[fpc-devel] Question on updating FPC packages

[J. Gareth Moreton]

Well, when it comes to the specific changes I made to uComplex... the 
compiler might be able to detect a kind of 'auto-const' system, but 
actually inserting 'const' into the formal parameters helps with syntax 
checking as well as generating more efficient code, namely modifying the 
parameter when you're perhaps not supposed to.

For vectorcall, I don't think the compiler will correctly guess when and 
when not to use the calling convention, and there are times where you 
may not want to use vectorcall, usually when interfacing with 
third-party programs or libraries.  In this case, it's more likely that 
the programmer may stumble upon unintented behaviour if it tries to 
enable vectorcall for something that is meant to be the default 
Microsoft ABI instead.

And using assembly language to directly call the uComplex routines I 
don't think is a realistic real-world example, considering that's a 
situation where you're more likely to be using the XMM registers 
directly to do such mathematics.  Besides, I think all bets are off when 
it comes to assembly language - in this instance I tried to make sure 
that Pascal code didn't have to change though (other than a 
recompilation maybe).

I could just say 'screw it' and write my own complex number library, but 
then that would just add to the growing collection of third-party 
libraries instead of a standard set of libraries that are antiquated and 
potentially sluggish on modern systems.

Gareth aka. Kit

On 30/10/2019 22:02, Florian Klämpfl wrote:
> Am 29.10.19 um 14:06 schrieb Marco van de Voort:
>>
>> Op 2019-10-27 om 10:46 schreef Florian Klämpfl:
>>> Am 27.10.19 um 10:27 schrieb Michael Van Canneyt:
>>>> If you genuinely believe that micro-optimization changes can make a 
>>>> difference:
>>>>
>>>> Submit patches. 
>>>
>>> As said: I am against applying them. Why? They clutter code and 
>>> after all, they make assumptions about the current target which not 
>>> might be always valid. And time testing them is much better spent in 
>>> improving the compiler and then all code benefits. Another point: 
>>> for example explicit inline increases normally code size (not always 
>>> but often), so it is against the use of -Os. Applying inline 
>>> manually on umpteen subroutines makes no sense. Better improve auto 
>>> inlining.
>>
>> Auto inlining is also no panacea.   It only works with heuristics, 
>> and is thus only as good as a formula of the heuristic.
>
> Yes. And manually adding inline is only as good as the knowledge of 
> the user doing so. If somebody implements it right (I did not, I used 
> the easiest approach and used an existing function to estimate the 
> complexity of a subroutine). The compiler can just count the number of 
> the generate instructions or even calculate the length of the 
> procedure and then decide to keep the node tree for inlining.
>
>>
>> Changing calling conventions, vectorizing, loops all complicates 
>> that, and it will never be perfect, and a change here will lead to a 
>> problem there etc.
>
> See above.
>
>>
>> If you know a routine can evaluate to one instruction in most cases, 
>> I don't see anything wrong with just marking it as such.
>>
>
> The compiler knows this as well as the compiler generated the code. 
> Why should I guess if the compiler knows?
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