Index: llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
+++ llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
@@ -513,6 +513,11 @@
 
   bool runOnMachineFunction(MachineFunction &F) override;
 
+  bool allowTailDupPlacement() const {
+    assert(F);
+    return TailDupPlacement && !F->getTarget().requiresStructuredCFG();
+  }
+
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<MachineBranchProbabilityInfo>();
     AU.addRequired<MachineBlockFrequencyInfo>();
@@ -1018,7 +1023,7 @@
     MachineBasicBlock *Succ1 = BestA.Dest;
     MachineBasicBlock *Succ2 = BestB.Dest;
     // Check to see if tail-duplication would be profitable.
-    if (TailDupPlacement && shouldTailDuplicate(Succ2) &&
+    if (allowTailDupPlacement() && shouldTailDuplicate(Succ2) &&
         canTailDuplicateUnplacedPreds(BB, Succ2, Chain, BlockFilter) &&
         isProfitableToTailDup(BB, Succ2, MBPI->getEdgeProbability(BB, Succ1),
                               Chain, BlockFilter)) {
@@ -1044,7 +1049,7 @@
   return Result;
 }
 
-/// When the option TailDupPlacement is on, this method checks if the
+/// When the option allowTailDupPlacement() is on, this method checks if the
 /// fallthrough candidate block \p Succ (of block \p BB) can be tail-duplicated
 /// into all of its unplaced, unfiltered predecessors, that are not BB.
 bool MachineBlockPlacement::canTailDuplicateUnplacedPreds(
@@ -1493,7 +1498,7 @@
     if (hasBetterLayoutPredecessor(BB, Succ, SuccChain, SuccProb, RealSuccProb,
                                    Chain, BlockFilter)) {
       // If tail duplication would make Succ profitable, place it.
-      if (TailDupPlacement && shouldTailDuplicate(Succ))
+      if (allowTailDupPlacement() && shouldTailDuplicate(Succ))
         DupCandidates.push_back(std::make_tuple(SuccProb, Succ));
       continue;
     }
@@ -1702,7 +1707,7 @@
     auto Result = selectBestSuccessor(BB, Chain, BlockFilter);
     MachineBasicBlock* BestSucc = Result.BB;
     bool ShouldTailDup = Result.ShouldTailDup;
-    if (TailDupPlacement)
+    if (allowTailDupPlacement())
       ShouldTailDup |= (BestSucc && shouldTailDuplicate(BestSucc));
 
     // If an immediate successor isn't available, look for the best viable
@@ -1724,7 +1729,7 @@
 
     // Placement may have changed tail duplication opportunities.
     // Check for that now.
-    if (TailDupPlacement && BestSucc && ShouldTailDup) {
+    if (allowTailDupPlacement() && BestSucc && ShouldTailDup) {
       // If the chosen successor was duplicated into all its predecessors,
       // don't bother laying it out, just go round the loop again with BB as
       // the chain end.
@@ -2758,7 +2763,7 @@
       TailDupSize = TailDupPlacementAggressiveThreshold;
   }
 
-  if (TailDupPlacement) {
+  if (allowTailDupPlacement()) {
     MPDT = &getAnalysis<MachinePostDominatorTree>();
     if (MF.getFunction().optForSize())
       TailDupSize = 1;