[llvm] [VPlan] Use DomTreeUpdater to automatically update DT for vector loop. (PR #92525)

[via llvm-commits]

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@@ -891,13 +899,9 @@ void VPlan::execute(VPTransformState *State) {
     }
   }
 
-  // We do not attempt to preserve DT for outer loop vectorization currently.
-  if (!EnableVPlanNativePath) {
-    BasicBlock *VectorHeaderBB = State->CFG.VPBB2IRBB[Header];
-    State->DT->addNewBlock(VectorHeaderBB, VectorPreHeader);
-    updateDominatorTree(State->DT, VectorHeaderBB, VectorLatchBB,
-                        State->CFG.ExitBB);
-  }
+  State->CFG.DTU.flush();
+  assert(EnableVPlanNativePath || State->CFG.DTU.getDomTree().verify(
+                                      DominatorTree::VerificationLevel::Fast));
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ayalz wrote:

```suggestion
  // DT is currently updated for non-native path only.
  assert(EnableVPlanNativePath || State->CFG.DTU.getDomTree().verify(
                                      DominatorTree::VerificationLevel::Fast));
```
(retaining the comment)

https://github.com/llvm/llvm-project/pull/92525