GCC Compiler Tests At A Variety Of Optimization Levels Using Clear Linux

[indepe]

Because Gentoo's developers never provided a mechanism to do anything about it. I would have to step through the system one package at a time and tst each individual dependency for correct behaviour. It's not worth it. But what I do know for absolutely for sure is if I build the whole system with -O3 it results in a bunch of random strange behaviour, that then goes away if I rebuild it with -O2.

I don't understand why that's hard to understand.

That's not hard to understand, it just wasn"t clear to me that your own tests are the best knowledge you have of this matter.

So if there are no bug reports about this (that you know of), it could just be some so-called Heisenbug, and not really a problem with any optimization in O3 itself. And if it is, there is the risk that whatever causes it might be added to O2 in the next compiler release.

[indepe]

there are several modern packages on gentoo that dont compile with -O3

This sounds diiferent than what duby describes. In that case, it sounds like everything compiles, but there are runtime problems. Which, according to anything that has been said so far, could be serious bugs in the packages that just happen to get triggered by different code generations.

What you are saying sounds like you get problems at compilation time. What are they? So you know which packages have problems, since you say they are modern? And what do you mean with "modern"?

[cj.wijtmans]

This sounds diiferent than what duby describes. In that case, it sounds like everything compiles, but there are runtime problems. Which, according to anything that has been said so far, could be serious bugs in the packages that just happen to get triggered by different code generations.

What you are saying sounds like you get problems at compilation time. What are they? So you know which packages have problems, since you say they are modern? And what do you mean with "modern"?

Because its both. You get an unstable system and very few packages just fails to build.

[indepe]

Why do you think experience from multiple people isn't meaningful information? I mean really, if you only choose to believe what you experience and not what others experience and then never try to duplicate the other experiences then very few things will ever be meaningful to you.

My response was to a post which indicated having specific knowledge without saying what it is.

[indepe]

Because its both. You get an unstable system and very few packages just fails to build.

So both of you would be able to tell us why those few packages don't build, and which packages they are, if you wanted to?

[duby229]

My response was to a post which indicated having specific knowledge without saying what it is.

Gentoo is not the only option, but an easy one. Just build a gentoo system for yourself. Choose a desktop profile and install your prefered DE. Install it first compiled with -O2 and then rebuild it with -O3. You can see for yourself. It really is hard to describe. You should try to experience it for yourself.

[indepe]

Gentoo is not the only option, but an easy one. Just build a gentoo system for yourself. Choose a desktop profile and install your prefered DE. Install it first compiled with -O2 and then rebuild it with -O3. You can see for yourself. It really is hard to describe. You should try to experience it for yourself.

I wouldn't be able to blame anyone but myself for whatever happens.

[duby229]

I wouldn't be able to blame anyone but myself for whatever happens.

Blame? What blame? You are asking us to define undefinable behaviour. There is no blame, if you want to experience it for yourself, just try.

[indepe]

Blame? What blame? You are asking us to define undefinable behaviour. There is no blame, if you want to experience it for yourself, just try.

If either of you have build problems, then that is not undefinable behavior.

There is a lot of info one could give about that, and a software engineer would be able, quite easily, to bisect the source code and find the specific code that causes problems. Unless the build problems are different each time, in which case it should be identifiable as a compiler (GCC) problem.

[duby229]

If either of you have build problems, then that is not undefinable behavior.

There is a lot of info one could give about that, and a software engineer would be able, quite easily, to bisect the source code and find the specific code that causes problems. Unless the build problems are different each time, in which case it should be identifiable as a compiler (GCC) problem.

You didn't even try it yet, like I've been urging you to. Right now you are just making an assumption that it is definable. But you've already had at least 2 people in this thread, and you came into this thread with a prior misunderstanding. Maybr it is definable, but I just don't know how. If you really do want to get a grasp on this, then you really do need to try it for yourself. You've already been told how to duplicate the experiences we had. Now you just need to duplicate them and see if you can define this behaviour. Or not.

EDIT: The steps to duplicate is, build a gentoo system with -O3. We don't know how to define it, if you think you do, then please feel free to try. But in the mean time telling folks that -O3 is safe is misleading at the minimum. Whether it's the fault of the compiler or the compiled dependency is irrelevant. If it truly is the fault of compiled dependencies, then that is the bigger problem because there must be many of them. Hopefully it is actually a problem with GCC itself, because that is a single point of failure instead of many.