[PATCH][DAGCombiner] Split up an indexed load if only the base pointer value is live

[Adam Nemet]

Ping.

+          for (SDNode *U : N->uses())
+            AddToWorkList(U);

For the review, please consider this written as: AddUsersToWorkList(N)

On Apr 24, 2014, at 5:09 PM, Adam Nemet <anemet at apple.com> wrote:

> Right now the load may not get DCE'd because of the side-effect of updating
> the base pointer.
> 
> This can happen if we lower a read-modify-write of an illegal larger type
> (e.g. i48) such that the modification only affects one of the subparts (the
> lower i32 part but not the higher i16 part).  See the testcase.
> 
> In order to spot the dead load we need to revisit it when SimplifyDemandedBits
> decided that the value of the load is masked off.  This is the
> CommitTargetLoweringOpt piece.
> 
> I checked compile time with ARM64 by sending SPEC bitcode files through llc.
> No measurable change.
> 
> Fixes <rdar://problem/16031651>
> 
> Adam
> 
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