1 files changed, 25 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 639b588766a..a469f893ce1 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -2730,6 +2730,31 @@ void MachineBlockPlacement::optimizeBranches() {
         TII->removeBranch(*ChainBB);
         TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl);
         ChainBB->updateTerminator();
+      } else if (Cond.empty() && TBB && ChainBB != TBB && 
+                 !TBB->canFallThrough()) {
+        // When ChainBB is unconditional branch to the TBB, and TBB has no 
+        // fallthrough predecessor and fallthrough successor, try to merge
+        // ChainBB and TBB. This is legal under the one of following conditions:
+        // 1. ChainBB is empty except for an unconditional branch.
+        // 2. TBB has only one predecessor.
+        MachineFunction::iterator I(TBB);
+        if (((TBB == &*F->begin()) || !std::prev(I)->canFallThrough()) &&
+             (TailDup.isSimpleBB(ChainBB) || (TBB->pred_size() == 1))) {
+          TII->removeBranch(*ChainBB);
+          ChainBB->removeSuccessor(TBB);
+
+          // Update the CFG.
+          for (MachineBasicBlock::pred_iterator PI = TBB->pred_begin(),
+               PE = TBB->pred_end(); PI != PE; PI++) 
+            (*PI)->ReplaceUsesOfBlockWith(TBB, ChainBB);
+
+          for (MachineBasicBlock *Succ : TBB->successors())
+            ChainBB->addSuccessor(Succ, MBPI->getEdgeProbability(TBB, Succ));
+
+          // Move all the instructions of TBB to ChainBB.
+          ChainBB->splice(ChainBB->end(), TBB, TBB->begin(), TBB->end());
+          F->remove(TBB);
+        }
       }
     }
   }