[Joker_vD]

Nothing justifies the prolonging of C torture either, except of the C's wide spread. Why do you think modern CPUs still expose mostly C-abstract-machine-like interface instead of their actual out-of-order, pipelined, heterogeneous-memory-hierarch-ied internal workings?

[phkahler]

>> Why do you think modern CPUs still expose mostly C-abstract-machine-like interface instead of their actual out-of-order, pipelined, heterogeneous-memory-hierarch-ied internal workings?

Because exposing that would be a huge burden on the compiler writers. Intel tried to move in that direction with Itanium. It's bad enough with every new CPU having a few new instructions and different times, the compiler guys would revolt if they had to care how many virtual registers existed and all the other stuff down there.

But why C? If you want languages to interface with each other it always comes down C as a lowest common denominator. It's even hard to call C++ libraries from a lot of things. Until a new standard down at that level comes into widespread use hardware will be designed to run C code efficiently.

[still_grokking]

> Until a new standard down at that level comes into widespread use hardware will be designed to run C code efficiently.

Exactly this hinders any substantial progress in computer architecture for at least 40 years now.

Any hardware today needs to simulate a PDP-7 more or less… As otherwise the hardware is doomed to be considered "slow" should it not match the C abstract machine (which is mostly a PDP-7) close enough. As there is no alternative hardware available nobody invests in alternative software runtime models. Which makes investing in alternative hardware models again unattractive as no current software could profit from it. Here we're gone full circle.

It's a trap. Especially given that improvements in sequential computing speed are already difficult to achieve and it's known that this will become even more and more difficult in the future, but the computing model of C is inherently sequential and it's quite problematic to make proper use of increasingly more parallel machines.

What we would need to overcome this would be a computer that is build again like the last time many years ago, as a unit of hard and software which is developed hand in hand with each other form the ground up. Maybe this way we could finally overcome the "eternal PDP-7" and move on to some more modern computer architectures (embracing parallelisms in the model from the ground up, for example).

[6510]

I don't have words to describe how exciting that would be. The only way I could see it happen is if the existing legacy architecture would be one (or many) of the parallel processes so that efforts to make it run legacy software don't consume the entire project. I really do think it possible to make a "sane" machine language that doesn't need layers of abstraction or compilers and is easy to learn.

[uticus]

My favorite article on this: "C Is Not a Low-level Language: Your computer is not a fast PDP-11"

Hacker news post: https://news.ycombinator.com/item?id=16967675

and again: https://news.ycombinator.com/item?id=21888096

[failuser]

GPUs are pretty different, despite exposed interface being about the same C

[pjmlp]

It is not the same C, it is a dialect full of extensions, and it only applies to OpenCL, which it was one of the reasons why it failed and forced Khronos to come up with SPIR, playing catch up the polyglot PTX environmnent of CUDA.

OpenCL 3.0 is basically OpenCL 1.2, which is OpenCL before SPIR was introduced.

[phkahler]

>> Especially given that improvements in sequential computing speed are already difficult to achieve and it's known that this will become even more and more difficult in the future...

That's perfect. As performance stop increasing just by shrinking transistors, other options will have a chance to prove themselves.

>> but the computing model of C is inherently sequential and it's quite problematic to make proper use of increasingly more parallel machines.

IMHO Rust will help with that. The code analysis and ownership guarantees should allow the compiler to to decide when things can be run in parallel. Rust also forces you to write code that will be easier to do that. It's not a magic bullet but I think it will raise the bar on what we can expect.

[pjmlp]

> If you want languages to interface with each other it always comes down C as a lowest common denominator

Nope, "always" only applies to OS written in C and usually following POSIX interfaces as they OS ABI.

C isn't the lowest common denominator on Android (JNI is), on Web or ChromeOS (Assembly / JS are), on IBM and Unisys mainframes (language environments are), on Fuchsia (FIDL is), just as a couple of examples.

[atq2119]

CPUs expose a "mostly-C-abstract-machine-like" interface because this allows chip designers to change the internal workings of the processor to improve performance while maintaining compatibility with all of the existing software.

It has nothing to do with C, specifically, but with the fact that vast amounts of important software tend to be distributed in binary form. In a hypothetical world where everybody is using Gentoo, the tradeoffs would be different and CPUs would most likely expose many more micro-architectural details.

[dialamac]

> Why do you think modern CPUs still expose mostly C-abstract-machine-like interface

I don’t think that, because they don’t. Your premise is hogwash.

Modern RISC derived CPUs for the most part expose a load store architecture driven by historical evolution of that micro arch style and if they are SMP a memory model that only recently has C and C++ adapted to with standards. Intels ISA most assuredly was not influenced by C. SIMD isn’t reminiscent of anything standard C either.

Also you might want to look into VLIW and the history of Itanium for an answer to your other question.

[Dylan16807]

> Also you might want to look into VLIW and the history of Itanium for an answer to your other question.

There's only one question. What do you mean?

But Itanium wasn't out of order. How does that even come close to answering a question about exposed out-of-order machinery?

[rvp-x]

There is one CPU that exposes its out of order inner workings, the VIA C3 ("ALTINST"). The unintended effects are so bad that people that accidentally discovered it referred to it as a backdoor: https://en.wikipedia.org/wiki/Alternate_Instruction_Set

[ithkuil]

> [..] referred to it as a backdoor

Because it was implemented in a flawed way.

> "In 2018 Christopher Domas discovered that some Samuel 2 processors came with the Alternate Instruction Set enabled by default and that by executing AIS instructions from user space, it was possible to gain privilege escalation from Ring 3 to Ring 0.["

[wnoise]

It's not like other languages are well-adapted to that either. That's a hard target to code for.

[goatlover]

Why couldn’t Haskell compilers make good use of that?

[jerf]

The "sufficiently smart compiler" [1] has been tried often enough, with poor enough results, that it's not something anyone counts on anymore.

In this case, the most relevant example is probably the failure of the Itanium. Searching for that can be enlightening too, but heres a good start: https://stackoverflow.com/questions/1011760/what-are-the-tec... (For context, the essential Itanium idea was to move complexity out of the chip and into the compiler.)

Also, don't overestimate Haskell's performance. As much fun as I've had with it, I've always been a bit disappointed with its performance. Though for good reasons, it too was designed in the hopes that a Sufficiently Smart Compiler would be able to turn it into something blazingly fast, but it hasn't succeeded any more than anything else. Writing high-performance Haskell is a lot like writing high performance Javascript for a particular JIT... it can be done, but you have to know huge amounts of stuff about how the compiler/JIT will optimize things and have to write in a very particular subset of the language that is much less powerful and convenient than the full language, with little to no compiler assistance, and with even slight mistakes able to trash the perfromance hardcore as some small little thing recursively destroys all the optimizations. It's such a project it's essentially writing in a different language that just happens to integrate nicely with the host.

[1]: https://duckduckgo.com/sufficiently smart compiler

[DavidSJ]

This is reminiscent of my experience designing SQL queries to be run on large MySQL databases.

I had to write my queries in such a way that I was basically specifying the execution plan, even though in theory SQL is practically pure set theory and I shouldn’t have to care about that.

[failuser]

You can stuff Haskell-drived bluespec into FPGA.

[erosenbe0]

Well it turned out that for running scalar code with branches and stack frames exposing too much to the compiler was not helpful, especially as transistor budgets increased. So as long as we program with usual functions and conditionals this is what we have.

I can swap out a cpu for one with better IPC and hardware scheduling in 10 minutes but re-installing binaries, runtime libraries, drivers, firmware to get newly optimized code -- no way. GPU drivers do this a bit and it's no fun.