Move StructurizeCFG out of R600 to generic Transforms.

Register it with PassManager

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184343 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/CMakeLists.txt

@@ -30,6 +30,7 @@ add_llvm_library(LLVMScalarOpts
   SimplifyCFGPass.cpp
   SimplifyLibCalls.cpp
   Sink.cpp
+  StructurizeCFG.cpp
   TailRecursionElimination.cpp
   )
 

lib/Transforms/Scalar/Scalar.cpp

@@ -58,6 +58,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeSROA_DTPass(Registry);
   initializeSROA_SSAUpPass(Registry);
   initializeCFGSimplifyPassPass(Registry);
+  initializeStructurizeCFGPass(Registry);
   initializeSimplifyLibCallsPass(Registry);
   initializeSinkingPass(Registry);
   initializeTailCallElimPass(Registry);

lib/Transforms/Scalar/StructurizeCFG.cpp

@@ -0,0 +1,879 @@
+//===-- StructurizeCFG.cpp ------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "structurizecfg"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/Analysis/RegionInfo.h"
+#include "llvm/Analysis/RegionIterator.h"
+#include "llvm/Analysis/RegionPass.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/PatternMatch.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+
+using namespace llvm;
+using namespace llvm::PatternMatch;
+
+namespace {
+
+// Definition of the complex types used in this pass.
+
+typedef std::pair<BasicBlock *, Value *> BBValuePair;
+
+typedef SmallVector<RegionNode*, 8> RNVector;
+typedef SmallVector<BasicBlock*, 8> BBVector;
+typedef SmallVector<BranchInst*, 8> BranchVector;
+typedef SmallVector<BBValuePair, 2> BBValueVector;
+
+typedef SmallPtrSet<BasicBlock *, 8> BBSet;
+
+typedef MapVector<PHINode *, BBValueVector> PhiMap;
+typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;
+
+typedef DenseMap<DomTreeNode *, unsigned> DTN2UnsignedMap;
+typedef DenseMap<BasicBlock *, PhiMap> BBPhiMap;
+typedef DenseMap<BasicBlock *, Value *> BBPredicates;
+typedef DenseMap<BasicBlock *, BBPredicates> PredMap;
+typedef DenseMap<BasicBlock *, BasicBlock*> BB2BBMap;
+
+// The name for newly created blocks.
+
+static const char *FlowBlockName = "Flow";
+
+/// @brief Find the nearest common dominator for multiple BasicBlocks
+///
+/// Helper class for StructurizeCFG
+/// TODO: Maybe move into common code
+class NearestCommonDominator {
+  DominatorTree *DT;
+
+  DTN2UnsignedMap IndexMap;
+
+  BasicBlock *Result;
+  unsigned ResultIndex;
+  bool ExplicitMentioned;
+
+public:
+  /// \brief Start a new query
+  NearestCommonDominator(DominatorTree *DomTree) {
+    DT = DomTree;
+    Result = 0;
+  }
+
+  /// \brief Add BB to the resulting dominator
+  void addBlock(BasicBlock *BB, bool Remember = true) {
+    DomTreeNode *Node = DT->getNode(BB);
+
+    if (Result == 0) {
+      unsigned Numbering = 0;
+      for (;Node;Node = Node->getIDom())
+        IndexMap[Node] = ++Numbering;
+      Result = BB;
+      ResultIndex = 1;
+      ExplicitMentioned = Remember;
+      return;
+    }
+
+    for (;Node;Node = Node->getIDom())
+      if (IndexMap.count(Node))
+        break;
+      else
+        IndexMap[Node] = 0;
+
+    assert(Node && "Dominator tree invalid!");
+
+    unsigned Numbering = IndexMap[Node];
+    if (Numbering > ResultIndex) {
+      Result = Node->getBlock();
+      ResultIndex = Numbering;
+      ExplicitMentioned = Remember && (Result == BB);
+    } else if (Numbering == ResultIndex) {
+      ExplicitMentioned |= Remember;
+    }
+  }
+
+  /// \brief Is "Result" one of the BBs added with "Remember" = True?
+  bool wasResultExplicitMentioned() {
+    return ExplicitMentioned;
+  }
+
+  /// \brief Get the query result
+  BasicBlock *getResult() {
+    return Result;
+  }
+};
+
+/// @brief Transforms the control flow graph on one single entry/exit region
+/// at a time.
+///
+/// After the transform all "If"/"Then"/"Else" style control flow looks like
+/// this:
+///
+/// \verbatim
+/// 1
+/// ||
+/// | |
+/// 2 |
+/// | /
+/// |/
+/// 3
+/// ||   Where:
+/// | |  1 = "If" block, calculates the condition
+/// 4 |  2 = "Then" subregion, runs if the condition is true
+/// | /  3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
+/// |/   4 = "Else" optional subregion, runs if the condition is false
+/// 5    5 = "End" block, also rejoins the control flow
+/// \endverbatim
+///
+/// Control flow is expressed as a branch where the true exit goes into the
+/// "Then"/"Else" region, while the false exit skips the region
+/// The condition for the optional "Else" region is expressed as a PHI node.
+/// The incomming values of the PHI node are true for the "If" edge and false
+/// for the "Then" edge.
+///
+/// Additionally to that even complicated loops look like this:
+///
+/// \verbatim
+/// 1
+/// ||
+/// | |
+/// 2 ^  Where:
+/// | /  1 = "Entry" block
+/// |/   2 = "Loop" optional subregion, with all exits at "Flow" block
+/// 3    3 = "Flow" block, with back edge to entry block
+/// |
+/// \endverbatim
+///
+/// The back edge of the "Flow" block is always on the false side of the branch
+/// while the true side continues the general flow. So the loop condition
+/// consist of a network of PHI nodes where the true incoming values expresses
+/// breaks and the false values expresses continue states.
+class StructurizeCFG : public RegionPass {
+  Type *Boolean;
+  ConstantInt *BoolTrue;
+  ConstantInt *BoolFalse;
+  UndefValue *BoolUndef;
+
+  Function *Func;
+  Region *ParentRegion;
+
+  DominatorTree *DT;
+
+  RNVector Order;
+  BBSet Visited;
+
+  BBPhiMap DeletedPhis;
+  BB2BBVecMap AddedPhis;
+
+  PredMap Predicates;
+  BranchVector Conditions;
+
+  BB2BBMap Loops;
+  PredMap LoopPreds;
+  BranchVector LoopConds;
+
+  RegionNode *PrevNode;
+
+  void orderNodes();
+
+  void analyzeLoops(RegionNode *N);
+
+  Value *invert(Value *Condition);
+
+  Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
+
+  void gatherPredicates(RegionNode *N);
+
+  void collectInfos();
+
+  void insertConditions(bool Loops);
+
+  void delPhiValues(BasicBlock *From, BasicBlock *To);
+
+  void addPhiValues(BasicBlock *From, BasicBlock *To);
+
+  void setPhiValues();
+
+  void killTerminator(BasicBlock *BB);
+
+  void changeExit(RegionNode *Node, BasicBlock *NewExit,
+                  bool IncludeDominator);
+
+  BasicBlock *getNextFlow(BasicBlock *Dominator);
+
+  BasicBlock *needPrefix(bool NeedEmpty);
+
+  BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
+
+  void setPrevNode(BasicBlock *BB);
+
+  bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
+
+  bool isPredictableTrue(RegionNode *Node);
+
+  void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
+
+  void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
+
+  void createFlow();
+
+  void rebuildSSA();
+
+public:
+  static char ID;
+
+  StructurizeCFG() :
+    RegionPass(ID) {
+    initializeRegionInfoPass(*PassRegistry::getPassRegistry());
+  }
+
+  using Pass::doInitialization;
+  virtual bool doInitialization(Region *R, RGPassManager &RGM);
+
+  virtual bool runOnRegion(Region *R, RGPassManager &RGM);
+
+  virtual const char *getPassName() const {
+    return "Structurize control flow";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addRequired<DominatorTree>();
+    AU.addPreserved<DominatorTree>();
+    RegionPass::getAnalysisUsage(AU);
+  }
+};
+
+} // end anonymous namespace
+
+char StructurizeCFG::ID = 0;
+
+INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(RegionInfo)
+INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",
+                    false, false)
+
+/// \brief Initialize the types and constants used in the pass
+bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
+  LLVMContext &Context = R->getEntry()->getContext();
+
+  Boolean = Type::getInt1Ty(Context);
+  BoolTrue = ConstantInt::getTrue(Context);
+  BoolFalse = ConstantInt::getFalse(Context);
+  BoolUndef = UndefValue::get(Boolean);
+
+  return false;
+}
+
+/// \brief Build up the general order of nodes
+void StructurizeCFG::orderNodes() {
+  scc_iterator<Region *> I = scc_begin(ParentRegion),
+                         E = scc_end(ParentRegion);
+  for (Order.clear(); I != E; ++I) {
+    std::vector<RegionNode *> &Nodes = *I;
+    Order.append(Nodes.begin(), Nodes.end());
+  }
+}
+
+/// \brief Determine the end of the loops
+void StructurizeCFG::analyzeLoops(RegionNode *N) {
+  if (N->isSubRegion()) {
+    // Test for exit as back edge
+    BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
+    if (Visited.count(Exit))
+      Loops[Exit] = N->getEntry();
+
+  } else {
+    // Test for sucessors as back edge
+    BasicBlock *BB = N->getNodeAs<BasicBlock>();
+    BranchInst *Term = cast<BranchInst>(BB->getTerminator());
+
+    for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
+      BasicBlock *Succ = Term->getSuccessor(i);
+
+      if (Visited.count(Succ))
+        Loops[Succ] = BB;
+    }
+  }
+}
+
+/// \brief Invert the given condition
+Value *StructurizeCFG::invert(Value *Condition) {
+  // First: Check if it's a constant
+  if (Condition == BoolTrue)
+    return BoolFalse;
+
+  if (Condition == BoolFalse)
+    return BoolTrue;
+
+  if (Condition == BoolUndef)
+    return BoolUndef;
+
+  // Second: If the condition is already inverted, return the original value
+  if (match(Condition, m_Not(m_Value(Condition))))
+    return Condition;
+
+  // Third: Check all the users for an invert
+  BasicBlock *Parent = cast<Instruction>(Condition)->getParent();
+  for (Value::use_iterator I = Condition->use_begin(),
+       E = Condition->use_end(); I != E; ++I) {
+
+    Instruction *User = dyn_cast<Instruction>(*I);
+    if (!User || User->getParent() != Parent)
+      continue;
+
+    if (match(*I, m_Not(m_Specific(Condition))))
+      return *I;
+  }
+
+  // Last option: Create a new instruction
+  return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
+}
+
+/// \brief Build the condition for one edge
+Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
+                                      bool Invert) {
+  Value *Cond = Invert ? BoolFalse : BoolTrue;
+  if (Term->isConditional()) {
+    Cond = Term->getCondition();
+
+    if (Idx != (unsigned)Invert)
+      Cond = invert(Cond);
+  }
+  return Cond;
+}
+
+/// \brief Analyze the predecessors of each block and build up predicates
+void StructurizeCFG::gatherPredicates(RegionNode *N) {
+  RegionInfo *RI = ParentRegion->getRegionInfo();
+  BasicBlock *BB = N->getEntry();
+  BBPredicates &Pred = Predicates[BB];
+  BBPredicates &LPred = LoopPreds[BB];
+
+  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
+       PI != PE; ++PI) {
+
+    // Ignore it if it's a branch from outside into our region entry
+    if (!ParentRegion->contains(*PI))
+      continue;
+
+    Region *R = RI->getRegionFor(*PI);
+    if (R == ParentRegion) {
+
+      // It's a top level block in our region
+      BranchInst *Term = cast<BranchInst>((*PI)->getTerminator());
+      for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
+        BasicBlock *Succ = Term->getSuccessor(i);
+        if (Succ != BB)
+          continue;
+
+        if (Visited.count(*PI)) {
+          // Normal forward edge
+          if (Term->isConditional()) {
+            // Try to treat it like an ELSE block
+            BasicBlock *Other = Term->getSuccessor(!i);
+            if (Visited.count(Other) && !Loops.count(Other) &&
+                !Pred.count(Other) && !Pred.count(*PI)) {
+
+              Pred[Other] = BoolFalse;
+              Pred[*PI] = BoolTrue;
+              continue;
+            }
+          }
+          Pred[*PI] = buildCondition(Term, i, false);
+
+        } else {
+          // Back edge
+          LPred[*PI] = buildCondition(Term, i, true);
+        }
+      }
+
+    } else {
+
+      // It's an exit from a sub region
+      while(R->getParent() != ParentRegion)
+        R = R->getParent();
+
+      // Edge from inside a subregion to its entry, ignore it
+      if (R == N)
+        continue;
+
+      BasicBlock *Entry = R->getEntry();
+      if (Visited.count(Entry))
+        Pred[Entry] = BoolTrue;
+      else
+        LPred[Entry] = BoolFalse;
+    }
+  }
+}
+
+/// \brief Collect various loop and predicate infos
+void StructurizeCFG::collectInfos() {
+  // Reset predicate
+  Predicates.clear();
+
+  // and loop infos
+  Loops.clear();
+  LoopPreds.clear();
+
+  // Reset the visited nodes
+  Visited.clear();
+
+  for (RNVector::reverse_iterator OI = Order.rbegin(), OE = Order.rend();
+       OI != OE; ++OI) {
+
+    // Analyze all the conditions leading to a node
+    gatherPredicates(*OI);
+
+    // Remember that we've seen this node
+    Visited.insert((*OI)->getEntry());
+
+    // Find the last back edges
+    analyzeLoops(*OI);
+  }
+}
+
+/// \brief Insert the missing branch conditions
+void StructurizeCFG::insertConditions(bool Loops) {
+  BranchVector &Conds = Loops ? LoopConds : Conditions;
+  Value *Default = Loops ? BoolTrue : BoolFalse;
+  SSAUpdater PhiInserter;
+
+  for (BranchVector::iterator I = Conds.begin(),
+       E = Conds.end(); I != E; ++I) {
+
+    BranchInst *Term = *I;
+    assert(Term->isConditional());
+
+    BasicBlock *Parent = Term->getParent();
+    BasicBlock *SuccTrue = Term->getSuccessor(0);
+    BasicBlock *SuccFalse = Term->getSuccessor(1);
+
+    PhiInserter.Initialize(Boolean, "");
+    PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
+    PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
+
+    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
+
+    NearestCommonDominator Dominator(DT);
+    Dominator.addBlock(Parent, false);
+
+    Value *ParentValue = 0;
+    for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
+         PI != PE; ++PI) {
+
+      if (PI->first == Parent) {
+        ParentValue = PI->second;
+        break;
+      }
+      PhiInserter.AddAvailableValue(PI->first, PI->second);
+      Dominator.addBlock(PI->first);
+    }
+
+    if (ParentValue) {
+      Term->setCondition(ParentValue);
+    } else {
+      if (!Dominator.wasResultExplicitMentioned())
+        PhiInserter.AddAvailableValue(Dominator.getResult(), Default);
+
+      Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
+    }
+  }
+}
+
+/// \brief Remove all PHI values coming from "From" into "To" and remember
+/// them in DeletedPhis
+void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
+  PhiMap &Map = DeletedPhis[To];
+  for (BasicBlock::iterator I = To->begin(), E = To->end();
+       I != E && isa<PHINode>(*I);) {
+
+    PHINode &Phi = cast<PHINode>(*I++);
+    while (Phi.getBasicBlockIndex(From) != -1) {
+      Value *Deleted = Phi.removeIncomingValue(From, false);
+      Map[&Phi].push_back(std::make_pair(From, Deleted));
+    }
+  }
+}
+
+/// \brief Add a dummy PHI value as soon as we knew the new predecessor
+void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
+  for (BasicBlock::iterator I = To->begin(), E = To->end();
+       I != E && isa<PHINode>(*I);) {
+
+    PHINode &Phi = cast<PHINode>(*I++);
+    Value *Undef = UndefValue::get(Phi.getType());
+    Phi.addIncoming(Undef, From);
+  }
+  AddedPhis[To].push_back(From);
+}
+
+/// \brief Add the real PHI value as soon as everything is set up
+void StructurizeCFG::setPhiValues() {
+  SSAUpdater Updater;
+  for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
+       AI != AE; ++AI) {
+
+    BasicBlock *To = AI->first;
+    BBVector &From = AI->second;
+
+    if (!DeletedPhis.count(To))
+      continue;
+
+    PhiMap &Map = DeletedPhis[To];
+    for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
+         PI != PE; ++PI) {
+
+      PHINode *Phi = PI->first;
+      Value *Undef = UndefValue::get(Phi->getType());
+      Updater.Initialize(Phi->getType(), "");
+      Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
+      Updater.AddAvailableValue(To, Undef);
+
+      NearestCommonDominator Dominator(DT);
+      Dominator.addBlock(To, false);
+      for (BBValueVector::iterator VI = PI->second.begin(),
+           VE = PI->second.end(); VI != VE; ++VI) {
+
+        Updater.AddAvailableValue(VI->first, VI->second);
+        Dominator.addBlock(VI->first);
+      }
+
+      if (!Dominator.wasResultExplicitMentioned())
+        Updater.AddAvailableValue(Dominator.getResult(), Undef);
+
+      for (BBVector::iterator FI = From.begin(), FE = From.end();
+           FI != FE; ++FI) {
+
+        int Idx = Phi->getBasicBlockIndex(*FI);
+        assert(Idx != -1);
+        Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
+      }
+    }
+
+    DeletedPhis.erase(To);
+  }
+  assert(DeletedPhis.empty());
+}
+
+/// \brief Remove phi values from all successors and then remove the terminator.
+void StructurizeCFG::killTerminator(BasicBlock *BB) {
+  TerminatorInst *Term = BB->getTerminator();
+  if (!Term)
+    return;
+
+  for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
+       SI != SE; ++SI) {
+
+    delPhiValues(BB, *SI);
+  }
+
+  Term->eraseFromParent();
+}
+
+/// \brief Let node exit(s) point to NewExit
+void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
+                                bool IncludeDominator) {
+  if (Node->isSubRegion()) {
+    Region *SubRegion = Node->getNodeAs<Region>();
+    BasicBlock *OldExit = SubRegion->getExit();
+    BasicBlock *Dominator = 0;
+
+    // Find all the edges from the sub region to the exit
+    for (pred_iterator I = pred_begin(OldExit), E = pred_end(OldExit);
+         I != E;) {
+
+      BasicBlock *BB = *I++;
+      if (!SubRegion->contains(BB))
+        continue;
+
+      // Modify the edges to point to the new exit
+      delPhiValues(BB, OldExit);
+      BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
+      addPhiValues(BB, NewExit);
+
+      // Find the new dominator (if requested)
+      if (IncludeDominator) {
+        if (!Dominator)
+          Dominator = BB;
+        else
+          Dominator = DT->findNearestCommonDominator(Dominator, BB);
+      }
+    }
+
+    // Change the dominator (if requested)
+    if (Dominator)
+      DT->changeImmediateDominator(NewExit, Dominator);
+
+    // Update the region info
+    SubRegion->replaceExit(NewExit);
+
+  } else {
+    BasicBlock *BB = Node->getNodeAs<BasicBlock>();
+    killTerminator(BB);
+    BranchInst::Create(NewExit, BB);
+    addPhiValues(BB, NewExit);
+    if (IncludeDominator)
+      DT->changeImmediateDominator(NewExit, BB);
+  }
+}
+
+/// \brief Create a new flow node and update dominator tree and region info
+BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
+  LLVMContext &Context = Func->getContext();
+  BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
+                       Order.back()->getEntry();
+  BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
+                                        Func, Insert);
+  DT->addNewBlock(Flow, Dominator);
+  ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
+  return Flow;
+}
+
+/// \brief Create a new or reuse the previous node as flow node
+BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
+  BasicBlock *Entry = PrevNode->getEntry();
+
+  if (!PrevNode->isSubRegion()) {
+    killTerminator(Entry);
+    if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
+      return Entry;
+
+  }
+
+  // create a new flow node
+  BasicBlock *Flow = getNextFlow(Entry);
+
+  // and wire it up
+  changeExit(PrevNode, Flow, true);
+  PrevNode = ParentRegion->getBBNode(Flow);
+  return Flow;
+}
+
+/// \brief Returns the region exit if possible, otherwise just a new flow node
+BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
+                                        bool ExitUseAllowed) {
+  if (Order.empty() && ExitUseAllowed) {
+    BasicBlock *Exit = ParentRegion->getExit();
+    DT->changeImmediateDominator(Exit, Flow);
+    addPhiValues(Flow, Exit);
+    return Exit;
+  }
+  return getNextFlow(Flow);
+}
+
+/// \brief Set the previous node
+void StructurizeCFG::setPrevNode(BasicBlock *BB) {
+  PrevNode =  ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB) : 0;
+}
+
+/// \brief Does BB dominate all the predicates of Node ?
+bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
+  BBPredicates &Preds = Predicates[Node->getEntry()];
+  for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
+       PI != PE; ++PI) {
+
+    if (!DT->dominates(BB, PI->first))
+      return false;
+  }
+  return true;
+}
+
+/// \brief Can we predict that this node will always be called?
+bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
+  BBPredicates &Preds = Predicates[Node->getEntry()];
+  bool Dominated = false;
+
+  // Regionentry is always true
+  if (PrevNode == 0)
+    return true;
+
+  for (BBPredicates::iterator I = Preds.begin(), E = Preds.end();
+       I != E; ++I) {
+
+    if (I->second != BoolTrue)
+      return false;
+
+    if (!Dominated && DT->dominates(I->first, PrevNode->getEntry()))
+      Dominated = true;
+  }
+
+  // TODO: The dominator check is too strict
+  return Dominated;
+}
+
+/// Take one node from the order vector and wire it up
+void StructurizeCFG::wireFlow(bool ExitUseAllowed,
+                              BasicBlock *LoopEnd) {
+  RegionNode *Node = Order.pop_back_val();
+  Visited.insert(Node->getEntry());
+
+  if (isPredictableTrue(Node)) {
+    // Just a linear flow
+    if (PrevNode) {
+      changeExit(PrevNode, Node->getEntry(), true);
+    }
+    PrevNode = Node;
+
+  } else {
+    // Insert extra prefix node (or reuse last one)
+    BasicBlock *Flow = needPrefix(false);
+
+    // Insert extra postfix node (or use exit instead)
+    BasicBlock *Entry = Node->getEntry();
+    BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
+
+    // let it point to entry and next block
+    Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
+    addPhiValues(Flow, Entry);
+    DT->changeImmediateDominator(Entry, Flow);
+
+    PrevNode = Node;
+    while (!Order.empty() && !Visited.count(LoopEnd) &&
+           dominatesPredicates(Entry, Order.back())) {
+      handleLoops(false, LoopEnd);
+    }
+
+    changeExit(PrevNode, Next, false);
+    setPrevNode(Next);
+  }
+}
+
+void StructurizeCFG::handleLoops(bool ExitUseAllowed,
+                                 BasicBlock *LoopEnd) {
+  RegionNode *Node = Order.back();
+  BasicBlock *LoopStart = Node->getEntry();
+
+  if (!Loops.count(LoopStart)) {
+    wireFlow(ExitUseAllowed, LoopEnd);
+    return;
+  }
+
+  if (!isPredictableTrue(Node))
+    LoopStart = needPrefix(true);
+
+  LoopEnd = Loops[Node->getEntry()];
+  wireFlow(false, LoopEnd);
+  while (!Visited.count(LoopEnd)) {
+    handleLoops(false, LoopEnd);
+  }
+
+  // Create an extra loop end node
+  LoopEnd = needPrefix(false);
+  BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
+  LoopConds.push_back(BranchInst::Create(Next, LoopStart,
+                                         BoolUndef, LoopEnd));
+  addPhiValues(LoopEnd, LoopStart);
+  setPrevNode(Next);
+}
+
+/// After this function control flow looks like it should be, but
+/// branches and PHI nodes only have undefined conditions.
+void StructurizeCFG::createFlow() {
+  BasicBlock *Exit = ParentRegion->getExit();
+  bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
+
+  DeletedPhis.clear();
+  AddedPhis.clear();
+  Conditions.clear();
+  LoopConds.clear();
+
+  PrevNode = 0;
+  Visited.clear();
+
+  while (!Order.empty()) {
+    handleLoops(EntryDominatesExit, 0);
+  }
+
+  if (PrevNode)
+    changeExit(PrevNode, Exit, EntryDominatesExit);
+  else
+    assert(EntryDominatesExit);
+}
+
+/// Handle a rare case where the disintegrated nodes instructions
+/// no longer dominate all their uses. Not sure if this is really nessasary
+void StructurizeCFG::rebuildSSA() {
+  SSAUpdater Updater;
+  for (Region::block_iterator I = ParentRegion->block_begin(),
+                              E = ParentRegion->block_end();
+       I != E; ++I) {
+
+    BasicBlock *BB = *I;
+    for (BasicBlock::iterator II = BB->begin(), IE = BB->end();
+         II != IE; ++II) {
+
+      bool Initialized = false;
+      for (Use *I = &II->use_begin().getUse(), *Next; I; I = Next) {
+
+        Next = I->getNext();
+
+        Instruction *User = cast<Instruction>(I->getUser());
+        if (User->getParent() == BB) {
+          continue;
+
+        } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
+          if (UserPN->getIncomingBlock(*I) == BB)
+            continue;
+        }
+
+        if (DT->dominates(II, User))
+          continue;
+
+        if (!Initialized) {
+          Value *Undef = UndefValue::get(II->getType());
+          Updater.Initialize(II->getType(), "");
+          Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
+          Updater.AddAvailableValue(BB, II);
+          Initialized = true;
+        }
+        Updater.RewriteUseAfterInsertions(*I);
+      }
+    }
+  }
+}
+
+/// \brief Run the transformation for each region found
+bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
+  if (R->isTopLevelRegion())
+    return false;
+
+  Func = R->getEntry()->getParent();
+  ParentRegion = R;
+
+  DT = &getAnalysis<DominatorTree>();
+
+  orderNodes();
+  collectInfos();
+  createFlow();
+  insertConditions(false);
+  insertConditions(true);
+  setPhiValues();
+  rebuildSSA();
+
+  // Cleanup
+  Order.clear();
+  Visited.clear();
+  DeletedPhis.clear();
+  AddedPhis.clear();
+  Predicates.clear();
+  Conditions.clear();
+  Loops.clear();
+  LoopPreds.clear();
+  LoopConds.clear();
+
+  return true;
+}
+
+/// \brief Create the pass
+Pass *llvm::createStructurizeCFGPass() {
+  return new StructurizeCFG();
+}