1 files changed, 8 insertions, 9 deletions
diff --git a/llvm/lib/Transforms/Utils/FlattenCFG.cpp b/llvm/lib/Transforms/Utils/FlattenCFG.cpp
index ddd3f597ae01..2fb2ab82e41a 100644
--- a/llvm/lib/Transforms/Utils/FlattenCFG.cpp
+++ b/llvm/lib/Transforms/Utils/FlattenCFG.cpp
@@ -145,9 +145,7 @@ bool FlattenCFGOpt::FlattenParallelAndOr(BasicBlock *BB, IRBuilder<> &Builder) {
 
   // Check predecessors of \param BB.
   SmallPtrSet<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
-  for (SmallPtrSetIterator<BasicBlock *> PI = Preds.begin(), PE = Preds.end();
-       PI != PE; ++PI) {
-    BasicBlock *Pred = *PI;
+  for (BasicBlock *Pred : Preds) {
     BranchInst *PBI = dyn_cast<BranchInst>(Pred->getTerminator());
 
     // All predecessors should terminate with a branch.
@@ -286,9 +284,8 @@ bool FlattenCFGOpt::FlattenParallelAndOr(BasicBlock *BB, IRBuilder<> &Builder) {
   do {
     CB = PBI->getSuccessor(1 - Idx);
     // Delete the conditional branch.
-    FirstCondBlock->getInstList().pop_back();
-    FirstCondBlock->getInstList()
-        .splice(FirstCondBlock->end(), CB->getInstList());
+    FirstCondBlock->back().eraseFromParent();
+    FirstCondBlock->splice(FirstCondBlock->end(), CB);
     PBI = cast<BranchInst>(FirstCondBlock->getTerminator());
     Value *CC = PBI->getCondition();
     // Merge conditions.
@@ -431,6 +428,9 @@ bool FlattenCFGOpt::MergeIfRegion(BasicBlock *BB, IRBuilder<> &Builder) {
     return false;
 
   BasicBlock *FirstEntryBlock = CInst1->getParent();
+  // Don't die trying to process degenerate/unreachable code.
+  if (FirstEntryBlock == SecondEntryBlock)
+    return false;
 
   // Either then-path or else-path should be empty.
   bool InvertCond2 = false;
@@ -479,9 +479,8 @@ bool FlattenCFGOpt::MergeIfRegion(BasicBlock *BB, IRBuilder<> &Builder) {
   }
 
   // Merge \param SecondEntryBlock into \param FirstEntryBlock.
-  FirstEntryBlock->getInstList().pop_back();
-  FirstEntryBlock->getInstList()
-      .splice(FirstEntryBlock->end(), SecondEntryBlock->getInstList());
+  FirstEntryBlock->back().eraseFromParent();
+  FirstEntryBlock->splice(FirstEntryBlock->end(), SecondEntryBlock);
   BranchInst *PBI = cast<BranchInst>(FirstEntryBlock->getTerminator());
   assert(PBI->getCondition() == CInst2);
   BasicBlock *SaveInsertBB = Builder.GetInsertBlock();