Delete the StrongPHIElimination pass, leaving only a shell.

The StrongPHIElimination pass did not work, and nobody has worked on it for two
years.

A rewrite is underway, so I am leaving this shell pass instead of deleting it
completely.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120830 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 1018 deletions

diff --git a/lib/CodeGen/StrongPHIElimination.cpp b/lib/CodeGen/StrongPHIElimination.cpp
index 0bf6f8e..0ecea6d 100644
--- a/lib/CodeGen/StrongPHIElimination.cpp
+++ b/lib/CodeGen/StrongPHIElimination.cpp
@@ -7,15 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This pass eliminates machine instruction PHI nodes by inserting copy
-// instructions, using an intelligent copy-folding technique based on
-// dominator information.  This is technique is derived from:
-// 
-//    Budimlic, et al. Fast copy coalescing and live-range identification.
-//    In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language
-//    Design and Implementation (Berlin, Germany, June 17 - 19, 2002).
-//    PLDI '02. ACM, New York, NY, 25-32.
-//    DOI= http://doi.acm.org/10.1145/512529.512534
 //
 //===----------------------------------------------------------------------===//
 
@@ -24,132 +15,33 @@
 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineInstr.h"
-#include "llvm/CodeGen/MachineInstrBuilder.h"
-#include "llvm/CodeGen/MachineLoopInfo.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/RegisterCoalescer.h"
-#include "llvm/Target/TargetInstrInfo.h"
-#include "llvm/Target/TargetMachine.h"
-#include "llvm/ADT/DepthFirstIterator.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
 using namespace llvm;
 
 namespace {
-  struct StrongPHIElimination : public MachineFunctionPass {
-    static char ID; // Pass identification, replacement for typeid
-    StrongPHIElimination() : MachineFunctionPass(ID) {
-      initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
-    }
-
-    // Waiting stores, for each MBB, the set of copies that need to
-    // be inserted into that MBB
-    DenseMap<MachineBasicBlock*,
-             std::multimap<unsigned, unsigned> > Waiting;
-    
-    // Stacks holds the renaming stack for each register
-    std::map<unsigned, std::vector<unsigned> > Stacks;
-    
-    // Registers in UsedByAnother are PHI nodes that are themselves
-    // used as operands to another PHI node
-    std::set<unsigned> UsedByAnother;
-    
-    // RenameSets are the is a map from a PHI-defined register
-    // to the input registers to be coalesced along with the 
-    // predecessor block for those input registers.
-    std::map<unsigned, std::map<unsigned, MachineBasicBlock*> > RenameSets;
-    
-    // PhiValueNumber holds the ID numbers of the VNs for each phi that we're
-    // eliminating, indexed by the register defined by that phi.
-    std::map<unsigned, unsigned> PhiValueNumber;
-
-    // Store the DFS-in number of each block
-    DenseMap<MachineBasicBlock*, unsigned> preorder;
-    
-    // Store the DFS-out number of each block
-    DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
-
-    bool runOnMachineFunction(MachineFunction &Fn);
-    
-    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-      AU.setPreservesCFG();
-      AU.addRequired<MachineDominatorTree>();
-      AU.addRequired<SlotIndexes>();
-      AU.addPreserved<SlotIndexes>();
-      AU.addRequired<LiveIntervals>();
-      
-      // TODO: Actually make this true.
-      AU.addPreserved<LiveIntervals>();
-      AU.addPreserved<RegisterCoalescer>();
-      MachineFunctionPass::getAnalysisUsage(AU);
-    }
-    
-    virtual void releaseMemory() {
-      preorder.clear();
-      maxpreorder.clear();
-      
-      Waiting.clear();
-      Stacks.clear();
-      UsedByAnother.clear();
-      RenameSets.clear();
-    }
+class StrongPHIElimination : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  StrongPHIElimination() : MachineFunctionPass(ID) {
+    initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
+  }
 
-  private:
-    
-    /// DomForestNode - Represents a node in the "dominator forest".  This is
-    /// a forest in which the nodes represent registers and the edges
-    /// represent a dominance relation in the block defining those registers.
-    struct DomForestNode {
-    private:
-      // Store references to our children
-      std::vector<DomForestNode*> children;
-      // The register we represent
-      unsigned reg;
-      
-      // Add another node as our child
-      void addChild(DomForestNode* DFN) { children.push_back(DFN); }
-      
-    public:
-      typedef std::vector<DomForestNode*>::iterator iterator;
-      
-      // Create a DomForestNode by providing the register it represents, and
-      // the node to be its parent.  The virtual root node has register 0
-      // and a null parent.
-      DomForestNode(unsigned r, DomForestNode* parent) : reg(r) {
-        if (parent)
-          parent->addChild(this);
-      }
-      
-      ~DomForestNode() {
-        for (iterator I = begin(), E = end(); I != E; ++I)
-          delete *I;
-      }
-      
-      /// getReg - Return the regiser that this node represents
-      inline unsigned getReg() { return reg; }
-      
-      // Provide iterator access to our children
-      inline DomForestNode::iterator begin() { return children.begin(); }
-      inline DomForestNode::iterator end() { return children.end(); }
-    };
-    
-    void computeDFS(MachineFunction& MF);
-    void processBlock(MachineBasicBlock* MBB);
+private:
+  bool runOnMachineFunction(MachineFunction &Fn) {
+    llvm_unreachable("Strong phi elimination is not implemented");
+  }
     
-    std::vector<DomForestNode*> computeDomForest(
-                           std::map<unsigned, MachineBasicBlock*>& instrs,
-                                                 MachineRegisterInfo& MRI);
-    void processPHIUnion(MachineInstr* Inst,
-                         std::map<unsigned, MachineBasicBlock*>& PHIUnion,
-                         std::vector<StrongPHIElimination::DomForestNode*>& DF,
-                         std::vector<std::pair<unsigned, unsigned> >& locals);
-    void ScheduleCopies(MachineBasicBlock* MBB, std::set<unsigned>& pushed);
-    void InsertCopies(MachineDomTreeNode* MBB,
-                      SmallPtrSet<MachineBasicBlock*, 16>& v);
-    bool mergeLiveIntervals(unsigned primary, unsigned secondary);
-  };
-}
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.setPreservesCFG();
+    AU.addRequired<MachineDominatorTree>();
+    AU.addRequired<SlotIndexes>();
+    AU.addPreserved<SlotIndexes>();
+    AU.addRequired<LiveIntervals>();
+    AU.addPreserved<LiveIntervals>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+} // namespace
 
 char StrongPHIElimination::ID = 0;
 INITIALIZE_PASS_BEGIN(StrongPHIElimination, "strong-phi-node-elimination",
@@ -162,891 +54,3 @@ INITIALIZE_PASS_END(StrongPHIElimination, "strong-phi-node-elimination",
 
 char &llvm::StrongPHIEliminationID = StrongPHIElimination::ID;
 
-/// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree
-/// of the given MachineFunction.  These numbers are then used in other parts
-/// of the PHI elimination process.
-void StrongPHIElimination::computeDFS(MachineFunction& MF) {
-  SmallPtrSet<MachineDomTreeNode*, 8> frontier;
-  SmallPtrSet<MachineDomTreeNode*, 8> visited;
-  
-  unsigned time = 0;
-  
-  MachineDominatorTree& DT = getAnalysis<MachineDominatorTree>();
-  
-  MachineDomTreeNode* node = DT.getRootNode();
-  
-  std::vector<MachineDomTreeNode*> worklist;
-  worklist.push_back(node);
-  
-  while (!worklist.empty()) {
-    MachineDomTreeNode* currNode = worklist.back();
-    
-    if (!frontier.count(currNode)) {
-      frontier.insert(currNode);
-      ++time;
-      preorder.insert(std::make_pair(currNode->getBlock(), time));
-    }
-    
-    bool inserted = false;
-    for (MachineDomTreeNode::iterator I = currNode->begin(), E = currNode->end();
-         I != E; ++I)
-      if (!frontier.count(*I) && !visited.count(*I)) {
-        worklist.push_back(*I);
-        inserted = true;
-        break;
-      }
-    
-    if (!inserted) {
-      frontier.erase(currNode);
-      visited.insert(currNode);
-      maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
-      
-      worklist.pop_back();
-    }
-  }
-}
-
-namespace {
-
-/// PreorderSorter - a helper class that is used to sort registers
-/// according to the preorder number of their defining blocks
-class PreorderSorter {
-private:
-  DenseMap<MachineBasicBlock*, unsigned>& preorder;
-  MachineRegisterInfo& MRI;
-  
-public:
-  PreorderSorter(DenseMap<MachineBasicBlock*, unsigned>& p,
-                MachineRegisterInfo& M) : preorder(p), MRI(M) { }
-  
-  bool operator()(unsigned A, unsigned B) {
-    if (A == B)
-      return false;
-    
-    MachineBasicBlock* ABlock = MRI.getVRegDef(A)->getParent();
-    MachineBasicBlock* BBlock = MRI.getVRegDef(B)->getParent();
-    
-    if (preorder[ABlock] < preorder[BBlock])
-      return true;
-    else if (preorder[ABlock] > preorder[BBlock])
-      return false;
-    
-    return false;
-  }
-};
-
-}
-
-/// computeDomForest - compute the subforest of the DomTree corresponding
-/// to the defining blocks of the registers in question
-std::vector<StrongPHIElimination::DomForestNode*>
-StrongPHIElimination::computeDomForest(
-                  std::map<unsigned, MachineBasicBlock*>& regs, 
-                                       MachineRegisterInfo& MRI) {
-  // Begin by creating a virtual root node, since the actual results
-  // may well be a forest.  Assume this node has maximum DFS-out number.
-  DomForestNode* VirtualRoot = new DomForestNode(0, 0);
-  maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL));
-  
-  // Populate a worklist with the registers
-  std::vector<unsigned> worklist;
-  worklist.reserve(regs.size());
-  for (std::map<unsigned, MachineBasicBlock*>::iterator I = regs.begin(),
-       E = regs.end(); I != E; ++I)
-    worklist.push_back(I->first);
-  
-  // Sort the registers by the DFS-in number of their defining block
-  PreorderSorter PS(preorder, MRI);
-  std::sort(worklist.begin(), worklist.end(), PS);
-  
-  // Create a "current parent" stack, and put the virtual root on top of it
-  DomForestNode* CurrentParent = VirtualRoot;
-  std::vector<DomForestNode*> stack;
-  stack.push_back(VirtualRoot);
-  
-  // Iterate over all the registers in the previously computed order
-  for (std::vector<unsigned>::iterator I = worklist.begin(), E = worklist.end();
-       I != E; ++I) {
-    unsigned pre = preorder[MRI.getVRegDef(*I)->getParent()];
-    MachineBasicBlock* parentBlock = CurrentParent->getReg() ?
-                 MRI.getVRegDef(CurrentParent->getReg())->getParent() :
-                 0;
-    
-    // If the DFS-in number of the register is greater than the DFS-out number
-    // of the current parent, repeatedly pop the parent stack until it isn't.
-    while (pre > maxpreorder[parentBlock]) {
-      stack.pop_back();
-      CurrentParent = stack.back();
-      
-      parentBlock = CurrentParent->getReg() ?
-                   MRI.getVRegDef(CurrentParent->getReg())->getParent() :
-                   0;
-    }
-    
-    // Now that we've found the appropriate parent, create a DomForestNode for
-    // this register and attach it to the forest
-    DomForestNode* child = new DomForestNode(*I, CurrentParent);
-    
-    // Push this new node on the "current parent" stack
-    stack.push_back(child);
-    CurrentParent = child;
-  }
-  
-  // Return a vector containing the children of the virtual root node
-  std::vector<DomForestNode*> ret;
-  ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end());
-  return ret;
-}
-
-/// isLiveIn - helper method that determines, from a regno, if a register
-/// is live into a block
-static bool isLiveIn(unsigned r, MachineBasicBlock* MBB,
-                     LiveIntervals& LI) {
-  LiveInterval& I = LI.getOrCreateInterval(r);
-  SlotIndex idx = LI.getMBBStartIdx(MBB);
-  return I.liveAt(idx);
-}
-
-/// isLiveOut - help method that determines, from a regno, if a register is
-/// live out of a block.
-static bool isLiveOut(unsigned r, MachineBasicBlock* MBB,
-                      LiveIntervals& LI) {
-  for (MachineBasicBlock::succ_iterator PI = MBB->succ_begin(),
-       E = MBB->succ_end(); PI != E; ++PI)
-    if (isLiveIn(r, *PI, LI))
-      return true;
-  
-  return false;
-}
-
-/// interferes - checks for local interferences by scanning a block.  The only
-/// trick parameter is 'mode' which tells it the relationship of the two
-/// registers. 0 - defined in the same block, 1 - first properly dominates
-/// second, 2 - second properly dominates first 
-static bool interferes(unsigned a, unsigned b, MachineBasicBlock* scan,
-                       LiveIntervals& LV, unsigned mode) {
-  MachineInstr* def = 0;
-  MachineInstr* kill = 0;
-  
-  // The code is still in SSA form at this point, so there is only one
-  // definition per VReg.  Thus we can safely use MRI->getVRegDef().
-  const MachineRegisterInfo* MRI = &scan->getParent()->getRegInfo();
-  
-  bool interference = false;
-  
-  // Wallk the block, checking for interferences
-  for (MachineBasicBlock::iterator MBI = scan->begin(), MBE = scan->end();
-       MBI != MBE; ++MBI) {
-    MachineInstr* curr = MBI;
-    
-    // Same defining block...
-    if (mode == 0) {
-      if (curr == MRI->getVRegDef(a)) {
-        // If we find our first definition, save it
-        if (!def) {
-          def = curr;
-        // If there's already an unkilled definition, then 
-        // this is an interference
-        } else if (!kill) {
-          interference = true;
-          break;
-        // If there's a definition followed by a KillInst, then
-        // they can't interfere
-        } else {
-          interference = false;
-          break;
-        }
-      // Symmetric with the above
-      } else if (curr == MRI->getVRegDef(b)) {
-        if (!def) {
-          def = curr;
-        } else if (!kill) {
-          interference = true;
-          break;
-        } else {
-          interference = false;
-          break;
-        }
-      // Store KillInsts if they match up with the definition
-      } else if (curr->killsRegister(a)) {
-        if (def == MRI->getVRegDef(a)) {
-          kill = curr;
-        } else if (curr->killsRegister(b)) {
-          if (def == MRI->getVRegDef(b)) {
-            kill = curr;
-          }
-        }
-      }
-    // First properly dominates second...
-    } else if (mode == 1) {
-      if (curr == MRI->getVRegDef(b)) {
-        // Definition of second without kill of first is an interference
-        if (!kill) {
-          interference = true;
-          break;
-        // Definition after a kill is a non-interference
-        } else {
-          interference = false;
-          break;
-        }
-      // Save KillInsts of First
-      } else if (curr->killsRegister(a)) {
-        kill = curr;
-      }
-    // Symmetric with the above
-    } else if (mode == 2) {
-      if (curr == MRI->getVRegDef(a)) {
-        if (!kill) {
-          interference = true;
-          break;
-        } else {
-          interference = false;
-          break;
-        }
-      } else if (curr->killsRegister(b)) {
-        kill = curr;
-      }
-    }
-  }
-  
-  return interference;
-}
-
-/// processBlock - Determine how to break up PHIs in the current block.  Each
-/// PHI is broken up by some combination of renaming its operands and inserting
-/// copies.  This method is responsible for determining which operands receive
-/// which treatment.
-void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
-  
-  // Holds names that have been added to a set in any PHI within this block
-  // before the current one.
-  std::set<unsigned> ProcessedNames;
-  
-  // Iterate over all the PHI nodes in this block
-  MachineBasicBlock::iterator P = MBB->begin();
-  while (P != MBB->end() && P->isPHI()) {
-    unsigned DestReg = P->getOperand(0).getReg();
-    
-    // Don't both doing PHI elimination for dead PHI's.
-    if (P->registerDefIsDead(DestReg)) {
-      ++P;
-      continue;
-    }
-
-    LiveInterval& PI = LI.getOrCreateInterval(DestReg);
-    SlotIndex pIdx = LI.getInstructionIndex(P).getDefIndex();
-    VNInfo* PVN = PI.getLiveRangeContaining(pIdx)->valno;
-    PhiValueNumber.insert(std::make_pair(DestReg, PVN->id));
-
-    // PHIUnion is the set of incoming registers to the PHI node that
-    // are going to be renames rather than having copies inserted.  This set
-    // is refinded over the course of this function.  UnionedBlocks is the set
-    // of corresponding MBBs.
-    std::map<unsigned, MachineBasicBlock*> PHIUnion;
-    SmallPtrSet<MachineBasicBlock*, 8> UnionedBlocks;
-  
-    // Iterate over the operands of the PHI node
-    for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
-      unsigned SrcReg = P->getOperand(i-1).getReg();
-      
-      // Don't need to try to coalesce a register with itself.
-      if (SrcReg == DestReg) {
-        ProcessedNames.insert(SrcReg);
-        continue;
-      }
-      
-      // We don't need to insert copies for implicit_defs.
-      MachineInstr* DefMI = MRI.getVRegDef(SrcReg);
-      if (DefMI->isImplicitDef())
-        ProcessedNames.insert(SrcReg);
-    
-      // Check for trivial interferences via liveness information, allowing us
-      // to avoid extra work later.  Any registers that interfere cannot both
-      // be in the renaming set, so choose one and add copies for it instead.
-      // The conditions are:
-      //   1) if the operand is live into the PHI node's block OR
-      //   2) if the PHI node is live out of the operand's defining block OR
-      //   3) if the operand is itself a PHI node and the original PHI is
-      //      live into the operand's defining block OR
-      //   4) if the operand is already being renamed for another PHI node
-      //      in this block OR
-      //   5) if any two operands are defined in the same block, insert copies
-      //      for one of them
-      if (isLiveIn(SrcReg, P->getParent(), LI) ||
-          isLiveOut(P->getOperand(0).getReg(),
-                    MRI.getVRegDef(SrcReg)->getParent(), LI) ||
-          ( MRI.getVRegDef(SrcReg)->isPHI() &&
-            isLiveIn(P->getOperand(0).getReg(),
-                     MRI.getVRegDef(SrcReg)->getParent(), LI) ) ||
-          ProcessedNames.count(SrcReg) ||
-          UnionedBlocks.count(MRI.getVRegDef(SrcReg)->getParent())) {
-        
-        // Add a copy for the selected register
-        MachineBasicBlock* From = P->getOperand(i).getMBB();
-        Waiting[From].insert(std::make_pair(SrcReg, DestReg));
-        UsedByAnother.insert(SrcReg);
-      } else {
-        // Otherwise, add it to the renaming set
-        PHIUnion.insert(std::make_pair(SrcReg,P->getOperand(i).getMBB()));
-        UnionedBlocks.insert(MRI.getVRegDef(SrcReg)->getParent());
-      }
-    }
-    
-    // Compute the dominator forest for the renaming set.  This is a forest
-    // where the nodes are the registers and the edges represent dominance 
-    // relations between the defining blocks of the registers
-    std::vector<StrongPHIElimination::DomForestNode*> DF = 
-                                                computeDomForest(PHIUnion, MRI);
-    
-    // Walk DomForest to resolve interferences at an inter-block level.  This
-    // will remove registers from the renaming set (and insert copies for them)
-    // if interferences are found.
-    std::vector<std::pair<unsigned, unsigned> > localInterferences;
-    processPHIUnion(P, PHIUnion, DF, localInterferences);
-    
-    // If one of the inputs is defined in the same block as the current PHI
-    // then we need to check for a local interference between that input and
-    // the PHI.
-    for (std::map<unsigned, MachineBasicBlock*>::iterator I = PHIUnion.begin(),
-         E = PHIUnion.end(); I != E; ++I)
-      if (MRI.getVRegDef(I->first)->getParent() == P->getParent())
-        localInterferences.push_back(std::make_pair(I->first,
-                                                    P->getOperand(0).getReg()));
-    
-    // The dominator forest walk may have returned some register pairs whose
-    // interference cannot be determined from dominator analysis.  We now 
-    // examine these pairs for local interferences.
-    for (std::vector<std::pair<unsigned, unsigned> >::iterator I =
-        localInterferences.begin(), E = localInterferences.end(); I != E; ++I) {
-      std::pair<unsigned, unsigned> p = *I;
-      
-      MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
-      
-      // Determine the block we need to scan and the relationship between
-      // the two registers
-      MachineBasicBlock* scan = 0;
-      unsigned mode = 0;
-      if (MRI.getVRegDef(p.first)->getParent() ==
-          MRI.getVRegDef(p.second)->getParent()) {
-        scan = MRI.getVRegDef(p.first)->getParent();
-        mode = 0; // Same block
-      } else if (MDT.dominates(MRI.getVRegDef(p.first)->getParent(),
-                               MRI.getVRegDef(p.second)->getParent())) {
-        scan = MRI.getVRegDef(p.second)->getParent();
-        mode = 1; // First dominates second
-      } else {
-        scan = MRI.getVRegDef(p.first)->getParent();
-        mode = 2; // Second dominates first
-      }
-      
-      // If there's an interference, we need to insert  copies
-      if (interferes(p.first, p.second, scan, LI, mode)) {
-        // Insert copies for First
-        for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
-          if (P->getOperand(i-1).getReg() == p.first) {
-            unsigned SrcReg = p.first;
-            MachineBasicBlock* From = P->getOperand(i).getMBB();
-            
-            Waiting[From].insert(std::make_pair(SrcReg,
-                                                P->getOperand(0).getReg()));
-            UsedByAnother.insert(SrcReg);
-            
-            PHIUnion.erase(SrcReg);
-          }
-        }
-      }
-    }
-    
-    // Add the renaming set for this PHI node to our overall renaming information
-    for (std::map<unsigned, MachineBasicBlock*>::iterator QI = PHIUnion.begin(),
-         QE = PHIUnion.end(); QI != QE; ++QI) {
-      DEBUG(dbgs() << "Adding Renaming: " << QI->first << " -> "
-                   << P->getOperand(0).getReg() << "\n");
-    }
-    
-    RenameSets.insert(std::make_pair(P->getOperand(0).getReg(), PHIUnion));
-    
-    // Remember which registers are already renamed, so that we don't try to 
-    // rename them for another PHI node in this block
-    for (std::map<unsigned, MachineBasicBlock*>::iterator I = PHIUnion.begin(),
-         E = PHIUnion.end(); I != E; ++I)
-      ProcessedNames.insert(I->first);
-    
-    ++P;
-  }
-}
-
-/// processPHIUnion - Take a set of candidate registers to be coalesced when
-/// decomposing the PHI instruction.  Use the DominanceForest to remove the ones
-/// that are known to interfere, and flag others that need to be checked for
-/// local interferences.
-void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
-                        std::map<unsigned, MachineBasicBlock*>& PHIUnion,
-                        std::vector<StrongPHIElimination::DomForestNode*>& DF,
-                        std::vector<std::pair<unsigned, unsigned> >& locals) {
-  
-  std::vector<DomForestNode*> worklist(DF.begin(), DF.end());
-  SmallPtrSet<DomForestNode*, 4> visited;
-  
-  // Code is still in SSA form, so we can use MRI::getVRegDef()
-  MachineRegisterInfo& MRI = Inst->getParent()->getParent()->getRegInfo();
-  
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  unsigned DestReg = Inst->getOperand(0).getReg();
-  
-  // DF walk on the DomForest
-  while (!worklist.empty()) {
-    DomForestNode* DFNode = worklist.back();
-    
-    visited.insert(DFNode);
-    
-    bool inserted = false;
-    for (DomForestNode::iterator CI = DFNode->begin(), CE = DFNode->end();
-         CI != CE; ++CI) {
-      DomForestNode* child = *CI;   
-      
-      // If the current node is live-out of the defining block of one of its
-      // children, insert a copy for it.  NOTE: The paper actually calls for
-      // a more elaborate heuristic for determining whether to insert copies
-      // for the child or the parent.  In the interest of simplicity, we're
-      // just always choosing the parent.
-      if (isLiveOut(DFNode->getReg(),
-          MRI.getVRegDef(child->getReg())->getParent(), LI)) {
-        // Insert copies for parent
-        for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
-          if (Inst->getOperand(i-1).getReg() == DFNode->getReg()) {
-            unsigned SrcReg = DFNode->getReg();
-            MachineBasicBlock* From = Inst->getOperand(i).getMBB();
-            
-            Waiting[From].insert(std::make_pair(SrcReg, DestReg));
-            UsedByAnother.insert(SrcReg);
-            
-            PHIUnion.erase(SrcReg);
-          }
-        }
-      
-      // If a node is live-in to the defining block of one of its children, but
-      // not live-out, then we need to scan that block for local interferences.
-      } else if (isLiveIn(DFNode->getReg(),
-                          MRI.getVRegDef(child->getReg())->getParent(), LI) ||
-                 MRI.getVRegDef(DFNode->getReg())->getParent() ==
-                                 MRI.getVRegDef(child->getReg())->getParent()) {
-        // Add (p, c) to possible local interferences
-        locals.push_back(std::make_pair(DFNode->getReg(), child->getReg()));
-      }
-      
-      if (!visited.count(child)) {
-        worklist.push_back(child);
-        inserted = true;
-      }
-    }
-    
-    if (!inserted) worklist.pop_back();
-  }
-}
-
-/// ScheduleCopies - Insert copies into predecessor blocks, scheduling
-/// them properly so as to avoid the 'lost copy' and the 'virtual swap'
-/// problems.
-///
-/// Based on "Practical Improvements to the Construction and Destruction
-/// of Static Single Assignment Form" by Briggs, et al.
-void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB,
-                                          std::set<unsigned>& pushed) {
-  // FIXME: This function needs to update LiveIntervals
-  std::multimap<unsigned, unsigned>& copy_set= Waiting[MBB];
-  
-  std::multimap<unsigned, unsigned> worklist;
-  std::map<unsigned, unsigned> map;
-  
-  // Setup worklist of initial copies
-  for (std::multimap<unsigned, unsigned>::iterator I = copy_set.begin(),
-       E = copy_set.end(); I != E; ) {
-    map.insert(std::make_pair(I->first, I->first));
-    map.insert(std::make_pair(I->second, I->second));
-         
-    if (!UsedByAnother.count(I->second)) {
-      worklist.insert(*I);
-      
-      // Avoid iterator invalidation
-      std::multimap<unsigned, unsigned>::iterator OI = I;
-      ++I;
-      copy_set.erase(OI);
-    } else {
-      ++I;
-    }
-  }
-  
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  MachineFunction* MF = MBB->getParent();
-  MachineRegisterInfo& MRI = MF->getRegInfo();
-  const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
-  
-  SmallVector<std::pair<unsigned, MachineInstr*>, 4> InsertedPHIDests;
-  
-  // Iterate over the worklist, inserting copies
-  while (!worklist.empty() || !copy_set.empty()) {
-    while (!worklist.empty()) {
-      std::multimap<unsigned, unsigned>::iterator WI = worklist.begin();
-      std::pair<unsigned, unsigned> curr = *WI;
-      worklist.erase(WI);
-      
-      const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
-      
-      if (isLiveOut(curr.second, MBB, LI)) {
-        // Create a temporary
-        unsigned t = MF->getRegInfo().createVirtualRegister(RC);
-        
-        // Insert copy from curr.second to a temporary at
-        // the Phi defining curr.second
-        MachineBasicBlock::iterator PI = MRI.getVRegDef(curr.second);
-        BuildMI(*PI->getParent(), PI, DebugLoc(), TII->get(TargetOpcode::COPY),
-                t).addReg(curr.second);
-        DEBUG(dbgs() << "Inserted copy from " << curr.second << " to " << t
-                     << "\n");
-        
-        // Push temporary on Stacks
-        Stacks[curr.second].push_back(t);
-        
-        // Insert curr.second in pushed
-        pushed.insert(curr.second);
-        
-        // Create a live interval for this temporary
-        InsertedPHIDests.push_back(std::make_pair(t, --PI));
-      }
-      
-      // Insert copy from map[curr.first] to curr.second
-      BuildMI(*MBB, MBB->getFirstTerminator(), DebugLoc(),
-             TII->get(TargetOpcode::COPY), curr.second).addReg(map[curr.first]);
-      map[curr.first] = curr.second;
-      DEBUG(dbgs() << "Inserted copy from " << curr.first << " to "
-                   << curr.second << "\n");
-      
-      // Push this copy onto InsertedPHICopies so we can
-      // update LiveIntervals with it.
-      MachineBasicBlock::iterator MI = MBB->getFirstTerminator();
-      InsertedPHIDests.push_back(std::make_pair(curr.second, --MI));
-      
-      // If curr.first is a destination in copy_set...
-      for (std::multimap<unsigned, unsigned>::iterator I = copy_set.begin(),
-           E = copy_set.end(); I != E; )
-        if (curr.first == I->second) {
-          std::pair<unsigned, unsigned> temp = *I;
-          worklist.insert(temp);
-          
-          // Avoid iterator invalidation
-          std::multimap<unsigned, unsigned>::iterator OI = I;
-          ++I;
-          copy_set.erase(OI);
-          
-          break;
-        } else {
-          ++I;
-        }
-    }
-    
-    if (!copy_set.empty()) {
-      std::multimap<unsigned, unsigned>::iterator CI = copy_set.begin();
-      std::pair<unsigned, unsigned> curr = *CI;
-      worklist.insert(curr);
-      copy_set.erase(CI);
-      
-      LiveInterval& I = LI.getInterval(curr.second);
-      MachineBasicBlock::iterator term = MBB->getFirstTerminator();
-      SlotIndex endIdx = SlotIndex();
-      if (term != MBB->end())
-        endIdx = LI.getInstructionIndex(term);
-      else
-        endIdx = LI.getMBBEndIdx(MBB);
-      
-      if (I.liveAt(endIdx)) {
-        const TargetRegisterClass *RC =
-                                       MF->getRegInfo().getRegClass(curr.first);
-        
-        // Insert a copy from dest to a new temporary t at the end of b
-        unsigned t = MF->getRegInfo().createVirtualRegister(RC);
-        BuildMI(*MBB, MBB->getFirstTerminator(), DebugLoc(),
-                TII->get(TargetOpcode::COPY), t).addReg(curr.second);
-        map[curr.second] = t;
-        
-        MachineBasicBlock::iterator TI = MBB->getFirstTerminator();
-        InsertedPHIDests.push_back(std::make_pair(t, --TI));
-      }
-    }
-  }
-  
-  // Renumber the instructions so that we can perform the index computations
-  // needed to create new live intervals.
-  LI.renumber();
-  
-  // For copies that we inserted at the ends of predecessors, we construct
-  // live intervals.  This is pretty easy, since we know that the destination
-  // register cannot have be in live at that point previously.  We just have
-  // to make sure that, for registers that serve as inputs to more than one
-  // PHI, we don't create multiple overlapping live intervals.
-  std::set<unsigned> RegHandled;
-  for (SmallVector<std::pair<unsigned, MachineInstr*>, 4>::iterator I =
-       InsertedPHIDests.begin(), E = InsertedPHIDests.end(); I != E; ++I) {
-    if (RegHandled.insert(I->first).second) {
-      LiveInterval& Int = LI.getOrCreateInterval(I->first);
-      SlotIndex instrIdx = LI.getInstructionIndex(I->second);
-      if (Int.liveAt(instrIdx.getDefIndex()))
-        Int.removeRange(instrIdx.getDefIndex(),
-                        LI.getMBBEndIdx(I->second->getParent()).getNextSlot(),
-                        true);
-      
-      LiveRange R = LI.addLiveRangeToEndOfBlock(I->first, I->second);
-      R.valno->setCopy(I->second);
-      R.valno->def = LI.getInstructionIndex(I->second).getDefIndex();
-    }
-  }
-}
-
-/// InsertCopies - insert copies into MBB and all of its successors
-void StrongPHIElimination::InsertCopies(MachineDomTreeNode* MDTN,
-                                 SmallPtrSet<MachineBasicBlock*, 16>& visited) {
-  MachineBasicBlock* MBB = MDTN->getBlock();
-  visited.insert(MBB);
-  
-  std::set<unsigned> pushed;
-  
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  // Rewrite register uses from Stacks
-  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
-      I != E; ++I) {
-    if (I->isPHI())
-      continue;
-    
-    for (unsigned i = 0; i < I->getNumOperands(); ++i)
-      if (I->getOperand(i).isReg() &&
-          Stacks[I->getOperand(i).getReg()].size()) {
-        // Remove the live range for the old vreg.
-        LiveInterval& OldInt = LI.getInterval(I->getOperand(i).getReg());
-        LiveInterval::iterator OldLR =
-          OldInt.FindLiveRangeContaining(LI.getInstructionIndex(I).getUseIndex());
-        if (OldLR != OldInt.end())
-          OldInt.removeRange(*OldLR, true);
-        
-        // Change the register
-        I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back());
-        
-        // Add a live range for the new vreg
-        LiveInterval& Int = LI.getInterval(I->getOperand(i).getReg());
-        VNInfo* FirstVN = *Int.vni_begin();
-        FirstVN->setHasPHIKill(false);
-        LiveRange LR (LI.getMBBStartIdx(I->getParent()),
-                      LI.getInstructionIndex(I).getUseIndex().getNextSlot(),
-                      FirstVN);
-        
-        Int.addRange(LR);
-      }
-  }    
-  
-  // Schedule the copies for this block
-  ScheduleCopies(MBB, pushed);
-  
-  // Recur down the dominator tree.
-  for (MachineDomTreeNode::iterator I = MDTN->begin(),
-       E = MDTN->end(); I != E; ++I)
-    if (!visited.count((*I)->getBlock()))
-      InsertCopies(*I, visited);
-  
-  // As we exit this block, pop the names we pushed while processing it
-  for (std::set<unsigned>::iterator I = pushed.begin(), 
-       E = pushed.end(); I != E; ++I)
-    Stacks[*I].pop_back();
-}
-
-bool StrongPHIElimination::mergeLiveIntervals(unsigned primary,
-                                              unsigned secondary) {
-  
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  LiveInterval& LHS = LI.getOrCreateInterval(primary);
-  LiveInterval& RHS = LI.getOrCreateInterval(secondary);
-  
-  LI.renumber();
-  
-  DenseMap<VNInfo*, VNInfo*> VNMap;
-  for (LiveInterval::iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
-    LiveRange R = *I;
- 
-    SlotIndex Start = R.start;
-    SlotIndex End = R.end;
-    if (LHS.getLiveRangeContaining(Start))
-      return false;
-    
-    if (LHS.getLiveRangeContaining(End))
-      return false;
-    
-    LiveInterval::iterator RI = std::upper_bound(LHS.begin(), LHS.end(), R);
-    if (RI != LHS.end() && RI->start < End)
-      return false;
-  }
-  
-  for (LiveInterval::iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
-    LiveRange R = *I;
-    VNInfo* OldVN = R.valno;
-    VNInfo*& NewVN = VNMap[OldVN];
-    if (!NewVN) {
-      NewVN = LHS.createValueCopy(OldVN, LI.getVNInfoAllocator());
-    }
-    
-    LiveRange LR (R.start, R.end, NewVN);
-    LHS.addRange(LR);
-  }
-  
-  LI.removeInterval(RHS.reg);
-  
-  return true;
-}
-
-bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
-  LiveIntervals& LI = getAnalysis<LiveIntervals>();
-  
-  // Compute DFS numbers of each block
-  computeDFS(Fn);
-  
-  // Determine which phi node operands need copies
-  for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
-    if (!I->empty() && I->begin()->isPHI())
-      processBlock(I);
-  
-  // Break interferences where two different phis want to coalesce
-  // in the same register.
-  std::set<unsigned> seen;
-  typedef std::map<unsigned, std::map<unsigned, MachineBasicBlock*> >
-          RenameSetType;
-  for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
-       I != E; ++I) {
-    for (std::map<unsigned, MachineBasicBlock*>::iterator
-         OI = I->second.begin(), OE = I->second.end(); OI != OE; ) {
-      if (!seen.count(OI->first)) {
-        seen.insert(OI->first);
-        ++OI;
-      } else {
-        Waiting[OI->second].insert(std::make_pair(OI->first, I->first));
-        unsigned reg = OI->first;
-        ++OI;
-        I->second.erase(reg);
-        DEBUG(dbgs() << "Removing Renaming: " << reg << " -> " << I->first
-                     << "\n");
-      }
-    }
-  }
-  
-  // Insert copies
-  // FIXME: This process should probably preserve LiveIntervals
-  SmallPtrSet<MachineBasicBlock*, 16> visited;
-  MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
-  InsertCopies(MDT.getRootNode(), visited);
-  
-  // Perform renaming
-  for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
-       I != E; ++I)
-    while (I->second.size()) {
-      std::map<unsigned, MachineBasicBlock*>::iterator SI = I->second.begin();
-      
-      DEBUG(dbgs() << "Renaming: " << SI->first << " -> " << I->first << "\n");
-      
-      if (SI->first != I->first) {
-        if (mergeLiveIntervals(I->first, SI->first)) {
-          Fn.getRegInfo().replaceRegWith(SI->first, I->first);
-      
-          if (RenameSets.count(SI->first)) {
-            I->second.insert(RenameSets[SI->first].begin(),
-                             RenameSets[SI->first].end());
-            RenameSets.erase(SI->first);
-          }
-        } else {
-          // Insert a last-minute copy if a conflict was detected.
-          const TargetInstrInfo *TII = Fn.getTarget().getInstrInfo();
-          BuildMI(*SI->second, SI->second->getFirstTerminator(), DebugLoc(),
-                  TII->get(TargetOpcode::COPY), I->first).addReg(SI->first);
-          
-          LI.renumber();
-          
-          LiveInterval& Int = LI.getOrCreateInterval(I->first);
-          SlotIndex instrIdx =
-                     LI.getInstructionIndex(--SI->second->getFirstTerminator());
-          if (Int.liveAt(instrIdx.getDefIndex()))
-            Int.removeRange(instrIdx.getDefIndex(),
-                            LI.getMBBEndIdx(SI->second).getNextSlot(), true);
-
-          LiveRange R = LI.addLiveRangeToEndOfBlock(I->first,
-                                            --SI->second->getFirstTerminator());
-          R.valno->setCopy(--SI->second->getFirstTerminator());
-          R.valno->def = instrIdx.getDefIndex();
-          
-          DEBUG(dbgs() << "Renaming failed: " << SI->first << " -> "
-                       << I->first << "\n");
-        }
-      }
-      
-      LiveInterval& Int = LI.getOrCreateInterval(I->first);
-      const LiveRange* LR =
-                       Int.getLiveRangeContaining(LI.getMBBEndIdx(SI->second));
-      LR->valno->setHasPHIKill(true);
-      
-      I->second.erase(SI->first);
-    }
-  
-  // Remove PHIs
-  std::vector<MachineInstr*> phis;
-  for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
-    for (MachineBasicBlock::iterator BI = I->begin(), BE = I->end();
-         BI != BE; ++BI)
-      if (BI->isPHI())
-        phis.push_back(BI);
-  }
-  
-  for (std::vector<MachineInstr*>::iterator I = phis.begin(), E = phis.end();
-       I != E; ) {
-    MachineInstr* PInstr = *(I++);
-    
-    // If this is a dead PHI node, then remove it from LiveIntervals.
-    unsigned DestReg = PInstr->getOperand(0).getReg();
-    LiveInterval& PI = LI.getInterval(DestReg);
-    if (PInstr->registerDefIsDead(DestReg)) {
-      if (PI.containsOneValue()) {
-        LI.removeInterval(DestReg);
-      } else {
-        SlotIndex idx = LI.getInstructionIndex(PInstr).getDefIndex();
-        PI.removeRange(*PI.getLiveRangeContaining(idx), true);
-      }
-    } else {
-      // Trim live intervals of input registers.  They are no longer live into
-      // this block if they died after the PHI.  If they lived after it, don't
-      // trim them because they might have other legitimate uses.
-      for (unsigned i = 1; i < PInstr->getNumOperands(); i += 2) {
-        unsigned reg = PInstr->getOperand(i).getReg();
-        
-        MachineBasicBlock* MBB = PInstr->getOperand(i+1).getMBB();
-        LiveInterval& InputI = LI.getInterval(reg);
-        if (MBB != PInstr->getParent() &&
-            InputI.liveAt(LI.getMBBStartIdx(PInstr->getParent())) &&
-            InputI.expiredAt(LI.getInstructionIndex(PInstr).getNextIndex()))
-          InputI.removeRange(LI.getMBBStartIdx(PInstr->getParent()),
-                             LI.getInstructionIndex(PInstr),
-                             true);
-      }
-      
-      // If the PHI is not dead, then the valno defined by the PHI
-      // now has an unknown def.
-      SlotIndex idx = LI.getInstructionIndex(PInstr).getDefIndex();
-      const LiveRange* PLR = PI.getLiveRangeContaining(idx);
-      PLR->valno->setIsPHIDef(true);
-      LiveRange R (LI.getMBBStartIdx(PInstr->getParent()),
-                   PLR->start, PLR->valno);
-      PI.addRange(R);
-    }
-    
-    LI.RemoveMachineInstrFromMaps(PInstr);
-    PInstr->eraseFromParent();
-  }
-  
-  LI.renumber();
-  
-  return true;
-}