[all-commits] [llvm/llvm-project] b3d0c7: [DAGCombiner] avoid narrowing fake fneg vector op

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: b3d0c798367d1dbf07d0357260b432571bff5c7d
      https://github.com/llvm/llvm-project/commit/b3d0c798367d1dbf07d0357260b432571bff5c7d
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2020-02-26 (Wed, 26 Feb 2020)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AArch64/arm64-fp.ll

  Log Message:
  -----------
  [DAGCombiner] avoid narrowing fake fneg vector op

This may inhibit vector narrowing in general, but there's
already an inconsistency in the way that we deal with this
pattern as shown by the test diff.

We may want to add a dedicated function for narrowing fneg.
It's often folded into some other op, so moving it away from
other math ops may cause regressions that we would not see
for normal binops.

See D73978 for more details.