[_kst_]

I see a huge semantic gap between assembly language and C.

An assembly language program specifies a sequence of CPU instructions. The mapping between lines of code and generated instructions is one-to-one, or nearly so.

A C program specifies run-time behavior, without regard to what CPU instructions might be used to achieve that.

C is at a lower level than a lot of other languages, but it's not an assembly language.

[vnorilo]

And yet modern assembly does not correspond 1:1 to the micro-ops the CPU runs or even necessarily the order in which they run.

Both ISA-level assembly and C are targeting an abstract machine model, even if the former is somewhat further removed from hardware reality.

[arghwhat]

Java also targets an abstract machine model (JVM) - such statement really doesn't mean much.

Assembly is not about corresponding to exactly which gates open when in the CPU. It's just the human writable form of whatever the CPU ingests, whereas C is an early take on a language reasonable capable of expressing higher level ideas with less low-level noise.

I seriously doubt anyone who has written projects in assembly would make such comparisons...

[vnorilo]

>I seriously doubt anyone who has written projects in assembly would make such comparisons...

With genuine respect, I believe this type of insinuation is rarely productive.

Someone might still have silly opinions, even if they have been paid to write assembly for 8-24-64 bit cisc, risc, ordered and out of order ISAs, and maybe compilers too. Peace :)

[arghwhat]

Yes but someone might also have silly opinions from having no experience how production assembly actually looks, such as underestimating just how different working with that is to working in high-level languages like C and why such languages were quite revolutionary. :)

This should not be mistaken as appeal to authority, it is merely reasonable discrimination between those speaking from experience, and those forming opinions without experience.

If one believes those with experience has poorly informed opinions, they're always free to gain experience and associated perspective. They will then either have the fundamentals to properly push their viewpoint, or end up better understanding and aligning with the common viewpoint.

[cylemons]

Sure but from software POV assembly is the lowest level you can target

[torstenvl]

Which assembly? Assembly with macros? Assembly with synthetic instructions?

If you use

    mov %i0, %l0

instead of

    or %g0, %i0, %l0

Then that isn't "the lowest level you can target."

[cylemons]

I was thinking of x86 when I wrote that, also I am not sure macros count as an abstraction level since they are just preprocessors?

What I meant to say is that since there is no way to directly write microcode, assembly is the lowest level software can target.

[jcelerier]

Yes and no, you can use c in situations where there's no "assembly", for instance when synthesizing FPGAs. You target flow graphs directly in that case IIRC.

[IshKebab]

> And yet modern assembly does not correspond 1:1 to the micro-ops the CPU runs or even necessarily the order in which they run.

Nobody claimed that. It corresponds to the instructions the CPU runs and their observable order.

Also it's really only x86 that uses micro-ops (in the way that you mean), and there are still plenty of in-order CPUs.

[vnorilo]

sure, I was thinking of large OO cores. "Correspondd to the instructions the cpu runs and their observable order" is how I'd characterize C as well, but to each their own.

[flohofwoe]

> And yet modern assembly does not correspond 1:1 to the micro-ops the CPU runs or even necessarily the order in which they run.

It's still much closer to the input machine code compared to what compiler optimizer passes do to your input C code ;)

[vnorilo]

I have empathy for this having written compiler passes for 10ish years of my career. But as I've studied register renaming, speculative branch prediction and trace caches I would no longer agree with your last sentence. It's fine though, totally just an opinion.