[PATCH] D156645: [DAGCombiner] Don't reduce BUILD_VECTOR to BITCAST before LegalizeTypes if VT is legal.

[Jim Lin via Phabricator via llvm-commits]

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Targets may lose some optimization opprtunities for certain vector operation
if we reduce BUILD_VECTOR to BITCAST early.

If VT is not legal, reduce BUILD_VECTOR to BITCAST before LegailizeTypes
can get benefit. Because type-legalizer often scalarizes illegal type of vectors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D156645

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-vslide1down.ll
  llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-vslide1up.ll

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