[PATCH] D119559: [DAGCombine] Basic combines for AVG nodes.

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: RKSimon, craig.topper, spatel, efriedma.
Herald added subscribers: ecnelises, hiraditya.
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This adds very basic combines for AVG nodes, mostly for constant folding and handling degenerate (zero) cases. The code performs mostly same transforms as visitMULHS, adjusted fro AVG nodes.

Constant folding extends to a higher bitwidth and drops the lowest bit. Undef is transformed to 0, as the `add x, undef` could be treated as 0. There is also a transform for `avgfloor x, 0` transforming to `shr x, 1`.


https://reviews.llvm.org/D119559

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/AArch64/hadd-combine.ll

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