2 files changed, 29 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 32c0bcf310c..89ca641cfe0 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -324,6 +324,14 @@ class MachineBlockPlacement : public MachineFunctionPass {
   /// between basic blocks.
   DenseMap<MachineBasicBlock *, BlockChain *> BlockToChain;
 
+#ifndef NDEBUG
+  /// The set of basic blocks that have terminators that cannot be fully
+  /// analyzed.  These basic blocks cannot be re-ordered safely by
+  /// MachineBlockPlacement, and we must preserve physical layout of these
+  /// blocks and their successors through the pass.
+  SmallPtrSet<MachineBasicBlock *, 4> BlocksWithUnanalyzableExits;
+#endif
+
   /// Decrease the UnscheduledPredecessors count for all blocks in chain, and
   /// if the count goes to 0, add them to the appropriate work list.
   void markChainSuccessors(BlockChain &Chain, MachineBasicBlock *LoopHeaderBB,
@@ -1589,6 +1597,7 @@ void MachineBlockPlacement::buildCFGChains() {
                    << getBlockName(BB) << " -> " << getBlockName(NextBB)
                    << "\n");
       Chain->merge(NextBB, nullptr);
+      BlocksWithUnanalyzableExits.insert(&*BB);
       FI = NextFI;
       BB = NextBB;
     }
@@ -1661,6 +1670,19 @@ void MachineBlockPlacement::buildCFGChains() {
     Cond.clear();
     MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
 
+#ifndef NDEBUG
+    if (!BlocksWithUnanalyzableExits.count(PrevBB)) {
+      // Given the exact block placement we chose, we may actually not _need_ to
+      // be able to edit PrevBB's terminator sequence, but not being _able_ to
+      // do that at this point is a bug.
+      assert((!TII->analyzeBranch(*PrevBB, TBB, FBB, Cond) ||
+              !PrevBB->canFallThrough()) &&
+             "Unexpected block with un-analyzable fallthrough!");
+      Cond.clear();
+      TBB = FBB = nullptr;
+    }
+#endif
+
     // The "PrevBB" is not yet updated to reflect current code layout, so,
     //   o. it may fall-through to a block without explicit "goto" instruction
     //      before layout, and no longer fall-through it after layout; or
diff --git a/llvm/lib/CodeGen/TailDuplicator.cpp b/llvm/lib/CodeGen/TailDuplicator.cpp
index 06aa5e1fc0d..7709236bbaa 100644
--- a/llvm/lib/CodeGen/TailDuplicator.cpp
+++ b/llvm/lib/CodeGen/TailDuplicator.cpp
@@ -550,8 +550,8 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
   // blocks with unanalyzable fallthrough get layed out contiguously.
   MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
   SmallVector<MachineOperand, 4> PredCond;
-  if (TII->analyzeBranch(TailBB, PredTBB, PredFBB, PredCond, true)
-      && TailBB.canFallThrough())
+  if (TII->analyzeBranch(TailBB, PredTBB, PredFBB, PredCond) &&
+      TailBB.canFallThrough())
     return false;
 
   // If the target has hardware branch prediction that can handle indirect
@@ -660,7 +660,7 @@ bool TailDuplicator::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
 
     MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
     SmallVector<MachineOperand, 4> PredCond;
-    if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+    if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond))
       return false;
 
     if (!PredCond.empty())
@@ -687,7 +687,7 @@ bool TailDuplicator::duplicateSimpleBB(
 
     MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
     SmallVector<MachineOperand, 4> PredCond;
-    if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+    if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond))
       continue;
 
     Changed = true;
@@ -750,7 +750,7 @@ bool TailDuplicator::canTailDuplicate(MachineBasicBlock *TailBB,
 
   MachineBasicBlock *PredTBB, *PredFBB;
   SmallVector<MachineOperand, 4> PredCond;
-  if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+  if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond))
     return false;
   if (!PredCond.empty())
     return false;
@@ -833,7 +833,7 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
     // Simplify
     MachineBasicBlock *PredTBB, *PredFBB;
     SmallVector<MachineOperand, 4> PredCond;
-    TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
+    TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond);
 
     NumTailDupAdded += TailBB->size() - 1; // subtract one for removed branch
 
@@ -861,7 +861,7 @@ bool TailDuplicator::tailDuplicate(bool IsSimple, MachineBasicBlock *TailBB,
   if (PrevBB->succ_size() == 1 &&
       // Layout preds are not always CFG preds. Check.
       *PrevBB->succ_begin() == TailBB &&
-      !TII->analyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) &&
+      !TII->analyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond) &&
       PriorCond.empty() &&
       (!PriorTBB || PriorTBB == TailBB) &&
       TailBB->pred_size() == 1 &&