unless they had a time machine. Today's compilers are already built and distributed and are what kernel developers use to compile their code today. I can't understand what you're finding so difficult about this.
        dataflow 2y ago
        > They couldn't implement it in today's compilers unless they had a time machine. Today's compilers are already built and distributed and are what kernel developers use to compile their code today. I can't understand what you're finding so difficult about this. I am saying they could have either implemented this in the past (and thus had it land by now) or implement it now (and have it land in e.g. GCC in the near future). Neither appears to be the case. I was not suggesting they have a time machine. I can't understand what you're finding so difficult about this.