[all-commits] [llvm/llvm-project] 840450: [LV] Clamp MaxVF to power of 2.

[azaks via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 840450549c9199150cbdee29acef756c19660ca1
      https://github.com/llvm/llvm-project/commit/840450549c9199150cbdee29acef756c19660ca1
  Author: Ayal Zaks <ayal.zaks at intel.com>
  Date:   2020-05-25 (Mon, 25 May 2020)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    A llvm/test/Transforms/LoopVectorize/memdep-fold-tail.ll

  Log Message:
  -----------
  [LV] Clamp MaxVF to power of 2.

If a loop has a constant trip count known to be a multiple of MaxVF (times user
UF), LV infers that no tail will be generated for any chosen VF. This relies on
the chosen VF's being powers of 2 bound by MaxVF, and assumes MaxVF is a power
of 2. Make sure the latter holds, in particular when MaxVF is set by a memory
dependence distance which may not be a power of 2.

Differential Revision: https://reviews.llvm.org/D80491