[all-commits] [llvm/llvm-project] 5d281a: [LoopInterchange] Constrain number of load/stores...

[Madhur Amilkanthwar via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5d281a480e5caae09962b863960d7d057e908a3c
      https://github.com/llvm/llvm-project/commit/5d281a480e5caae09962b863960d7d057e908a3c
  Author: Madhur Amilkanthwar <madhura at nvidia.com>
  Date:   2025-01-21 (Tue, 21 Jan 2025)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopInterchange.cpp
    A llvm/test/Transforms/LoopInterchange/many-load-stores.ll

  Log Message:
  -----------
  [LoopInterchange] Constrain number of  load/stores in a loop (#118973)

In the current state of the code, the transform computes entries for the
dependency matrix until `MaxMemInstrCount` which is 100. After 99th
entry, it terminates and thus overall wastes compile-time.

It would be nice if we can compute total number of entries upfront and
early exit if the number of entries > 100. However, computing the number
of entries is not always possible as it depends on two factors:
1. Number of load-store pairs in a loop.
2. Number of common loop levels for each of the pair.

This patch constrains the whole computation on the number of loads and
stores instructions in the loop.

In another approach, I experimented with computing 1 and constraining
the number of pairs, but that did not lead to any additional benefit in
terms of compile time. However, when other issues are fixed, I can
revisit this approach.



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