[all-commits] [llvm/llvm-project] cdec72: [LoopInterchange] Improve profitability check for ...

[Ryotaro Kasuga via All-commits]

  Branch: refs/heads/users/kasuga-fj/loop-interchange-improve-profitable-vectorization
  Home:   https://github.com/llvm/llvm-project
  Commit: cdec72a2b2c365e29cbe05f2ad2d21b403104999
      https://github.com/llvm/llvm-project/commit/cdec72a2b2c365e29cbe05f2ad2d21b403104999
  Author: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
  Date:   2025-03-27 (Thu, 27 Mar 2025)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopInterchange.cpp
    M llvm/test/Transforms/LoopInterchange/profitability-vectorization-heuristic.ll

  Log Message:
  -----------
  [LoopInterchange] Improve profitability check for vectorization

The vectorization profitability has a process to check whether a given
loop can be vectorized or not. Since the process is conservative, a loop
that can be vectorized may be deemed not to be possible. This can
trigger unnecessary exchanges.
This patch improves the profitability decision by mitigating such
misjudgments. Before this patch, we considered a loop to be vectorizable
only when there are no loop carried dependencies with the IV of the
loop. However, a loop carried dependency doesn't prevent vectorization
if the distance is positive. This patch makes the vectorization check
more accurate by allowing a loop with the positive dependency. Note that
it is difficult to make a complete decision whether a loop can be
vectorized or not. To achieve this, we must check the vector width and
the distance of dependency.



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