Refactor code to create getFallThrough method in MachineBasicBlock.

Differential Revision: https://reviews.llvm.org/D27264

llvm-svn: 299227

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -688,16 +688,16 @@ bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
   return std::next(I) == MachineFunction::const_iterator(MBB);
 }
 
-bool MachineBasicBlock::canFallThrough() {
+MachineBasicBlock *MachineBasicBlock::getFallThrough() {
   MachineFunction::iterator Fallthrough = getIterator();
   ++Fallthrough;
   // If FallthroughBlock is off the end of the function, it can't fall through.
   if (Fallthrough == getParent()->end())
-    return false;
+    return nullptr;
 
   // If FallthroughBlock isn't a successor, no fallthrough is possible.
   if (!isSuccessor(&*Fallthrough))
-    return false;
+    return nullptr;
 
   // Analyze the branches, if any, at the end of the block.
   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
@@ -709,25 +709,31 @@ bool MachineBasicBlock::canFallThrough() {
     // is possible. The isPredicated check is needed because this code can be
     // called during IfConversion, where an instruction which is normally a
     // Barrier is predicated and thus no longer an actual control barrier.
-    return empty() || !back().isBarrier() || TII->isPredicated(back());
+    return (empty() || !back().isBarrier() || TII->isPredicated(back()))
+               ? &*Fallthrough
+               : nullptr;
   }
 
   // If there is no branch, control always falls through.
-  if (!TBB) return true;
+  if (!TBB) return &*Fallthrough;
 
   // If there is some explicit branch to the fallthrough block, it can obviously
   // reach, even though the branch should get folded to fall through implicitly.
   if (MachineFunction::iterator(TBB) == Fallthrough ||
       MachineFunction::iterator(FBB) == Fallthrough)
-    return true;
+    return &*Fallthrough;
 
   // If it's an unconditional branch to some block not the fall through, it
   // doesn't fall through.
-  if (Cond.empty()) return false;
+  if (Cond.empty()) return nullptr;
 
   // Otherwise, if it is conditional and has no explicit false block, it falls
   // through.
-  return FBB == nullptr;
+  return (FBB == nullptr) ? &*Fallthrough : nullptr;
+}
+
+bool MachineBasicBlock::canFallThrough() {
+  return getFallThrough() != nullptr;
 }
 
 MachineBasicBlock *MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ,