[cancerhacker]

It’s fun to consider how C devolves into assembler. In my mind, C and its derivatives dissolve into 68K assembler as I’m writing or debugging. Thinking about code this way lets me get a feel for how all the bits all fit together.

It seems like a lost art to think that way. It’s disturbing to me how many candidates couldn’t write Hello World and compile it from the command line.

Everyone should spend some time with godbolt.org or better, the -save-temps compiler flag, to see how changes affect your generated code. Right now. I’ll wait. (Shakes cane at kids)

[anyfoo]

In the kernel developer world on the other hand, it's still very common to think about how the C code one writes translates into assembly. (Honestly, I think C should not be used much outside developing kernels anyway, and even there it's just legacy, but that's just personal opinion.)

But it's rough, and dangerous. Optimizers do a lot these days, and I really mean a lot. Besides completely mangling your program order, which includes shoving entire blocks of code into places that you might not have guessed, they also do such things as leveraging undefined behavior for optimizations (what the article is partly about), or replacing entire bits of code by function calls. (A compiler might make code out of your memcpy(), and vice versa; the latter can be especially surprising.)

If you care about the assembly representation of your C code (which kernel developers often do), you will spend a lot of time with the "volatile" keyword, compiler barriers, and some obscure "__attribute__"s.

But I agree, even with those caveats in mind, it's a very useful skill to imagine your C code as what it translates to (even if that representation is just a simplified model of what the compiler will actually do).

[fsckboy]

>leveraging undefined behavior for optimizations

that is a poor way to handle UB as it introduces bugs (which are UB themselves). If a compiler detects UB, it should flag an error so the source code gets changed. compilers (or any software really) should never be maliciously compliant.

[unwind]

I kind of share this feeling (I knew 68K assembler before learning C), but having spent ~30 years writing C, publishing some open source software in C, reading comp.lang.c and draft standards, as well as answering many C questions on Stack Overflow back when it was cool, let me tell you: it's not a good model any more (if it ever was). :)

C is specified against an abstract (not virtual) machine, and it matters.

All the talk about how undefined behaviors give the compiler right to shuffle and/or remove code really break the analogy with assembler, where most things become Exactly What You Say.

[lalaithion]

How is this related to the linked article? Assemblers won’t delete your code for treating a register with a float in it like an integer.