1 files changed, 66 insertions, 0 deletions
diff --git a/lib/CodeGen/MachineDominators.cpp b/lib/CodeGen/MachineDominators.cpp
index df60cf3..467a2e4 100644
--- a/lib/CodeGen/MachineDominators.cpp
+++ b/lib/CodeGen/MachineDominators.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace llvm;
 
@@ -59,3 +60,68 @@ void MachineDominatorTree::releaseMemory() {
 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
   DT->print(OS);
 }
+
+void MachineDominatorTree::applySplitCriticalEdges() const {
+  // Bail out early if there is nothing to do.
+  if (CriticalEdgesToSplit.empty())
+    return;
+
+  // For each element in CriticalEdgesToSplit, remember whether or not element
+  // is the new immediate domminator of its successor. The mapping is done by
+  // index, i.e., the information for the ith element of CriticalEdgesToSplit is
+  // the ith element of IsNewIDom.
+  SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
+  size_t Idx = 0;
+
+  // Collect all the dominance properties info, before invalidating
+  // the underlying DT.
+  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
+    // Update dominator information.
+    MachineBasicBlock *Succ = Edge.ToBB;
+    MachineDomTreeNode *SuccDTNode = DT->getNode(Succ);
+
+    for (MachineBasicBlock *PredBB : Succ->predecessors()) {
+      if (PredBB == Edge.NewBB)
+        continue;
+      // If we are in this situation:
+      // FromBB1        FromBB2
+      //    +              +
+      //   + +            + +
+      //  +   +          +   +
+      // ...  Split1  Split2 ...
+      //           +   +
+      //            + +
+      //             +
+      //            Succ
+      // Instead of checking the domiance property with Split2, we check it with
+      // FromBB2 since Split2 is still unknown of the underlying DT structure.
+      if (NewBBs.count(PredBB)) {
+        assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
+                                           "critical edge split has more "
+                                           "than one predecessor!");
+        PredBB = *PredBB->pred_begin();
+      }
+      if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) {
+        IsNewIDom[Idx] = false;
+        break;
+      }
+    }
+    ++Idx;
+  }
+
+  // Now, update DT with the collected dominance properties info.
+  Idx = 0;
+  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
+    // We know FromBB dominates NewBB.
+    MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB);
+
+    // If all the other predecessors of "Succ" are dominated by "Succ" itself
+    // then the new block is the new immediate dominator of "Succ". Otherwise,
+    // the new block doesn't dominate anything.
+    if (IsNewIDom[Idx])
+      DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode);
+    ++Idx;
+  }
+  NewBBs.clear();
+  CriticalEdgesToSplit.clear();
+}