[all-commits] [llvm/llvm-project] b3bd0c: [SystemZ] Eliminate the need to create a zero vect...

[Jonas Paulsson via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: b3bd0c37eced4d149b44eaa9a2700c073927b543
      https://github.com/llvm/llvm-project/commit/b3bd0c37eced4d149b44eaa9a2700c073927b543
  Author: Jonas Paulsson <paulsson at linux.vnet.ibm.com>
  Date:   2020-05-19 (Tue, 19 May 2020)

  Changed paths:
    M llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
    M llvm/test/CodeGen/SystemZ/vec-perm-14.ll

  Log Message:
  -----------
  [SystemZ] Eliminate the need to create a zero vector by reusing the VPERM mask.

Try to avoid creating VGBMs by reusing the permutation mask if it contains a
zero. If the first byte was into (any byte of) a zero vector, then the first
byte of the mask can become zero and reused by putting the mask also as the
first operand. If there instead was a first-byte use of the other source
operand, then that zero index can be reused if the mask is placed as the
second operand.

Review: Ulrich Weigand

Differential Revision: https://reviews.llvm.org/D79925