[all-commits] [llvm/llvm-project] 294877: [LoopInterchange] Defer CacheCost calculation unti...

[Ryotaro Kasuga via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 29487759e3cc8fc056a599a38b3a6d2d8849a20e
      https://github.com/llvm/llvm-project/commit/29487759e3cc8fc056a599a38b3a6d2d8849a20e
  Author: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
  Date:   2025-07-08 (Tue, 08 Jul 2025)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopInterchange.cpp
    A llvm/test/Transforms/LoopInterchange/delay-cachecost-calculation.ll

  Log Message:
  -----------
  [LoopInterchange] Defer CacheCost calculation until needed (#146874)

LoopInterchange currently stop and exit its process when the number of
loads/stores in the loop is greater than `MaxMemInstrCount`. This
prevents excessive querying to DependenceAnalysis. However, computing
`CacheCost` also involves DependenceAnalysis queries, and their number
can grow to `O(N^2)` in the worst case, where `N` is the number of
loads/stores in the loop. Therefore, we should also avoid calculating it
if the loads/stores count exceeds `MaxMemInstrCount`.
This patch defers the calculation of `CacheCost` until it is actually
needed to reduce compile time. This avoids computing `CacheCost` when
the number of loads/stores is large. Additionally, since this patch
delays its calculation as much as possible, it is also effective in
other scenarios, e.g., when there are no legal loop pairs to exchange.



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