[Mlir-commits] [mlir] [mlir][transforms] Process RegionBranchOp with empty region (PR #123895)

[Mehdi Amini]

joker-eph wrote:

Regions can't be dynamically added, they are fixed after creation, which is why the convention has been for ops like scf.if to create both regions immediately. Adding a block and a yield is "not free" and in general we avoided consuming extra resources when not needed, hence the convention about empty regions.

`scf.if` isn't the only case, for example a function declaration has an empty region as well. This is even codified in the Parser API somehow with the `parseOptionalRegion()` API which follows the pattern in general of:

```
  auto *body = result.addRegion();
  OptionalParseResult parseResult =
      parser.parseOptionalRegion(*body, ...);
```



https://github.com/llvm/llvm-project/pull/123895