[all-commits] [llvm/llvm-project] 08aa95: [mlir][bufferization]-Replace only one use in Tens...

[Amir Bishara via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 08aa95638713a37407367e0e158df6fb82509725
      https://github.com/llvm/llvm-project/commit/08aa95638713a37407367e0e158df6fb82509725
  Author: Amir Bishara <139038766+amirBish at users.noreply.github.com>
  Date:   2024-12-18 (Wed, 18 Dec 2024)

  Changed paths:
    M mlir/include/mlir/Dialect/Bufferization/IR/BufferizableOpInterface.h
    M mlir/lib/Dialect/Bufferization/IR/BufferizableOpInterface.cpp
    M mlir/lib/Dialect/Bufferization/Transforms/EmptyTensorElimination.cpp
    M mlir/test/Dialect/Bufferization/Transforms/one-shot-bufferize-analysis-empty-tensor-elimination.mlir
    M mlir/test/Dialect/Bufferization/Transforms/one-shot-bufferize-empty-tensor-elimination.mlir

  Log Message:
  -----------
  [mlir][bufferization]-Replace only one use in TensorEmptyElimination (#118958)

In many cases the emptyTensorElimination can not transform or eliminate
the empty tensor which is being inserted into the
`SubsetInsertionOpInterface`.

Two major reasons for that:

1- Failing when trying to find a legal/suitable insertion point for the
`subsetExtract` which is about to replace the empty tensor. However, we
may try to handle this issue by moving the needed values which
responsible on building the `subsetExtract` nearby the empty tensor
(which is about to be eliminated). Thus increasing the probability to
find a legal insertion point.

2-The EmptyTensorElimination transform replaces the tensor.empty's uses
all at once in one apply, rather than replacing only the specific use
which was visited in the use-def chain (when traversing from the
tensor.insert_slice). This scenario of replacing all the uses of the
tensor.empty may lead into additional read effects after bufferization
of the specific subset extract/subview which should not be the case.

Both cases may result in many copies in the coming bufferization which
can not be canonicalized.

The first case can be noticed when having a `tensor.empty` followed by
`SubsetInsertionOpInterface` (or in simple words `tensor.insert_slice`),
which have been lowered from `tensor/tosa.concat`.

The second case can be noticed when having a `tensor.empty`, with many
uses and leading to applying the transformation only once, since the
whole uses have been replaced at once.

The first commit in the PR only adds the lit tests for the cases shown
above (NFC), to emphasize how the transform works, in the coming MRs
will upload a slight changes to handle these case.

The second commit in this PR, we want to replace only the specific use
which was visited in the `use-def` chain (when traversing from the
`tensor.insert_slice`'s source).



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