[LLVMdev] Loads moving across barriers

Matt Arsenault
2013-12-04T23:33:25Z

On 11/11/2013 03:13 PM, Andrew Trick wrote:
> On Nov 9, 2013, at 1:39 PM, Matt Arsenault <arsenm2 at gmail.com>
wrote:
>
>> On Nov 9, 2013, at 3:14 AM, Chandler Carruth <chandlerc at
google.com> wrote:
>>
>>> Perhaps you're instead trying to say that with certain address
spaces "noalias" (and by inference, "restrict" at the
language level) has a different semantic model than other address spaces? While
it's less worrisome than the first interpretation, I still don't really
like it.
>>>
>> This sounds right. With the constant address space, anything you do is
OK since it’s constant. Private address space is supposed to be totally
inaccessible from other workitems, so parallel modifications aren’t a concern.
The others require explicit synchronization which noalias would need to be aware
of.
> FWIW, it seems generally useful to me to have a nomemfence function
attribute and intrinsic property. We should avoid memory optimization (and
possibly other optimization) across these regardless of alias analysis.
>
I'm think I'll try implementing this. Ideally it would be parameterized
over the address space, so it makes more sense for it to be a memfence
attribute rather than a nomemfence. You would then have an arbitrary