[PATCH] D54271: [x86] use shuffles for scalar insertion into high elements of a constant vector

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: RKSimon, craig.topper.
Herald added a subscriber: mcrosier.

As discussed in https://reviews.llvm.org/D54073, we have a potential regression from more aggressive vector narrowing here, so let's try to avoid that by changing build-vector lowering slightly.

Insert-vector-element lowering always does this since there's no "pinsr" for ymm/zmm:

  // If the vector is wider than 128 bits, extract the 128-bit subvector, insert
  // into that, and then insert the subvector back into the result.

...but we can sometimes do better for insert-into-constant-vector by using shuffle lowering.


https://reviews.llvm.org/D54271

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/insert-into-constant-vector.ll

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