[all-commits] [llvm/llvm-project] d0ea28: [mlir][Transforms] Dialect conversion: Align handl...

[Matthias Springer via All-commits]

  Branch: refs/heads/users/matthias-springer/replace_op_source_mat
  Home:   https://github.com/llvm/llvm-project
  Commit: d0ea28ccd074530154053dcbb64d118290c640ca
      https://github.com/llvm/llvm-project/commit/d0ea28ccd074530154053dcbb64d118290c640ca
  Author: Matthias Springer <mspringer at nvidia.com>
  Date:   2024-08-30 (Fri, 30 Aug 2024)

  Changed paths:
    M mlir/lib/Transforms/Utils/DialectConversion.cpp
    M mlir/test/Transforms/test-legalize-erased-op-with-uses.mlir

  Log Message:
  -----------
  [mlir][Transforms] Dialect conversion: Align handling of dropped values

Handle dropped block arguments and dropped op results in the same way: build a source materialization (that may fold away if unused). This simplifies the code base a bit and makes it possible to merge `legalizeConvertedArgumentTypes` and `legalizeConvertedOpResultTypes` in a future commit. These two functions are almost doing the same thing now.

This commit also fixes a bug where circular materializations were built, e.g.:
```
%0 = "builtin.unrealized_conversion_cast"(%1) : (!a) -> !b
%1 = "builtin.unrealized_conversion_cast"(%0) : (!b) -> !a
// No further uses of %0, %1.
```

This happened when:
1. An op was erased. (No replacement values provided.)
2. A conversion pattern for another op builds a replacement value (first cast op) during `remapValues`, but that SSA value is not used during the pattern application.
3. During the finalization phase, `legalizeConvertedOpResultTypes` thinks that the erased op is alive because of the cast op that was built in Step 2. It builds a cast from that replacement value to the original type.
4. During the commit phase, all uses of the original op are repalced with the casted value produced in Step 3. We have generated circular IR.



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