llvm dev - Mar 2020 - Loop Opt WG Meeting Minutes for March 25, 2020

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Wed, March 25, 2020:
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- Input Dependencies in DDG
  - Input edges are not necessary for semantic correctness but are
    useful for developing profitability heuristics
  - They can cause cycles in the graph or impose ordering
    constraints unnecessarily
  - After considering various alternatives decided to explore
    the following approach:
    - Do not establish input dependence edges, but provide the pair
      of input dependent nodes in a side table in the DDG so that
      interested consumers can look them up.

- Unroll-and-Jam (https://reviews.llvm.org/D76132)
  - Legality checks using dependence info still waiting for review.
  - It may be useful to call a meeting among active participants
    in the code review to discuss issues and reach agreement.

- Dependence Analysis (https://reviews.llvm.org/D75628)
  - Agreed to contact Phillip to seek more advice on potential
    improvements to SCEV and/or dependence analysis.

Bardia Mahjour
Compiler Optimizations
IBM Toronto Software Lab
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