MC CFG: Split MCBasicBlocks to mirror atom splitting.

When an MCTextAtom is split, all MCBasicBlocks backed by it are
automatically split, with a fallthrough between both blocks, and
the successors moved to the second block.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188881 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCFunction.cpp b/lib/MC/MCFunction.cpp
index 300ab5b..85e88e5 100644
--- a/lib/MC/MCFunction.cpp
+++ b/lib/MC/MCFunction.cpp
@@ -46,8 +46,9 @@
 // MCBasicBlock
 
 MCBasicBlock::MCBasicBlock(const MCTextAtom &Insts, MCFunction *Parent)
-  : Insts(&Insts), Parent(Parent)
-{}
+  : Insts(&Insts), Parent(Parent) {
+  getParent()->getParent()->trackBBForAtom(&Insts, this);
+}
 
 void MCBasicBlock::addSuccessor(const MCBasicBlock *MCBB) {
   if (!isSuccessor(MCBB))
@@ -68,3 +69,14 @@
   return std::find(Predecessors.begin(), Predecessors.end(),
                    MCBB) != Predecessors.end();
 }
+
+void MCBasicBlock::splitBasicBlock(MCBasicBlock *SplitBB) {
+  assert(Insts->getEndAddr() + 1 == SplitBB->Insts->getBeginAddr() &&
+         "Splitting unrelated basic blocks!");
+  SplitBB->addPredecessor(this);
+  assert(SplitBB->Successors.empty() &&
+         "Split basic block shouldn't already have successors!");
+  SplitBB->Successors = Successors;
+  Successors.clear();
+  addSuccessor(SplitBB);
+}