[PATCH] D35700: DAGCombiner: Extend reduceBuildVecToTrunc to handle non-zero offset

[Zvi Rackover via Phabricator via llvm-commits]

zvi created this revision.

Adding support for combining power2-strided build_vector's where the
first build_vectori's operand is extracted from a non-zero index.

Example:

v4i32 build_vector((extract_elt V, 1),

  (extract_elt V, 3),
  (extract_elt V, 5),
  (extract_elt V, 7))

-->
 v4i32 truncate (bitcast (shuffle<1,u,3,u,4,u,5,u,6,u,7,u> V, u) to v4i64)


https://reviews.llvm.org/D35700

Files:
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  lib/Target/X86/X86ISelLowering.cpp
  lib/Target/X86/X86ISelLowering.h
  test/CodeGen/X86/shuffle-strided-with-offset-256.ll
  test/CodeGen/X86/shuffle-strided-with-offset-512.ll
  test/CodeGen/X86/vector-shuffle-512-v32.ll

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