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

[Daniel Berlin]

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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