[PATCH] Extend EarlyCSE to handle basic cases from JumpThreading and CVP

[Philip Reames]

I'll throw it in Local.h/cpp for the moment, but I may go back and write 
the dominated use iterator.  Doing that as a filter on an iterator range 
shouldn't be too challenging.  I definitely want to do that refactor as 
it's own change set though.

I'll update the patch with the commonned functionality in a moment. What 
are you thoughts otherwise?

On 05/13/2015 05:14 PM, Daniel Berlin wrote:
> This is a good question.
>
> I looked through, and i see that it is a common idiom, but often there
> is a small amount of other code people are doing in the middle or as
> part of replacement.  For example,
> Transforms/ObjCARC/ObjCARCContract.cpp:552
>
> If it's not too much to ask, i actually think the best option may be
> something like "a dominated use iterator".
>
> IE
>
> Instead of replaceAllDominatedUses(From, To, DomRoot)
>
> for (auto &Use : dominated_edge_uses(From, DomRoot))
>    {
>        // Do whatever extra stuff they  they want
>       Use.set(To);
>     }
>
>
> and
> instead of
> replaceAllDominatedUses(From, To, From->getParent())
>
> for (auto &Use: dominated_uses(From))
>    Use.set(To);
>
>
> If that's too much, let's just put replaceAllDominatedUses in local.* for now.
>
>
>
>
>
>
>
> On Wed, May 13, 2015 at 4:13 PM, Philip Reames
> <listmail at philipreames.com> wrote:
>> ================
>> Comment at: lib/Transforms/Scalar/EarlyCSE.cpp:490
>> @@ +489,3 @@
>> +                  ToUpdate.push_back(IU);
>> +            for (Instruction *UserI : ToUpdate) {
>> +              DEBUG(dbgs() << "EarlyCSE CVP: Replace dominated use of '"
>> ----------------
>> dberlin wrote:
>>> Can you common this part with GVN's replaceAllDominatedUsesWith?
>>>
>>> (IE just move that function somewhere common and use it?)
>> Absolutely.  Didn't know that existed.  Would it make sense to put that directly on Value?  Or would you rather see it as a helper function in Local.h or someplace similar?
>>
>> http://reviews.llvm.org/D9763
>>
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