[mlir][bufferization] Add `BufferViewFlowOpInterface` (#78718) This commit adds the `BufferViewFlowOpInterface` to the bufferization dialect. This interface can be implemented by ops that operate on buffers to indicate that a buffer op result and/or region entry block argument may be the same buffer as a buffer operand (or a view thereof). This interface is queried by the `BufferViewFlowAnalysis`. The new interface has two interface methods: * `populateDependencies`: Implementations use the provided callback to declare dependencies between operands and op results/region entry block arguments. E.g., for `%r = arith.select %c, %m1, %m2 : memref<5xf32>`, the interface implementation should declare two dependencies: %m1 -> %r and %m2 -> %r. * `mayBeTerminalBuffer`: An SSA value is a terminal buffer if the buffer view flow analysis stops at the specified value. E.g., because the value is a newly allocated buffer or because no further information is available about the origin of the buffer. Ops that implement the `RegionBranchOpInterface` or `BranchOpInterface` do not have to implement the `BufferViewFlowOpInterface`. The buffer dependencies can be inferred from those two interfaces. This commit makes the `BufferViewFlowAnalysis` more accurate. For unknown ops, it conservatively used to declare all combinations of operands and op results/region entry block arguments as dependencies (false positives). This is no longer the case. While the analysis is still a "maybe" analysis with false positives (e.g., when analyzing ops such as `arith.select` or `scf.if` where the taken branch is not known at compile time), results and region entry block arguments of unknown ops are now marked as terminal buffers. This commit addresses a TODO in `BufferViewFlowAnalysis.cpp`: ``` // TODO: We should have an op interface instead of a hard-coded list of // interfaces/ops. ``` It is no longer needed to hard-code ops.
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