[all-commits] [llvm/llvm-project] b6c8fe: [NFC] [PowerPC] Remove dead code in BUILD_VECTOR p...

[Qiu Chaofan via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: b6c8feb29fce39121884f7e08ec6eb0f58da3fb7
      https://github.com/llvm/llvm-project/commit/b6c8feb29fce39121884f7e08ec6eb0f58da3fb7
  Author: Qiu Chaofan <qiucofan at cn.ibm.com>
  Date:   2021-01-05 (Tue, 05 Jan 2021)

  Changed paths:
    M llvm/lib/Target/PowerPC/PPCISelLowering.cpp

  Log Message:
  -----------
  [NFC] [PowerPC] Remove dead code in BUILD_VECTOR peephole

The piece of code tries to use splat+shift to lower build_vector with
repeating bit pattern. And immediate field of vector splat is only 5
bits (-16~15). It iterates over them one by one to find which
shifts/rotates to number in build_vector.

This patch removes code to try matching constant with algebraic
right-shift because that's meaningless - any negative number's algebraic
right-shift won't produce result smaller than itself. Besides, code
(int)((unsigned)i >> j) means logical shift-right in C.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D93937