[flang-commits] [flang] [mlir] [mlir][CSE] Introduce hoist-pure-ops logic to CSE pass (PR #180556)

[Mehdi Amini via flang-commits]

joker-eph wrote:

I've been trying to understand more of the behavior here, and hit a case like this:

```


func.func @cse_multiple_regions(%c: i1, %t: i32) -> (i32, i32) {
  %init = "test.producer"() : () -> i32
  %r1 = scf.if %c -> (i32) {
    %r11 = scf.if %c -> (i32) {
      %0 = arith.addi %init, %init : i32
      scf.yield %0 : i32
    } else {
      %0 = arith.addi %init, %init : i32
      scf.yield %0 : i32
    }
    scf.yield %r11 : i32
  } else {
    scf.yield %t : i32
  }
  %r2 = scf.if %c -> (i32) {
    %r11 = scf.if %c -> (i32) {
      %0 = arith.addi %init, %init : i32
      scf.yield %0 : i32
    } else {
      %0 = arith.addi %init, %init : i32
      scf.yield %0 : i32
    }
    scf.yield %r11 : i32
  } else {
    scf.yield %t : i32
  }
  return %r1, %r2 : i32, i32
}
```

The top level scf.if are copy/pasted (so identical) and the CSE pass generates invalid IR, can you take a look?

```
 error: operand #0 does not dominate this use
      scf.yield %0 : i32
      ^
```

https://github.com/llvm/llvm-project/pull/180556