[llvm] [VPlan] Retain exit conditions and edges in initial VPlan (NFC). (PR #137709)

[via llvm-commits]

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@@ -424,22 +408,25 @@ static void createLoopRegion(VPlan &Plan, VPBlockBase *HeaderVPB) {
 
   VPBlockUtils::disconnectBlocks(PreheaderVPBB, HeaderVPB);
   VPBlockUtils::disconnectBlocks(LatchVPBB, HeaderVPB);
-  VPBlockBase *Succ = LatchVPBB->getSingleSuccessor();
-  assert(LatchVPBB->getNumSuccessors() <= 1 &&
-         "Latch has more than one successor");
-  if (Succ)
-    VPBlockUtils::disconnectBlocks(LatchVPBB, Succ);
-
-  auto *R = Plan.createVPRegionBlock(HeaderVPB, LatchVPBB, "",
-                                     false /*isReplicator*/);
-  // All VPBB's reachable shallowly from HeaderVPB belong to top level loop,
-  // because VPlan is expected to end at top level latch disconnected above.
+  VPBlockBase *LatchExitVPB = LatchVPBB->getSingleSuccessor();
+  assert(LatchExitVPB && "Latch expected to be left with a single successor");
+
+  // Create an empty region first and insert it between PreheaderVPBB and
+  // LatchExitVPB, taking care to preserve the original predecessor & successor
+  // order of blocks. Set region entry and exiting after both HeaderVPB and
+  // LatchVPBB have been disconnected from their predecessors/successors.
+  auto *R = Plan.createVPRegionBlock("", false /*isReplicator*/);
+  VPBlockUtils::insertOnEdge(LatchVPBB, LatchExitVPB, R);
+  VPBlockUtils::disconnectBlocks(LatchVPBB, R);
+  VPBlockUtils::connectBlocks(PreheaderVPBB, R);
+  R->setEntry(HeaderVPB);
+  R->setExiting(LatchVPBB);
+
+  // All VPBB's reachable shallowly from HeaderVPB belong to the current region.
+  SmallPtrSet<VPBlockBase *, 2> ExitBlocks(Plan.getExitBlocks().begin(),
+                                           Plan.getExitBlocks().end());
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ayalz wrote:

```suggestion
```
?

https://github.com/llvm/llvm-project/pull/137709