[PATCH] D56784: [X86][SSE] Use PSLLDQ/PSRLDQ to mask out zeroable ends of a shuffle

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: craig.topper, lebedev.ri, spatel, andreadb.

As suggested on PR40318, this patch uses PSLLDQ/PSRLDQ to lower shuffles to zero out the ends of a vector, leaving a sequential inner section.

For pre-SSSE3 we do this for shuffles with zeros at either end (requiring up to 3 shifts), but once PSHUFB is available I've limited this to shuffles with a single zeroable end (2 shifts).


Repository:
  rL LLVM

https://reviews.llvm.org/D56784

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/buildvec-extract.ll
  test/CodeGen/X86/vector-shuffle-128-v16.ll
  test/CodeGen/X86/vector-shuffle-128-v8.ll
  test/CodeGen/X86/vector-shuffle-sse4a.ll

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