[all-commits] [llvm/llvm-project] cd28da: [LV] Change loops' interleave count computation (#...

[Nilanjana Basu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cd28da390f8b8dedd00f9a2a383ec81e90436841
      https://github.com/llvm/llvm-project/commit/cd28da390f8b8dedd00f9a2a383ec81e90436841
  Author: Nilanjana Basu <n_basu at apple.com>
  Date:   2024-01-04 (Thu, 04 Jan 2024)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/interleave_count_for_estimated_tc.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/interleave_count_for_known_tc.ll
    M llvm/test/Transforms/LoopVectorize/PowerPC/large-loop-rdx.ll
    M llvm/test/Transforms/LoopVectorize/PowerPC/optimal-epilog-vectorization.ll
    M llvm/test/Transforms/LoopVectorize/PowerPC/reg-usage.ll
    M llvm/test/Transforms/LoopVectorize/PowerPC/small-loop-rdx.ll
    M llvm/test/Transforms/LoopVectorize/X86/interleave_short_tc.ll

  Log Message:
  -----------
  [LV] Change loops' interleave count computation (#73766)

[LV] Change loops' interleave count computation

A set of microbenchmarks in llvm-test-suite (https://github.com/llvm/llvm-test-suite/pull/56), when tested on a AArch64 platform, demonstrates that loop interleaving is beneficial when the vector loop runs at least twice or when the epilogue loop trip count (TC) is minimal. Therefore, we choose interleaving count (IC) between TC/VF & TC/2*VF (VF = vectorization factor), such that remainder TC for the epilogue loop is minimum while the IC is maximum in case the remainder TC is same for both.

The initial tests for this change were submitted in PRs:
https://github.com/llvm/llvm-project/pull/70272 and https://github.com/llvm/llvm-project/pull/74689.