[4Walter&Andrei] D is 40 times slower. We need a new language feature!

[John Colvin via Digitalmars-d]

On Saturday, 20 May 2017 at 11:34:55 UTC, 9il wrote:
> On Saturday, 20 May 2017 at 11:30:54 UTC, John Colvin wrote:
>> On Saturday, 20 May 2017 at 03:24:41 UTC, 9il wrote:
>>> Hello,
>>>
>>> When users write math code, they expect [2, 3, 4] that the 
>>> code like
>>>
>>> [...]
>>
>> What you are saying is that there is a specific shortcoming 
>> that you are observing in optimisers, yes? Perhaps we should 
>> investigate how to fix the optimisers first before insisting 
>> on language additions / changes.
>>
>> Have you talked to someone with experience writing optimisers 
>> about what stops the relevant optimisation being done after 
>> inlining?
>
> I just found that new LLVM solves this issue (and was very 
> surprised).
> The reason that ndslice <=v0.6.1 was so slow is LDC Issue 2121.
> I have added workaround in [2], it is v0.6.2.
>
> [1] https://github.com/ldc-developers/ldc/issues/2121
> [2] https://github.com/libmir/mir-algorithm/pull/41

What's​ surprising about it? Thinking very simplistically (I 
don't know how it actually works), if inlining happened first 
then surely the later optimisation stages wouldn't have a problem 
detecting the necessary loop invariants and hoisting them out.