[all-commits] [llvm/llvm-project] cb5612: [DAGCombiner] reduce extract subvector of concat

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: cb5612e2df893728887bedd41aa2293f454c7845
      https://github.com/llvm/llvm-project/commit/cb5612e2df893728887bedd41aa2293f454c7845
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2020-01-09 (Thu, 09 Jan 2020)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/X86/avg.ll
    M llvm/test/CodeGen/X86/pr34657.ll
    M llvm/test/CodeGen/X86/x86-interleaved-access.ll

  Log Message:
  -----------
  [DAGCombiner] reduce extract subvector of concat

If we are extracting a chunk of a vector that's a fraction of an
operand of the concatenated vector operand, we can extract directly
from one of those original operands.

This is another suggestion from PR42024:
https://bugs.llvm.org/show_bug.cgi?id=42024#c2

But I'm not sure yet if it will make any difference on those patterns.
It seems to help a few existing AVX512 tests though.

Differential Revision: https://reviews.llvm.org/D72361