llvm dev - Jul 2016 - RFC: Strong GC References in LLVM

>     Hi all,
>
>
>        2. Introduce a flag on load and stores that either
>             a. Denotes a "gc_safety" control dependence.
>             b. Denotes a "blackbox_safety" control dependence. 
In this case
>                we will probably have some optional metadata on loads and
>                stores to indicate that the control dependence is actually
on
>                GC safety.
>
>
> Suggested name for 2b: "unsafe" or "predicated".
Essentially, that the
> load is not generally safe to do even if the *memory* is generally safe
> to load from because of some external effect.

Sounds like "volatile" to me ...

--Peter Lawrence.
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Hi Peter,

On Mon, Jul 18, 2016 at 6:13 PM, Lawrence, Peter via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>> Suggested name for 2b: "unsafe" or "predicated".
Essentially, that the
>
>> load is not generally safe to do even if the *memory* is generally safe
>
>> to load from because of some external effect.
>
> Sounds like “volatile” to me …
volatile accesses can't be sunk (i.e. changed to execute in a subset
of the cases it would have executed in the original program) or elided
(e.g. if the result of the load is unused), but both of these are
valid for gc references.

-- Sanjoy

> >
> > Sounds like “volatile” to me …
> volatile accesses can't be sunk (i.e. changed to execute in a subset of
the cases it would have executed in the original > > program) or elided
(e.g. if the result of the load is unused), but both of these are valid for gc
references.
> -- Sanjoy
Sanjoy,
             Thanks.  So it sounds "volatile"-ish, is it conceptually
possible to spell out its
semantics in detail ?   if so then it might sound like a (yet another) attribute
"like" volatile.

IE basically I'm agreeing with #2, and you don't need to spell it out in
detail just
for my sake, I'm really asking "can it be spelled out in detail"
when it comes to
documenting the IR, such that someone writing an optimization pass will be able
to do the right thing.
 
--Peter.