[LLVMdev] Stack maps no longer experimental in 3.5

[Eric Christopher]

On Sat, Jun 7, 2014 at 6:30 PM, Filip Pizlo <fpizlo at apple.com> wrote:
>
>
> On June 7, 2014 at 1:29:04 PM, Alp Toker (alp at nuanti.com) wrote:
>
>
> On 07/06/2014 18:35, Filip Pizlo wrote:
>> That would work. :-)
>>
>> What about exposing C API a function to query for the presence of an
>> intrinsic?
>
> It seems with hindsight that the "experimental" prefix has turned out to
> be a waste of time.
>
> It's only a waste of time if you think that run-time feature detection is a
> bad idea.  I believe that run-time feature detection is a good idea even if
> we didn't need it in this particular case.
>
>
>
> At least without the prefix there was a good chance this churn could be
> avoided as long as the original review was sound, whereas the prefix has
> necessitated churn.
>
> The intrinsic changed a fair bit since the original review.  Both its
> signature and the stackmap format changed.
>
>
>
> I suggest performing a configure-time check in your build system to
> retain backward/forward compatibility instead of attempting to specify C
> API for instruction introspection(!).
>
> Run-time checks are more robust than configure-time checks.  LLVM is a
> moving target and new intrinsics are added all the time, and it shouldn't be
> necessary to recompile all users of LLVM just to get them to recognize that
> the LLVM to which they got linked has the intrinsic that they already knew
> about.
>

Agreed. Sean's idea might work? If not, then I'm down for coming up
with something.

-eric

> -Filip
>
>
>
>
> Alp.
>
>>
>> -Fil
>>
>>> On Jun 7, 2014, at 3:37 AM, Rafael Espíndola <rafael.espindola at gmail.com>
>>> wrote:
>>>
>>>> On 7 June 2014 00:14, Filip Pizlo <fpizlo at apple.com> wrote:
>>>> The only setback is to ensure that we synchronize the renaming with
>>>> WebKit.
>>>>
>>>> The WebKit->LLVM interface currently avoids revision-lock; you can take
>>>> any
>>>> recent revision of either and build a working browser engine. This is
>>>> mostly
>>>> true even when we change the stack map format because of versioning in
>>>> the
>>>> format. I'd rather keep it that way.
>>>>
>>>> Is there a way to do this with intrinsics? I.e. is there a safe way for
>>>> WebKit to query whether "llvm.patchpoint" is an available intrinsic, and
>>>> then fallback to "llvm.experimental.patchpoint" if it's not available?
>>> Keeping both names during a smallish time window should be sufficient,
>>> no?
>>>
>>> Cheers,
>>> Rafael
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>
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