The patch adds operations to `BlockAndValueMapping` and renames it to `IRMapping`. When operations are cloned, old operations are mapped to the cloned operations. This allows mapping from an operation to a cloned operation. Example:
```
Operation *opWithRegion = ...
Operation *opInsideRegion = &opWithRegion->front().front();
IRMapping map
Operation *newOpWithRegion = opWithRegion->clone(map);
Operation *newOpInsideRegion = map.lookupOrNull(opInsideRegion);
```
Migration instructions:
All includes to `mlir/IR/BlockAndValueMapping.h` should be replaced with `mlir/IR/IRMapping.h`. All uses of `BlockAndValueMapping` need to be renamed to `IRMapping`.
Reviewed By: rriddle, mehdi_amini
Differential Revision: https://reviews.llvm.org/D139665
* A Reducer is a kind of RewritePattern, so it's just the same as
writing graph rewrite.
* ReductionTreePass operates on Operation rather than ModuleOp, so that
* we are able to reduce a nested structure(e.g., module in module) by
* self-nesting.
Reviewed By: jpienaar, rriddle
Differential Revision: https://reviews.llvm.org/D101046
