[llvm] [VPlan] Handle early exit before forming regions. (NFC) (PR #138393)

[via llvm-commits]

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@@ -2488,64 +2488,86 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan,
     R->eraseFromParent();
 }
 
-void VPlanTransforms::handleUncountableEarlyExit(
-    VPlan &Plan, Loop *OrigLoop, BasicBlock *UncountableExitingBlock,
-    VPRecipeBuilder &RecipeBuilder, VFRange &Range) {
-  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
-  auto *LatchVPBB = cast<VPBasicBlock>(LoopRegion->getExiting());
+void VPlanTransforms::handleUncountableEarlyExit(VPlan &Plan,
+                                                 VPBasicBlock *HeaderVPBB,
+                                                 VPBasicBlock *LatchVPBB,
+                                                 VFRange &Range) {
+  // First find the uncountable early exiting block by looking at the
+  // predecessors of the exit blocks.
+  VPBlockBase *MiddleVPBB = LatchVPBB->getSuccessors()[0];
+  VPBasicBlock *EarlyExitingVPBB = nullptr;
+  VPIRBasicBlock *EarlyExitVPBB = nullptr;
+  for (auto *EB : Plan.getExitBlocks()) {
+    for (VPBlockBase *Pred : EB->getPredecessors()) {
+      if (Pred != MiddleVPBB) {
+        EarlyExitingVPBB = cast<VPBasicBlock>(Pred);
+        EarlyExitVPBB = EB;
+        break;
+      }
+    }
+  }
+  assert(EarlyExitVPBB && "Must have a early exiting block.");
+  assert(all_of(Plan.getExitBlocks(),
+                [EarlyExitingVPBB, MiddleVPBB](VPIRBasicBlock *EB) {
+                  return all_of(
+                      EB->getPredecessors(),
+                      [EarlyExitingVPBB, MiddleVPBB](VPBlockBase *Pred) {
+                        return Pred == EarlyExitingVPBB || Pred == MiddleVPBB;
+                      });
+                }) &&
+         "All exit blocks must only have EarlyExitingVPBB or MiddleVPBB as "
----------------
ayalz wrote:

```suggestion
         "Every exit block must have EarlyExitingVPBB and/or MiddleVPBB as "
```
better fits in verifier?

https://github.com/llvm/llvm-project/pull/138393