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Comment by ndesaulniers | Hacker News Reader

Some people care more about compile times than the performance of generated code. Perhaps even the correctness of generated code. Perhaps more so than determinism of the generated code. Different people in different contexts can have different priorities. Trying to make everyone happy can sometimes lead to making no one happy. Thus dichotomies like `-O2` vs `-Os`.

EDIT (since HN is preventing me from responding):

> Some people care more about compiler speed than the correctness?

Yeah, I think plenty of people writing code in languages that have concepts like Undefined Behavior technically don't really care as much about correctness as they may claim otherwise, as it's pretty hard to write large volumes of code without indirectly relying on UB somewhere. What is correct in such case was left up to interpretation of the implementer by ISO WG14.

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Some people care more about compiler speed than the correctness? I would love to meet these imaginary people that are fine with a compiler that is straight up broken. Emitting working code is the baseline, not some preference slider.

Let's pretend, for just a second, that the people who do, having been able to learn how to program, are not absolute fucking morons. Straight up broken is obviously not useful, so maybe the conclusions you've jumped to could use some reexamination.

You might have not run Gentoo. Most Gentooers will begrudgingly but eventually admit to cooking their own gonads when updating a laptop.

Anyway, please define: "correctness".

> I would love to meet these imaginary people that are fine with a compiler that is straight up broken.

That's not what I said; you're attacking a strawman.

My point was more so that some people prefer the madness that is -funsafe-math-optimizations, or happen to rely on UB (intentionally or otherwise). What even is "correct" in the presence of UB? What is correct in such case was left up to interpretation of the implementer by ISO WG14.

a compiler introducing bugs into code it compiles is a nightmare thankfully few have faced. The only thing worse would be a CPU bug like the legendary Pentium bug. Imagine you compile something like Postgres only to have it crash in some unpredictable way. How long do you stare at Postgres source before suspecting the compiler? What if this compiler was used to compile code in software running all over cloud stacks? Bugs in compilers are very bad news, they have to be correct.

Yeah, my current boss spent time weeding out such hardware bugs: https://arxiv.org/abs/2110.11519 (EDIT: maybe https://x.com/Tesla_AI/status/1930686196201714027 is a more relevant citation)

They found a bimodal distribution in failures over the lifetime of chips. Infant mortality was well understood. Silicon aging over time was much less well understood, and I still find surprising.

> a compiler introducing bugs into code it compiles is a nightmare thankfully few have faced

Is this true? It’s not an everyday thing, but when using less common flags, or code structures, or targets… every few years I run into a codegen issue. It’s hard to imagine going through a career without a handful…

It's not that uncommon if you work in massive lowish level systems. Clang/LLVM being relatively bug free is the result of many corporate big tech low level compiler swes working with the application swes to debug why XYZ isn't working properly and then writing the appropriate fix. But compiler bugs still come up every so often, I've seen it on multiple occasions.

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