2 files changed, 34 insertions, 35 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index b3dd3c9d724..d85cc40c372 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -170,7 +170,8 @@ bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
 
 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
                                      LoopInfo *LI, MemorySSAUpdater *MSSAU,
-                                     MemoryDependenceResults *MemDep) {
+                                     MemoryDependenceResults *MemDep,
+                                     bool PredecessorWithTwoSuccessors) {
   if (BB->hasAddressTaken())
     return false;
 
@@ -185,9 +186,24 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
     return false;
 
   // Can't merge if there are multiple distinct successors.
-  if (PredBB->getUniqueSuccessor() != BB)
+  if (!PredecessorWithTwoSuccessors && PredBB->getUniqueSuccessor() != BB)
     return false;
 
+  // Currently only allow PredBB to have two predecessors, one being BB.
+  // Update BI to branch to BB's only successor instead of BB.
+  BranchInst *PredBB_BI;
+  BasicBlock *NewSucc = nullptr;
+  unsigned FallThruPath;
+  if (PredecessorWithTwoSuccessors) {
+    if (!(PredBB_BI = dyn_cast<BranchInst>(PredBB->getTerminator())))
+      return false;
+    BranchInst *BB_JmpI = dyn_cast<BranchInst>(BB->getTerminator());
+    if (!BB_JmpI || !BB_JmpI->isUnconditional())
+      return false;
+    NewSucc = BB_JmpI->getSuccessor(0);
+    FallThruPath = PredBB_BI->getSuccessor(0) == BB ? 0 : 1;
+  }
+
   // Can't merge if there is PHI loop.
   for (PHINode &PN : BB->phis())
     for (Value *IncValue : PN.incoming_values())
@@ -246,11 +262,20 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
   // source...
   BB->replaceAllUsesWith(PredBB);
 
-  // Delete the unconditional branch from the predecessor...
-  PredBB->getInstList().pop_back();
+  if (PredecessorWithTwoSuccessors) {
+    // Delete the unconditional branch from BB.
+    BB->getInstList().pop_back();
 
-  // Move terminator instruction and add unreachable to now empty BB.
-  PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
+    // Update branch in the predecessor.
+    PredBB_BI->setSuccessor(FallThruPath, NewSucc);
+  } else {
+    // Delete the unconditional branch from the predecessor.
+    PredBB->getInstList().pop_back();
+
+    // Move terminator instruction.
+    PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
+  }
+  // Add unreachable to now empty BB.
   new UnreachableInst(BB->getContext(), BB);
 
   // Eliminate duplicate dbg.values describing the entry PHI node post-splice.
diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index 4765aa115d1..889ea5ca997 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -615,35 +615,9 @@ bool LoopRotate::simplifyLoopLatch(Loop *L) {
   LLVM_DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
                     << LastExit->getName() << "\n");
 
-  Instruction *FirstLatchInst = &*Latch->begin();
-  // If there's nothing to move, mark the starting instruction as the last
-  // instruction in the block.
-  if (FirstLatchInst == Jmp)
-    FirstLatchInst = BI;
-
-  // Hoist the instructions from Latch into LastExit.
-  LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
-                                 Latch->begin(), Jmp->getIterator());
-
-  // Update MemorySSA
-  if (MSSAU)
-    MSSAU->moveAllAfterMergeBlocks(Latch, LastExit, FirstLatchInst);
-
-  unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
-  BasicBlock *Header = Jmp->getSuccessor(0);
-  assert(Header == L->getHeader() && "expected a backward branch");
-
-  // Remove Latch from the CFG so that LastExit becomes the new Latch.
-  BI->setSuccessor(FallThruPath, Header);
-  Latch->replaceSuccessorsPhiUsesWith(LastExit);
-  Jmp->eraseFromParent();
-
-  // Nuke the Latch block.
-  assert(Latch->empty() && "unable to evacuate Latch");
-  LI->removeBlock(Latch);
-  if (DT)
-    DT->eraseNode(Latch);
-  Latch->eraseFromParent();
+  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
+  MergeBlockIntoPredecessor(Latch, &DTU, LI, MSSAU, nullptr,
+                            /*PredecessorWithTwoSuccessors=*/true);
 
   if (MSSAU && VerifyMemorySSA)
     MSSAU->getMemorySSA()->verifyMemorySSA();