force inline/not-inline

[Brandon Ragland via Digitalmars-d]

On Tuesday, 28 July 2015 at 21:30:11 UTC, Jonathan M Davis wrote:
> On Tuesday, 28 July 2015 at 21:24:31 UTC, David Nadlinger wrote:
>> On Tuesday, 28 July 2015 at 15:56:52 UTC, Jonathan M Davis 
>> wrote:
>>> It[Accepting Booleans]'s far more flexible in generic code.
>>
>> It's the other way round. pragma(inline) has currently *three* 
>> behaviors:
>>
>> pragma(inline);
>> pragma(inline, true);
>> pragma(inline, false);
>>
>> There is no way to represent those as a single boolean.
>
> The second two states can be. So, you can turn inlining on and 
> off by feeding it a template argument or the result of a 
> function or something. But it is true that you'd be stuck with 
> a static if in the case that you just wanted to set it to the 
> default behavior. I don't know what you'd do to be able to take 
> an argument for all three though - maybe a string or just some 
> known integral value?
>
> I don't know how much it really matters ultimately though, 
> since I expect that for the most part, the folks who are going 
> to be using this pragma won't be using it generically.
>
> Personally, I very much doubt that I'll ever use it, since I've 
> never worked on code that cared about performance so much that 
> you _had_ to force inlining somewhere. The compiler usually 
> does a good enough job (though that's with C++ compilers; who 
> knows how well dmd does).
>
> - Jonathan M Davis

Even for an application that you would assume does a fine job, if 
you know, via profiling or unittests that a certain expression or 
method takes a bit of time due to excessive calls, it might just 
shave off a noticeable amount of time.

Case in point: live dynamic report generation. Let's say we have 
millions of records from a database and we want to process them 
and churn out a report. If this is done live, this could easily 
take minutes depending on the calculations and manipulations you 
need to do. If a call to a method is made every record, you could 
easily shave off 10-30 seconds with forcing an inline. And 
believe me, 10-30 seconds makes a huge difference when you're 
waiting around for 5+ minutes or more.

There's also time sensitive trading systems that don't want to be 
half a second slow, due to all that money they want now, now , 
now.

You'd be surprised how many places you could save a few seconds 
here or there with a smart inline attribute that the compiler 
might have missed.

It's been my experience that DMD doesn't really do a good job 
with this. GDC is much much better, but DMD truly lacks luster 
with inlining.