[PATCH] D25172: [MSSA] Initial version of avoiding unnecessary use walks when calling getClobberingMemoryAccess

[George Burgess IV via llvm-commits]

> So then isOptimized is "OldDef == Def"?

"OldDef == getDefiningAccess()->getID()", yeah. Pointer equality initially
seems a bit harder to get right, since we could delete a Def and, purely by
chance, later make a new Def at the same address. Though, maybe I'm just
being paranoid. :)

> Oh, it's just more efficient than having a densemap based cache if you
can make it work

SGTM; thanks. Until we get an implementation for Defs, would it be better
to put these methods on `MemoryUse`, then?

On Mon, Oct 3, 2016 at 8:24 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

>
>
> On Mon, Oct 3, 2016 at 5:09 PM, George Burgess IV <
> george.burgess.iv at gmail.com> wrote:
>
>> george.burgess.iv added inline comments.
>>
>>
>> > MemorySSA.cpp:2185
>> > +  // Note: Currently, we do not store the optimized def result because
>> we'd need
>> > +  // a separate field, since we can't use it as the defining access.
>> > +  if (StartingAccess->isOptimized())
>>
>> RE: `Note: ...`: can you bring me through why having this on a Def is
>> would be useful?
>
>
> Oh, it's just more efficient than having a densemap based cache if you can
> make it work :)
>
> It's optimally efficient space wise, but  you may pay the price in
> invalidaion time.
>
> Is the cache just invalidated too aggressively?
>
>
>>
> https://reviews.llvm.org/D25172
>>
>>
>>
>>
>
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