[llvm] [VPlan] Introduce child regions as VPlan transform. (PR #129402)

[via llvm-commits]

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@@ -98,4 +120,9 @@ void VPlanTransforms::introduceTopLevelVectorLoopRegion(
                                ScalarLatchTerm->getDebugLoc(), "cmp.n");
   Builder.createNaryOp(VPInstruction::BranchOnCond, {Cmp},
                        ScalarLatchTerm->getDebugLoc());
+
+  for (VPBlockBase *HeaderVPBB :
+       vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry())) {
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ayalz wrote:

The cfg is flat so both shallow and deep traverse all blocks?

https://github.com/llvm/llvm-project/pull/129402