[PATCH] D73892: [SelectionDAG] Optimize build_vector of truncates and shifts

[Sebastian Neubauer via Phabricator via llvm-commits]

sebastian-ne created this revision.
sebastian-ne added a reviewer: bogner.
Herald added subscribers: llvm-commits, kerbowa, hiraditya, jvesely.
Herald added a project: LLVM.

Add a simplification to fuse a manual vector extract with shifts and
truncate into a bitcast.

Unpacking and packing values into vectors is only optimized with
extractelement instructions, not when manually unpacked using shifts
and truncates.
This patch simplifies shifts and truncates into a bitcast if possible.

Simplify (build_vec (trunc $1)

  (trunc (srl $1 width))
  (trunc (srl $1 (2 * width))) ...)

to (bitcast $1)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73892

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AMDGPU/scalar_to_vector.ll
  llvm/test/CodeGen/AMDGPU/vector_shuffle.packed.ll

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