[all-commits] [llvm/llvm-project] 483544: [mlir][dataflow] Remove Abstract{Sparse, Dense}Latt...

[Zhixun Tan via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4835441d02c19e1c906d6c510c3e35f41d910fe7
      https://github.com/llvm/llvm-project/commit/4835441d02c19e1c906d6c510c3e35f41d910fe7
  Author: Zhixun Tan <phisiart at gmail.com>
  Date:   2022-08-15 (Mon, 15 Aug 2022)

  Changed paths:
    M mlir/include/mlir/Analysis/DataFlow/DenseAnalysis.h
    M mlir/include/mlir/Analysis/DataFlow/SparseAnalysis.h
    M mlir/lib/Analysis/DataFlow/DenseAnalysis.cpp
    M mlir/lib/Analysis/DataFlow/SparseAnalysis.cpp
    M mlir/test/lib/Analysis/DataFlow/TestDenseDataFlowAnalysis.cpp

  Log Message:
  -----------
  [mlir][dataflow] Remove Abstract{Sparse,Dense}Lattice::isAtFixpoint() and an ineffective optimization to simplify public API

Currently, in the MLIR `{Sparse,Dense}DataFlowAnalysis` API, there is a small optimization:

Before running a transfer function, if the "out state" is already at the pessimistic fixpoint (bottom lattice value), then we know that it cannot possibly be changed, therefore we can skip the transfer function.

I benchmarked and found that this optimization is ineffective, so we can remove it and simplify `{Sparse,Dense}DataFlowAnalysis`. In a subsequent patch, I plan to change/remove the concept of the pessimistic fixpoint so that the API is further simplified.

Benchmark: I ran the following tests 5 times (after 3 warmup runs), and timed the `initializeAndRun()` function.

| Test | Before (us) | After (us) |
| mlir-opt -test-dead-code-analysis mlir/test/Analysis/DataFlow/test-dead-code-analysis.mlir | 181.2536 | 187.7074 |
| mlir-opt -- -test-dead-code-analysis mlir/test/Analysis/DataFlow/test-last-modified-callgraph.mlir | 109.5504 | 105.0654 |
| mlir-opt -- -test-dead-code-analysis mlir/test/Analysis/DataFlow/test-last-modified.mlir | 333.3646 | 322.4224 |
| mlir-opt -- -allow-unregistered-dialect -sccp mlir/test/Analysis/DataFlow/test-combined-sccp.mlir | 1027.1492 | 1081.818 |

Note: `test-combined-sccp.mlir` is crafted by combining `mlir/test/Transforms/sccp.mlir`, `mlir/test/Transforms/sccp-structured.mlir` and `mlir/test/Transforms/sccp-callgraph.mlir`.

Reviewed By: aartbik, Mogball

Differential Revision: https://reviews.llvm.org/D131660