[Mlir-commits] [mlir] [mlir][RemoveDeadValues] Simplify branch op handling using ub.poison (PR #182711)

[Matthias Springer]

================
@@ -35,20 +35,26 @@ module @named_module_acceptable {
 func.func @acceptable_ir_has_cleanable_loop_of_conditional_and_branch_op(%arg0: i1) {
   %non_live = arith.constant 0 : i32
   // CHECK-NOT: arith.constant
+  // CHECK-CANONICALIZE-NOT: arith.constant
   cf.br ^bb1(%non_live : i32)
-  // CHECK: cf.br ^[[BB1:bb[0-9]+]]
+  // CHECK: cf.br ^[[BB1:bb[0-9]+]](%{{.*}} : i32)
+  // CHECK-CANONICALIZE: cf.br ^[[BB1:bb[0-9]+]](%{{.*}} : i32)
 ^bb1(%non_live_1 : i32):
-  // CHECK: ^[[BB1]]:
+  // CHECK: ^[[BB1]](%{{.*}}: i32):
+  // CHECK-CANONICALIZE: ^[[BB1]](%{{.*}}: i32):
   %non_live_5 = arith.constant 1 : i32
   cf.br ^bb3(%non_live_1, %non_live_5 : i32, i32)
-  // CHECK: cf.br ^[[BB3:bb[0-9]+]]
-  // CHECK-NOT: i32
+  // CHECK: cf.br ^[[BB3:bb[0-9]+]](%{{.*}}, %{{.*}} : i32, i32)
+  // CHECK-CANONICALIZE: cf.br ^[[BB3:bb[0-9]+]](%{{.*}}, %{{.*}} : i32, i32)
----------------
matthias-springer wrote:

Hmm, actually the canonicalizer successfully simplifies the above IR, even without `-cse`:
```
  func.func @acceptable_ir_has_cleanable_loop_of_conditional_and_branch_op(%arg0: i1) {
    cf.br ^bb1
  ^bb1:  // 2 preds: ^bb0, ^bb1
    cf.cond_br %arg0, ^bb1, ^bb2
  ^bb2:  // pred: ^bb1
    return
  }
```

A few patterns may still be missing. E.g., it does nothing on this IR:
```
func.func @foo(%val: f32, %c:i1) -> f32{
  cf.cond_br %c, ^bb0(%val : f32), ^bb1(%val : f32)
^bb0(%arg0: f32):
  return %arg0: f32
^bb1(%arg1: f32):
  return %arg1: f32
}
```


https://github.com/llvm/llvm-project/pull/182711