StructurizeCFG: Use LoopInfo analysis for better loop detection

We were assuming that each back-edge in a region represented a unique
loop, which is not always the case.  We need to use LoopInfo to
correctly determine which back-edges are loops.

llvm-svn: 223199

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp b/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
index b9673ed655e..7fe87f9319b 100644
--- a/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
+++ b/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp
@@ -10,6 +10,7 @@
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SCCIterator.h"
+#include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/RegionInfo.h"
 #include "llvm/Analysis/RegionIterator.h"
 #include "llvm/Analysis/RegionPass.h"
@@ -166,6 +167,7 @@ class StructurizeCFG : public RegionPass {
   Region *ParentRegion;
 
   DominatorTree *DT;
+  LoopInfo *LI;
 
   RNVector Order;
   BBSet Visited;
@@ -247,6 +249,7 @@ public:
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequiredID(LowerSwitchID);
     AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addRequired<LoopInfo>();
     AU.addPreserved<DominatorTreeWrapperPass>();
     RegionPass::getAnalysisUsage(AU);
   }
@@ -301,8 +304,9 @@ void StructurizeCFG::analyzeLoops(RegionNode *N) {
     for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
       BasicBlock *Succ = Term->getSuccessor(i);
 
-      if (Visited.count(Succ))
+      if (Visited.count(Succ) && LI->isLoopHeader(Succ) ) {
         Loops[Succ] = BB;
+      }
     }
   }
 }
@@ -862,6 +866,7 @@ bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
   ParentRegion = R;
 
   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  LI = &getAnalysis<LoopInfo>();
 
   orderNodes();
   collectInfos();