[PATCH] D20474: when calculating RegUsages, ignore instructions which are uniformed after vectorization

[Wei Mi via llvm-commits]

wmi added inline comments.

================
Comment at: lib/Transforms/Vectorize/LoopVectorize.cpp:4919
@@ -4906,1 +4918,3 @@
+  // Also add all consecutive pointer values and all nonconsecutive pointer
+  // values if gather/scatter is not supported; these values will be uniform
   // after vectorization (and subsequent cleanup) and, until revectorization is
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mkuper wrote:
> Are you sure about this?
> 
> Nonconsecutive pointer values when there is no gather/scatter will be scalarized, but they aren't uniform. 
> So I'm not sure we should be counting them as uniform. This will work correctly for your new use of isUniformAfterVectorization() (since we really don't need vector registers in either case). But I think it may do the wrong thing for the existing use, in getInstructionCost(). We shouldn't be evaluating the cost of non-consecutive loads/stores as if they are a single scalar load/store.
> 
> Am I confused?
Ah, you are right. I misunderstood what uniform means here. Will fix it. 


Repository:
  rL LLVM

http://reviews.llvm.org/D20474