[VPlan] Introduce VPLoopInfo analysis.

The patch introduces loop analysis (VPLoopInfo/VPLoop) for VPBlockBases.
This analysis will be necessary to perform some H-CFG transformations and
detect and introduce regions representing a loop in the H-CFG.

Reviewers: fhahn, rengolin, mkuper, hfinkel, mssimpso

Reviewed By: fhahn 

Differential Revision: https://reviews.llvm.org/D48816

llvm-svn: 338346
diff --git a/llvm/lib/Transforms/Vectorize/VPlanHCFGBuilder.cpp b/llvm/lib/Transforms/Vectorize/VPlanHCFGBuilder.cpp
index 26e112e..b6307ac 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanHCFGBuilder.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanHCFGBuilder.cpp
@@ -342,4 +342,10 @@
   VPDomTree.recalculate(*TopRegion);
   LLVM_DEBUG(dbgs() << "Dominator Tree after building the plain CFG.\n";
              VPDomTree.print(dbgs()));
+
+  // Compute VPLInfo and keep it in Plan.
+  VPLoopInfo &VPLInfo = Plan.getVPLoopInfo();
+  VPLInfo.analyze(VPDomTree);
+  LLVM_DEBUG(dbgs() << "VPLoop Info After buildPlainCFG:\n";
+             VPLInfo.print(dbgs()));
 }