Dmitry Olshansky:

> An expression attribute? Why turn language into a mess over this tiny problem?
>
> It seems to me that you are considering solutions that add arbitrary amounts of complexity to solve relatively small problems.
>
> ...
> That "just" epithet is remarkable self-destruction.

Please be more gentle toward others. Your attitude is poisonous for creativity, and while I have a thick hide and I can ignore comments like this, similar answers could scare away other people from contributing to the discussions. The lack of tact and basic human kindness is a common problem in technical forum. I sometimes do the same mistake, but we should try to be better. Your good work on the regex module shows you are intelligent and qualified, so I'm sure you can also be better toward others.

Regarding the technical topic, array bound checks are not a tiny problem, and it's not a huge one. D has switches and logic to enable and disable them. The Oracle JavaVM ha a good amount of logic to optimize away array bound checks. Similar logic is visible in other language compilers. Ada language has refined features that allow the compiler to safely remove some bound checks without too much inference work. There are several papers on this topic, like the one I've shown in the first post, that show that several intelligent people have studied this topic extensively. Experimental high-performance numeric languages like X10 and Chapel contain several strategies to avoid array bound checks safely. The experience with both famous bugs and the daily experience in debugging programs shows that out-of-bound array access is a frequent source of some of the worst bugs. There are papers that show a 20-100% improvement in performance coming from disabling array bound checks in programs that use arrays a lot, like most scientific programs. And D language seems fit for some heavy numerical work. D Zen considers quite important both performance and safety, so adding logic to the compiler to remove some more array bounds is a very good way to do both things at once.

Regarding my idea of the @bounded, perhaps it's stupid and useless, but you have to understand that it's just an idea. Most ideas are not even wrong, but sometimes the wrong ones lead to better ideas, that sometimes are useful. This has happened many times even in the D history (like my refused suggestion for the @noheap attribute. Now we have @nogc and I like it a lot, it allows me to understand better what my code is doing). If you criticize too much the people that invent ideas, you will have no future.

Bye,
bearophile

On 2 June 2014 10:24, bearophile via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> deadalnix:
>
>
>> What do GDC or LDC generate for these sample code with optimizations on ?
>
>
> This is not an interesting question because those two programs are meant as parts of larger programs. ldc2 optimizes away both programs to "xorl %eax, %eax".
>
> And I can't test on GDC because GDC compiler crashes on my system since years.
>


Then

1) Get a newer version of GDC
2) Raise bugs - you do this for DMD.  Why not GDC?

Iain Buclaw:

> 1) Get a newer version of GDC
> 2) Raise bugs - you do this for DMD.  Why not GDC?

I don't know what to report, it just crashes, with no error messages.

Bye,
bearophile

On 2 June 2014 12:40, bearophile via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> Iain Buclaw:
>
>
>> 1) Get a newer version of GDC
>> 2) Raise bugs - you do this for DMD.  Why not GDC?
>
>
> I don't know what to report, it just crashes, with no error messages.
>
> Bye,
> bearophile

That doesn't sound right.  Where does it crash?

- Compile-time?  Crashes *always* have backtraces.

- Runtime? Reduce the program down by hand or using dustmite and send bug to the effect of:  Runtime SEGV doing XXX

On 6/2/2014 4:40 AM, bearophile wrote:
> I don't know what to report, it just crashes, with no error messages.

Report the source code you fed to it that caused the crash.

Walter Bright:

> Report the source code you fed to it that caused the crash.

Even hello world crashes.

Bye,
bearophile

On 2 June 2014 17:33, bearophile via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> Walter Bright:
>
>
>> Report the source code you fed to it that caused the crash.
>
>
> Even hello world crashes.
>
> Bye,
> bearophile


Then that is a start.  Post a bug and report clearly what your environment is.

> Please be more gentle toward others. Your attitude is poisonous for creativity, and while I have a thick hide and I can ignore

Yes, please!

Be good to your fellow D coders!

02-Jun-2014 13:46, bearophile пишет:
> Dmitry Olshansky:
>
>> An expression attribute? Why turn language into a mess over this tiny
>> problem?
>>
>> It seems to me that you are considering solutions that add arbitrary
>> amounts of complexity to solve relatively small problems.
>>
>> ...
>> That "just" epithet is remarkable self-destruction.
>
> Please be more gentle toward others. Your attitude is poisonous for
> creativity, and while I have a thick hide and I can ignore comments like
> this, similar answers could scare away other people from contributing to
> the discussions. The lack of tact and basic human kindness is a common
> problem in technical forum. I sometimes do the same mistake, but we
> should try to be better. Your good work on the regex module shows you
> are intelligent and qualified, so I'm sure you can also be better toward
> others.

Yes, I was on the edge. My apologies.
The point that I agree may be lost due to the emotional amplitude was that ideas became that much more interesting by keeping "entities introduced vs problems solved" count as low as possible.

>
> Regarding the technical topic, array bound checks are not a tiny
> problem, and it's not a huge one. D has switches and logic to enable and
> disable them. The Oracle JavaVM ha a good amount of logic to optimize
> away array bound checks. Similar logic is visible in other language
> compilers. Ada language has refined features that allow the compiler to
> safely remove some bound checks without too much inference work. There
> are several papers on this topic, like the one I've shown in the first
> post, that show that several intelligent people have studied this topic
> extensively. Experimental high-performance numeric languages like X10
> and Chapel contain several strategies to avoid array bound checks
> safely. The experience with both famous bugs and the daily experience in
> debugging programs shows that out-of-bound array access is a frequent
> source of some of the worst bugs.

It would be interesting if you could point to a precedent of expression-level attribute used for enforcing that compiler does elide bounds checking or any other features. The fact that bounds checks can be elided as part of optimization is not new.


> There are papers that show a 20-100%
> improvement in performance coming from disabling array bound checks in
> programs that use arrays a lot, like most scientific programs. And D
> language seems fit for some heavy numerical work. D Zen considers quite
> important both performance and safety, so adding logic to the compiler
> to remove some more array bounds is a very good way to do both things at
> once.

No arguing that, the question about implementing the logic mostly boils down to who would be carrying the torch (doing the work on the compiler). Somewhat joking, giving the prologue of your proposal:

> ... But now I am giving increasing importance to compiler logic that optimizes away bound checks safely.

I hoped you'd want to implement it.

The point about extra attributes to enforce this optimization is that it would a very tough sell.

>
> Regarding my idea of the @bounded, perhaps it's stupid and useless, but
> you have to understand that it's just an idea. Most ideas are not even
> wrong, but sometimes the wrong ones lead to better ideas, that sometimes
> are useful. This has happened many times even in the D history (like my
> refused suggestion for the @noheap attribute. Now we have @nogc and I
> like it a lot, it allows me to understand better what my code is doing).

I suspect that most folks arguing for @nogc never heard of @noheap, and that's the problem with generating ideas for the sake of throwing them out there. Ideas as they stand are cheap, it's refined ideas that are priceless. Yes, a weak idea can turn out to be useful, after a lot of work was spent on refining it.

> If you criticize too much the people that invent ideas, you will have no
> future.

It goes both ways. Accepting everything is the definition of disaster.

> Bye,
> bearophile


-- 
Dmitry Olshansky

On Monday, 2 June 2014 at 09:24:38 UTC, bearophile wrote:
> deadalnix:
>
>> What do GDC or LDC generate for these sample code with optimizations on ?
>
> This is not an interesting question because those two programs are meant as parts of larger programs. ldc2 optimizes away both programs to "xorl %eax, %eax".
>
> And I can't test on GDC because GDC compiler crashes on my system since years.
>
> Bye,
> bearophile

I think we should focus on solving problems that modern backend
aren't capable to optimize. If they are able, then we should
focus on other thing, or identify the cases where they are unable
to do so, figure out why, and find a solution (maybe improving
existing optimizers are the road, maybe improving the frontend to
feed more infos to the optimizer is the way to go, maybe
something else...).