[all-commits] [llvm/llvm-project] 6c3897: Fix block merging (#96871)

[Giuseppe Rossini via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6c3897d90eda4c39789ac9f4efa51db46734a249
      https://github.com/llvm/llvm-project/commit/6c3897d90eda4c39789ac9f4efa51db46734a249
  Author: Giuseppe Rossini <giuseppe.rossini at amd.com>
  Date:   2024-07-02 (Tue, 02 Jul 2024)

  Changed paths:
    M mlir/lib/Dialect/Bufferization/Transforms/BufferDeallocationSimplification.cpp
    M mlir/lib/Transforms/Utils/RegionUtils.cpp
    M mlir/test/Dialect/Bufferization/Transforms/OwnershipBasedBufferDeallocation/dealloc-branchop-interface.mlir
    M mlir/test/Dialect/Linalg/detensorize_entry_block.mlir
    M mlir/test/Dialect/Linalg/detensorize_if.mlir
    M mlir/test/Dialect/Linalg/detensorize_while.mlir
    M mlir/test/Dialect/Linalg/detensorize_while_impure_cf.mlir
    M mlir/test/Dialect/Linalg/detensorize_while_pure_cf.mlir
    M mlir/test/Transforms/canonicalize-block-merge.mlir
    M mlir/test/Transforms/canonicalize-dce.mlir
    M mlir/test/Transforms/make-isolated-from-above.mlir
    A mlir/test/Transforms/test-canonicalize-merge-large-blocks.mlir

  Log Message:
  -----------
  Fix block merging (#96871)

With this PR I am trying to address:
https://github.com/llvm/llvm-project/issues/63230.

What changed:
- While merging identical blocks, don't add a block argument if it is
"identical" to another block argument. I.e., if the two block arguments
refer to the same `Value`. The operations operands in the block will
point to the argument we already inserted
- After merged the blocks, get rid of "unnecessary" arguments. I.e., if
all the predecessors pass the same block argument, there is no need to
pass it as an argument.
- This last simplification clashed with
`BufferDeallocationSimplification`. The reason, I think, is that the two
simplifications are clashing. I.e., `BufferDeallocationSimplification`
contains an analysis based on the block structure. If we simplify the
block structure (by merging and/or dropping block arguments) the
analysis is invalid . The solution I found is to do a more prudent
simplification when running that pass.

**Note**: many tests are still not passing. But I wanted to submit the
code before changing all the tests (and probably adding a couple), so
that we can agree in principle on the algorithm/design.



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