[PATCH] D151029: [DAG] Combine insert(shuffle(load), load, 0) into a single load

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
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Given an insert of a scalar load into a vector shuffle with mask `u,0,1,2,3,4,5,6` or `1,2,3,4,5,6,7,u` (depending on the insert index), it can be more profitable to convert to a single load and avoid the shuffles. This adds a DAG combine for it, providing the new load is still fast.


https://reviews.llvm.org/D151029

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/insertshuffleload.ll
  llvm/test/CodeGen/Thumb2/mve-insertshuffleload.ll

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