Standard way to supply hints to branches

[Manu]

On Tue, 27 Aug 2024 at 15:27, Manu <turkeyman at gmail.com> wrote:

> On Mon, 26 Aug 2024 at 17:16, Walter Bright via Digitalmars-d <
> digitalmars-d at puremagic.com> wrote:
>
>> On 8/24/2024 9:47 AM, Manu wrote:
>> > C++ is way ahead on this... they added attributes to the language years
>> back,
>> > and they defined [[likely]] and [[unlikely]] post-fix on control
>> statements.
>> > It's really convenient, it reads well, and it's easy to retrofit
>> without
>> > disturbing the code.
>> > That's the de-facto now, and we should follow it.
>>
>> It's unattractive.
>>
>> I provided two alternate means to accomplish the same thing elsewhere in
>> this
>> thread.
>>
>>
>> https://www.digitalmars.com/d/archives/digitalmars/D/Standard_way_to_supply_hints_to_branches_375697.html#N375717
>>
>
> "Unattractive"? ... seriously?
> Your suggestions were to quite seriously molest the code, reordering,
> adding extra scopes, inverting logic, nonsense statements like `do {}
> while(0)`, using labels and goto's which doesn't marry well with general
> control flow and RAII type things... sorry; but "unattractive"? That might
> be the most bizarre thing I've ever heard you say! ;)
>

Just so it's clear what's going on here; certain microcontrollers don't
have branch predictors at all; so hinting is essential on these exotic
platforms. Your suggestions could appear in almost every single
at-least-warm function, and it's not clear how they marry with eachother.
We discussed 2 principle cases; likely early return because of short-path
or cached value, and unlikely early return due to argument validation
failure. Plenty of functions contain both cases, and plenty of functions
contain numerous such items.
Try and imagine how your suggestion scales when there are 4-5 conditions
that need to be tested on function entry, and they don't all receive the
same hint. I value readable and maintainable code...
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