[PATCH] [Core] Update references in parallel

Rui Ueyama ruiu at google.com
Fri Mar 20 12:59:46 PDT 2015

On Thu, Mar 19, 2015 at 6:33 PM, Sean Silva <chisophugis at gmail.com> wrote:

> I really don't like this approach. It has large memory contention in the
> inner loop even though this computation doesn't inherently have any. Also
> it is using an extremely cache-unfriendly design, along with putting a
> `new` into the inner loop, causing contention inside the memory allocator
> besides the usual allocation slowness.
> We could just store a bit inside the Atom that marks it as dead. That
> avoids a bunch of hash table lookups in the _deadAtoms map anyway. We have
> a ton of space in the Atom base class in the _definition field, which is
> only using 2 bits of a pointer-aligned field (aligned to the vptr). We
> already have the _definition field loaded (and in cache) due to the
> dyn_cast above (which checks _definition). So it's just an OR and a store
> to mark it: no extra loads, no extra cache misses, no synchronization.

I agree that this would be a better approach than our own concurrent queue.
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