j at j.nl
Sat Apr 4 12:03:46 UTC 2020
On Friday, 3 April 2020 at 20:06:50 UTC, Steven Schveighoffer
> On 4/3/20 3:13 PM, Johan wrote:
>> On Thursday, 2 April 2020 at 12:41:28 UTC, Steven
>> Schveighoffer wrote:
>>> Hm... I thought there was precedent for providing fallback
>>> implementations for intrinsics. That is, you define the
>>> function, which is only used if the intrinsic is not
>>> I can't remember where I saw this. But you could try this by
>>> simply implementing the bitops in core.bitop, and see if they
>>> are used outside ctfe.
>> There are a bunch of functions implemented with `if
>> (!__ctfe)`. DMD and LDC are smart enough to elide
>> `if(false/true)` control flow completely even in debug code,
>> so there is no penalty to using `if (!__ctfe)`.
>> See for example:
> I'm trying to understand that. It looks like you are calling
> the intrinsic that llvm recognizes. What can you do when bsf
> *is* the intrinsic? Does DMD have to change its intrinsic to
> something that's not core.bitop.bsf so we can call it? Or would
> that code as written work if ported to druntime mainline?
I think it'd work without any changes needed. (note the version
> I.e. the compiler replaces the bsf with the intrinsic and
> ignores the implementation in runtime code, but works at
> comiple time.
I think that's correct, yes.
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