[llvm] [DomTreeUpdater] Handle critical edge splitting (PR #100856)

[via llvm-commits]

================
@@ -146,8 +152,25 @@ class GenericDomTreeUpdater {
   /// 2. It is illegal to submit any update that has already been submitted,
   /// i.e., you are supposed not to insert an existent edge or delete a
   /// nonexistent edge.
+  /// 3. This kind updates are incompatible with critical edge splitting
+  /// updates, call this method will apply all critical edge updates in
+  /// lazy mode. It is not recommended to interleave applyUpdates and
+  /// applyUpdatesForCriticalEdgeSplitting.
----------------
paperchalice wrote:

Sorry for my poor expression.
In lazy mode
```c++
DomTreeUpdater DTU(...); // Assume in lazy mode.
DTU.applyUpdates({...}); // Several general updates.
DTU.applyUpdatesForCriticalEdgeSplitting(...); // Is equivalent to DTU.flush(); DTU.applyUpdatesForCriticalEdgeSplitting(...)
```
Because `cfg::Update` doesn't model the update kind for critical edge splitting.

https://github.com/llvm/llvm-project/pull/100856