[all-commits] [llvm/llvm-project] 9eb8e7: [MLIR][PDL] Clear up the terminology in the root o...
Stanislav Funiak via All-commits
all-commits at lists.llvm.org
Wed Dec 22 11:10:40 PST 2021
Author: Stanislav Funiak <stano at cerebras.net>
Date: 2021-12-22 (Wed, 22 Dec 2021)
[MLIR][PDL] Clear up the terminology in the root ordering graph.
Previously, we defined a struct named `RootOrderingCost`, which stored the cost (a pair consisting of the depth of the connector and a tie breaking ID), as well as the connector itself. This created some confusion, because we would sometimes write, e.g., `cost.cost.first` (the first `cost` referring to the struct, the second one referring to the `cost` field, and `first` referring to the depth). In order to address this confusion, here we rename `RootOrderingCost` to `RootOrderingEntry` (keeping the fields and their names as-is).
This clarification exposed non-determinism in the optimal branching algorithm. When choosing the best local parent, we were previuosly only considering its depth (`cost.first`) and not the tie-breaking ID (`cost.second`). This led to non-deterministic choice of the parent when multiple potential parents had the same depth. The solution is to compare both the depth and the tie-breaking ID.
Testing: Rely on existing unit tests. Non-detgerminism is hard to unit-test.
Reviewed By: rriddle, Mogball
Differential Revision: https://reviews.llvm.org/D116079
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