Big PBQP allocator update. Adds coalescing support, stack slot coloring, several bug-fixes.

llvm-svn: 59414

llvm/lib/CodeGen/RegAllocPBQP.cpp

@@ -32,20 +32,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-// TODO:
-// 
-// * Use of std::set in constructPBQPProblem destroys allocation order preference.
-// Switch to an order preserving container.
-// 
-// * Coalescing support.
-
 #define DEBUG_TYPE "regalloc"
 
 #include "PBQP.h"
 #include "VirtRegMap.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/RegAllocRegistry.h"
+#include "llvm/CodeGen/RegisterCoalescer.h"
 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
+#include "llvm/CodeGen/LiveStackAnalysis.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/Target/TargetMachine.h"
@@ -63,7 +58,6 @@ static RegisterRegAlloc
 registerPBQPRepAlloc("pbqp", "PBQP register allocator",
                      createPBQPRegisterAllocator);
 
-
 namespace {
 
   //!
@@ -86,7 +80,11 @@ namespace {
     //! PBQP analysis usage.
     virtual void getAnalysisUsage(AnalysisUsage &au) const {
       au.addRequired<LiveIntervals>();
+      au.addRequiredTransitive<RegisterCoalescer>();
+      au.addRequired<LiveStacks>();
+      au.addPreserved<LiveStacks>();
       au.addRequired<MachineLoopInfo>();
+      au.addPreserved<MachineLoopInfo>();
       MachineFunctionPass::getAnalysisUsage(au);
     }
 
@@ -98,7 +96,11 @@ namespace {
     typedef std::vector<const LiveInterval*> Node2LIMap;
     typedef std::vector<unsigned> AllowedSet;
     typedef std::vector<AllowedSet> AllowedSetMap;
-    typedef std::set<unsigned> IgnoreSet;
+    typedef std::set<unsigned> RegSet;
+    typedef std::pair<unsigned, unsigned> RegPair;
+    typedef std::map<RegPair, PBQPNum> CoalesceMap;
+
+    typedef std::set<LiveInterval*> LiveIntervalSet;
 
     MachineFunction *mf;
     const TargetMachine *tm;
@@ -107,17 +109,22 @@ namespace {
     const MachineLoopInfo *loopInfo;
     MachineRegisterInfo *mri;
 
-    LiveIntervals *li;
+    LiveIntervals *lis;
+    LiveStacks *lss;
     VirtRegMap *vrm;
 
     LI2NodeMap li2Node;
     Node2LIMap node2LI;
     AllowedSetMap allowedSets;
-    IgnoreSet ignoreSet;
+    LiveIntervalSet vregIntervalsToAlloc,
+                    emptyVRegIntervals;
 
+    
     //! Builds a PBQP cost vector.
-    template <typename Container>
+    template <typename RegContainer>
-    PBQPVector* buildCostVector(const Container &allowed,
+    PBQPVector* buildCostVector(unsigned vReg,
+                                const RegContainer &allowed,
+                                const CoalesceMap &cealesces,
                                 PBQPNum spillCost) const;
 
     //! \brief Builds a PBQP interference matrix.
@@ -128,29 +135,28 @@ namespace {
     //! Expects allowed sets for two interfering LiveIntervals. These allowed
     //! sets should contain only allocable registers from the LiveInterval's
     //! register class, with any interfering pre-colored registers removed.
-    template <typename Container>
+    template <typename RegContainer>
-    PBQPMatrix* buildInterferenceMatrix(const Container &allowed1,
+    PBQPMatrix* buildInterferenceMatrix(const RegContainer &allowed1,
-                                        const Container &allowed2) const;
+                                        const RegContainer &allowed2) const;
 
     //!
     //! Expects allowed sets for two potentially coalescable LiveIntervals,
     //! and an estimated benefit due to coalescing. The allowed sets should
     //! contain only allocable registers from the LiveInterval's register
     //! classes, with any interfering pre-colored registers removed.
-    template <typename Container>
+    template <typename RegContainer>
-    PBQPMatrix* buildCoalescingMatrix(const Container &allowed1,
+    PBQPMatrix* buildCoalescingMatrix(const RegContainer &allowed1,
-                                      const Container &allowed2,
+                                      const RegContainer &allowed2,
                                       PBQPNum cBenefit) const;
 
-    //! \brief Helper function for constructInitialPBQPProblem().
+    //! \brief Finds coalescing opportunities and returns them as a map.
     //!
-    //! This function iterates over the Function we are about to allocate for
+    //! Any entries in the map are guaranteed coalescable, even if their
-    //! and computes spill costs.
+    //! corresponding live intervals overlap.
-    void calcSpillCosts();
+    CoalesceMap findCoalesces();
 
-    //! \brief Scans the MachineFunction being allocated to find coalescing
+    //! \brief Finds the initial set of vreg intervals to allocate.
-    //  opportunities.
+    void findVRegIntervalsToAlloc();
-    void findCoalescingOpportunities();
 
     //! \brief Constructs a PBQP problem representation of the register
     //! allocation problem for this function.
@@ -158,33 +164,64 @@ namespace {
     //! @return a PBQP solver object for the register allocation problem.
     pbqp* constructPBQPProblem();
 
+    //! \brief Adds a stack interval if the given live interval has been
+    //! spilled. Used to support stack slot coloring.
+    void addStackInterval(const LiveInterval *spilled, float &weight);
+
     //! \brief Given a solved PBQP problem maps this solution back to a register
     //! assignment.
     bool mapPBQPToRegAlloc(pbqp *problem); 
 
+    //! \brief Postprocessing before final spilling. Sets basic block "live in"
+    //! variables.
+    void finalizeAlloc() const;
+
   };
 
   char PBQPRegAlloc::ID = 0;
 }
 
 
-template <typename Container>
+template <typename RegContainer>
-PBQPVector* PBQPRegAlloc::buildCostVector(const Container &allowed,
+PBQPVector* PBQPRegAlloc::buildCostVector(unsigned vReg,
+                                          const RegContainer &allowed,
+                                          const CoalesceMap &coalesces,
                                           PBQPNum spillCost) const {
 
+  typedef typename RegContainer::const_iterator AllowedItr;
+
   // Allocate vector. Additional element (0th) used for spill option
   PBQPVector *v = new PBQPVector(allowed.size() + 1);
 
   (*v)[0] = spillCost;
 
+  // Iterate over the allowed registers inserting coalesce benefits if there
+  // are any.
+  unsigned ai = 0;
+  for (AllowedItr itr = allowed.begin(), end = allowed.end();
+       itr != end; ++itr, ++ai) {
+
+    unsigned pReg = *itr;
+
+    CoalesceMap::const_iterator cmItr =
+      coalesces.find(RegPair(vReg, pReg));
+
+    // No coalesce - on to the next preg.
+    if (cmItr == coalesces.end())
+      continue;
+   
+    // We have a coalesce - insert the benefit. 
+    (*v)[ai + 1] = -cmItr->second;  
+  }
+
   return v;
 }
 
-template <typename Container>
+template <typename RegContainer>
 PBQPMatrix* PBQPRegAlloc::buildInterferenceMatrix(
-      const Container &allowed1, const Container &allowed2) const {
+      const RegContainer &allowed1, const RegContainer &allowed2) const {
 
-  typedef typename Container::const_iterator ContainerIterator;
+  typedef typename RegContainer::const_iterator RegContainerIterator;
 
   // Construct a PBQP matrix representing the cost of allocation options. The
   // rows and columns correspond to the allocation options for the two live
@@ -210,14 +247,14 @@ PBQPMatrix* PBQPRegAlloc::buildInterferenceMatrix(
   unsigned ri = 1; 
 
   // Iterate over allowed sets, insert infinities where required. 
-  for (ContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end();
+  for (RegContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end();
        a1Itr != a1End; ++a1Itr) {
 
     // Column index, starts at 1 as for row index.
     unsigned ci = 1;
     unsigned reg1 = *a1Itr;
 
-    for (ContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end();
+    for (RegContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end();
          a2Itr != a2End; ++a2Itr) {
 
       unsigned reg2 = *a2Itr;
@@ -245,100 +282,262 @@ PBQPMatrix* PBQPRegAlloc::buildInterferenceMatrix(
   return m;
 }
 
-void PBQPRegAlloc::calcSpillCosts() {
+template <typename RegContainer>
+PBQPMatrix* PBQPRegAlloc::buildCoalescingMatrix(
+      const RegContainer &allowed1, const RegContainer &allowed2,
+      PBQPNum cBenefit) const {
 
-  // Calculate the spill cost for each live interval by iterating over the
+  typedef typename RegContainer::const_iterator RegContainerIterator;
-  // function counting loads and stores, with loop depth taken into account.
+
-  for (MachineFunction::const_iterator bbItr = mf->begin(), bbEnd = mf->end();
+  // Construct a PBQP Matrix representing the benefits of coalescing. As with
+  // interference matrices the rows and columns represent allowed registers
+  // for the LiveIntervals which are (potentially) to be coalesced. The amount
+  // -cBenefit will be placed in any element representing the same register
+  // for both intervals.
+  PBQPMatrix *m = new PBQPMatrix(allowed1.size() + 1, allowed2.size() + 1);
+
+  // Reset costs to zero.
+  m->reset(0);
+
+  // Assume the matrix is zero till proven otherwise. Zero matrices will be
+  // optimized away as in the interference case.
+  bool isZeroMatrix = true;
+
+  // Row index. Starts at 1, since the 0th row is for the spill option, which
+  // is always zero.
+  unsigned ri = 1;
+
+  // Iterate over the allowed sets, insert coalescing benefits where
+  // appropriate.
+  for (RegContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end();
+       a1Itr != a1End; ++a1Itr) {
+
+    // Column index, starts at 1 as for row index.
+    unsigned ci = 1;
+    unsigned reg1 = *a1Itr;
+
+    for (RegContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end();
+         a2Itr != a2End; ++a2Itr) {
+
+      // If the row and column represent the same register insert a beneficial
+      // cost to preference this allocation - it would allow us to eliminate a
+      // move instruction.      
+      if (reg1 == *a2Itr) {
+        (*m)[ri][ci] = -cBenefit;
+        isZeroMatrix = false;
+      }
+
+      ++ci;
+    }
+
+    ++ri;
+  }
+
+  // If this turns out to be a zero matrix...
+  if (isZeroMatrix) {
+    // ...free it and return null.
+    delete m;
+    return 0;
+  }
+
+  return m;
+}
+
+PBQPRegAlloc::CoalesceMap PBQPRegAlloc::findCoalesces() {
+
+  typedef MachineFunction::const_iterator MFIterator;
+  typedef MachineBasicBlock::const_iterator MBBIterator;
+  typedef LiveInterval::const_vni_iterator VNIIterator;
+ 
+  CoalesceMap coalescesFound;
+
+  // To find coalesces we need to iterate over the function looking for
+  // copy instructions.
+  for (MFIterator bbItr = mf->begin(), bbEnd = mf->end();
        bbItr != bbEnd; ++bbItr) {
 
     const MachineBasicBlock *mbb = &*bbItr;
-    float loopDepth = loopInfo->getLoopDepth(mbb);
 
-    for (MachineBasicBlock::const_iterator
+    for (MBBIterator iItr = mbb->begin(), iEnd = mbb->end();
-         iItr = mbb->begin(), iEnd = mbb->end(); iItr != iEnd; ++iItr) {
+         iItr != iEnd; ++iItr) {
 
       const MachineInstr *instr = &*iItr;
+      unsigned srcReg, dstReg;
 
-      for (unsigned opNo = 0; opNo < instr->getNumOperands(); ++opNo) {
+      // If this isn't a copy then continue to the next instruction.
+      if (!tii->isMoveInstr(*instr, srcReg, dstReg))
+        continue;
 
-        const MachineOperand &mo = instr->getOperand(opNo);
+      // If the registers are already the same our job is nice and easy.
+      if (dstReg == srcReg)
+        continue;
 
-        // We're not interested in non-registers...
+      bool srcRegIsPhysical = TargetRegisterInfo::isPhysicalRegister(srcReg),
-        if (!mo.isReg())
+           dstRegIsPhysical = TargetRegisterInfo::isPhysicalRegister(dstReg);
+
+      // If both registers are physical then we can't coalesce.
+      if (srcRegIsPhysical && dstRegIsPhysical)
+        continue;
+      
+      // If it's a copy that includes a virtual register but the source and
+      // destination classes differ then we can't coalesce, so continue with
+      // the next instruction.
+      const TargetRegisterClass *srcRegClass = srcRegIsPhysical ?
+          tri->getPhysicalRegisterRegClass(srcReg) : mri->getRegClass(srcReg);
+
+      const TargetRegisterClass *dstRegClass = dstRegIsPhysical ?
+          tri->getPhysicalRegisterRegClass(dstReg) : mri->getRegClass(dstReg);
+
+      if (srcRegClass != dstRegClass)
+        continue;
+
+      // We also need any physical regs to be allocable, coalescing with
+      // a non-allocable register is invalid.
+      if (srcRegIsPhysical) {
+        if (std::find(srcRegClass->allocation_order_begin(*mf),
+                      srcRegClass->allocation_order_end(*mf), srcReg) ==
+            srcRegClass->allocation_order_end(*mf))
           continue;
- 
-        unsigned moReg = mo.getReg();
-
-        // ...Or invalid registers...
-        if (moReg == 0)
-          continue;
-
-        // ...Or physical registers...
-        if (TargetRegisterInfo::isPhysicalRegister(moReg)) 
-          continue;
-
-        assert ((mo.isUse() || mo.isDef()) &&
-                "Not a use, not a def, what is it?");
-
-        //... Just the virtual registers. We treat loads and stores as equal.
-        li->getInterval(moReg).weight += powf(10.0f, loopDepth);
       }
 
+      if (dstRegIsPhysical) {
+        if (std::find(dstRegClass->allocation_order_begin(*mf),
+                      dstRegClass->allocation_order_end(*mf), dstReg) ==
+            dstRegClass->allocation_order_end(*mf))
+          continue;
+      }
+
+      // If we've made it here we have a copy with compatible register classes.
+      // We can probably coalesce, but we need to consider overlap. 
+      const LiveInterval *srcLI = &lis->getInterval(srcReg),
+                         *dstLI = &lis->getInterval(dstReg);
+
+      if (srcLI->overlaps(*dstLI)) {
+        // Even in the case of an overlap we might still be able to coalesce,
+        // but we need to make sure that no definition of either range occurs
+        // while the other range is live.
+
+        // Otherwise start by assuming we're ok.
+        bool badDef = false;
+
+        // Test all defs of the source range.
+        for (VNIIterator 
+               vniItr = srcLI->vni_begin(), vniEnd = srcLI->vni_end();
+               vniItr != vniEnd; ++vniItr) {
+
+          // If we find a def that kills the coalescing opportunity then
+          // record it and break from the loop.
+          if (dstLI->liveAt((*vniItr)->def)) {
+            badDef = true;
+            break;
+          }
+        }
+
+        // If we have a bad def give up, continue to the next instruction.
+        if (badDef)
+          continue;
+         
+        // Otherwise test definitions of the destination range.
+        for (VNIIterator
+               vniItr = dstLI->vni_begin(), vniEnd = dstLI->vni_end();
+               vniItr != vniEnd; ++vniItr) {
+         
+          // We want to make sure we skip the copy instruction itself.
+          if ((*vniItr)->copy == instr)
+            continue;
+
+          if (srcLI->liveAt((*vniItr)->def)) {
+            badDef = true;
+            break;
+          }
+        }
+        
+        // As before a bad def we give up and continue to the next instr.
+        if (badDef)
+          continue;
+      }
+
+      // If we make it to here then either the ranges didn't overlap, or they
+      // did, but none of their definitions would prevent us from coalescing.
+      // We're good to go with the coalesce.
+
+      float cBenefit = powf(10.0f, loopInfo->getLoopDepth(mbb)) / 5.0;
+      
+      coalescesFound[RegPair(srcReg, dstReg)] = cBenefit;
+      coalescesFound[RegPair(dstReg, srcReg)] = cBenefit;
     }
 
   }
 
+  return coalescesFound;
+}
+
+void PBQPRegAlloc::findVRegIntervalsToAlloc() {
+
+  // Iterate over all live ranges.
+  for (LiveIntervals::iterator itr = lis->begin(), end = lis->end();
+       itr != end; ++itr) {
+
+    // Ignore physical ones.
+    if (TargetRegisterInfo::isPhysicalRegister(itr->first))
+      continue;
+
+    LiveInterval *li = itr->second;
+
+    // If this live interval is non-empty we will use pbqp to allocate it.
+    // Empty intervals we allocate in a simple post-processing stage in
+    // finalizeAlloc.
+    if (!li->empty()) {
+      vregIntervalsToAlloc.insert(li);
+    }
+    else {
+      emptyVRegIntervals.insert(li);
+    }
+  }
 }
 
 pbqp* PBQPRegAlloc::constructPBQPProblem() {
 
   typedef std::vector<const LiveInterval*> LIVector;
-  typedef std::set<unsigned> RegSet;
+  typedef std::vector<unsigned> RegVector;
 
-  // These will store the physical & virtual intervals, respectively.
+  // This will store the physical intervals for easy reference.
-  LIVector physIntervals, virtIntervals;
+  LIVector physIntervals;
 
   // Start by clearing the old node <-> live interval mappings & allowed sets
   li2Node.clear();
   node2LI.clear();
   allowedSets.clear();
 
-  // Iterate over intervals classifying them as physical or virtual, and
+  // Populate physIntervals, update preg use:
-  // constructing live interval <-> node number mappings.
+  for (LiveIntervals::iterator itr = lis->begin(), end = lis->end();
-  for (LiveIntervals::iterator itr = li->begin(), end = li->end();
        itr != end; ++itr) {
 
-    if (itr->second->getNumValNums() != 0) {
-      DOUT << "Live range has " << itr->second->getNumValNums() << ": " << itr->second << "\n";
-    }
-
     if (TargetRegisterInfo::isPhysicalRegister(itr->first)) {
       physIntervals.push_back(itr->second);
       mri->setPhysRegUsed(itr->second->reg);
     }
-    else {
-
-      // If we've allocated this virtual register interval a stack slot on a
-      // previous round then it's not an allocation candidate
-      if (ignoreSet.find(itr->first) != ignoreSet.end())
-        continue;
-
-      li2Node[itr->second] = node2LI.size();
-      node2LI.push_back(itr->second);
-      virtIntervals.push_back(itr->second);
-    }
   }
 
-  // Early out if there's no regs to allocate for.
+  // Iterate over vreg intervals, construct live interval <-> node number
-  if (virtIntervals.empty())
+  //  mappings.
-    return 0;
+  for (LiveIntervalSet::const_iterator 
+       itr = vregIntervalsToAlloc.begin(), end = vregIntervalsToAlloc.end();
+       itr != end; ++itr) {
+    const LiveInterval *li = *itr;
+
+    li2Node[li] = node2LI.size();
+    node2LI.push_back(li);
+  }
+
+  // Get the set of potential coalesces.
+  CoalesceMap coalesces(findCoalesces());
 
   // Construct a PBQP solver for this problem
-  pbqp *solver = alloc_pbqp(virtIntervals.size());
+  pbqp *solver = alloc_pbqp(vregIntervalsToAlloc.size());
 
   // Resize allowedSets container appropriately.
-  allowedSets.resize(virtIntervals.size());
+  allowedSets.resize(vregIntervalsToAlloc.size());
 
   // Iterate over virtual register intervals to compute allowed sets...
   for (unsigned node = 0; node < node2LI.size(); ++node) {
@@ -348,36 +547,46 @@ pbqp* PBQPRegAlloc::constructPBQPProblem() {
     const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
     
     // Start by assuming all allocable registers in the class are allowed...
-    RegSet liAllowed(liRC->allocation_order_begin(*mf),
+    RegVector liAllowed(liRC->allocation_order_begin(*mf),
-                     liRC->allocation_order_end(*mf));
+                        liRC->allocation_order_end(*mf));
 
-    // If this range is non-empty then eliminate the physical registers which
+    // Eliminate the physical registers which overlap with this range, along
-    // overlap with this range, along with all their aliases.
+    // with all their aliases.
-    if (!li->empty()) {
+    for (LIVector::iterator pItr = physIntervals.begin(),
-      for (LIVector::iterator pItr = physIntervals.begin(),
+       pEnd = physIntervals.end(); pItr != pEnd; ++pItr) {
-           pEnd = physIntervals.end(); pItr != pEnd; ++pItr) {
 
-        if (li->overlaps(**pItr)) {
+      if (!li->overlaps(**pItr))
+        continue;
 
-          unsigned pReg = (*pItr)->reg;
+      unsigned pReg = (*pItr)->reg;
 
-          // Remove the overlapping reg...
+      // If we get here then the live intervals overlap, but we're still ok
-          liAllowed.erase(pReg);
+      // if they're coalescable.
+      if (coalesces.find(RegPair(li->reg, pReg)) != coalesces.end())
+        continue;
 
-          const unsigned *aliasItr = tri->getAliasSet(pReg);
+      // If we get here then we have a genuine exclusion.
 
-          if (aliasItr != 0) {
+      // Remove the overlapping reg...
-            // ...and its aliases.
+      RegVector::iterator eraseItr =
-            for (; *aliasItr != 0; ++aliasItr) {
+        std::find(liAllowed.begin(), liAllowed.end(), pReg);
-              liAllowed.erase(*aliasItr);
+      
-            }
+      if (eraseItr != liAllowed.end())
+        liAllowed.erase(eraseItr);
 
+      const unsigned *aliasItr = tri->getAliasSet(pReg);
+
+      if (aliasItr != 0) {
+        // ...and its aliases.
+        for (; *aliasItr != 0; ++aliasItr) {
+          RegVector::iterator eraseItr =
+            std::find(liAllowed.begin(), liAllowed.end(), *aliasItr);
+            
+          if (eraseItr != liAllowed.end()) {
+            liAllowed.erase(eraseItr);
           }
-        
         }
-
       }
-
     }
 
     // Copy the allowed set into a member vector for use when constructing cost
@@ -391,33 +600,36 @@ pbqp* PBQPRegAlloc::constructPBQPProblem() {
 
     // Build a cost vector for this interval.
     add_pbqp_nodecosts(solver, node,
-                       buildCostVector(allowedSets[node], spillCost));
+                       buildCostVector(li->reg, allowedSets[node], coalesces,
+                                       spillCost));
 
   }
 
+
   // Now add the cost matrices...
   for (unsigned node1 = 0; node1 < node2LI.size(); ++node1) {
-      
     const LiveInterval *li = node2LI[node1];
 
-    if (li->empty())
-      continue;
- 
     // Test for live range overlaps and insert interference matrices.
     for (unsigned node2 = node1 + 1; node2 < node2LI.size(); ++node2) {
       const LiveInterval *li2 = node2LI[node2];
 
-      if (li2->empty())
+      CoalesceMap::const_iterator cmItr =
-        continue;
+        coalesces.find(RegPair(li->reg, li2->reg));
 
-      if (li->overlaps(*li2)) {
+      PBQPMatrix *m = 0;
-        PBQPMatrix *m =
-          buildInterferenceMatrix(allowedSets[node1], allowedSets[node2]);
 
-        if (m != 0) {
+      if (cmItr != coalesces.end()) {
-          add_pbqp_edgecosts(solver, node1, node2, m);
+        m = buildCoalescingMatrix(allowedSets[node1], allowedSets[node2],
-          delete m;
+                                  cmItr->second);
-        }
+      }
+      else if (li->overlaps(*li2)) {
+        m = buildInterferenceMatrix(allowedSets[node1], allowedSets[node2]);
+      }
+ 
+      if (m != 0) {
+        add_pbqp_edgecosts(solver, node1, node2, m);
+        delete m;
       }
     }
   }
@@ -426,6 +638,25 @@ pbqp* PBQPRegAlloc::constructPBQPProblem() {
   return solver; 
 }
 
+void PBQPRegAlloc::addStackInterval(const LiveInterval *spilled, float &weight) {
+  int stackSlot = vrm->getStackSlot(spilled->reg);
+  
+  if (stackSlot == VirtRegMap::NO_STACK_SLOT) 
+    return;
+
+  LiveInterval &stackInterval = lss->getOrCreateInterval(stackSlot);
+  stackInterval.weight += weight;
+
+  VNInfo *vni;
+  if (stackInterval.getNumValNums() != 0)
+    vni = stackInterval.getValNumInfo(0);
+  else
+    vni = stackInterval.getNextValue(-0U, 0, lss->getVNInfoAllocator());
+
+  LiveInterval &rhsInterval = lis->getInterval(spilled->reg);
+  stackInterval.MergeRangesInAsValue(rhsInterval, vni);
+}
+
 bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) {
   
   // Set to true if we have any spills
@@ -436,7 +667,7 @@ bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) {
   
   // Iterate over the nodes mapping the PBQP solution to a register assignment.
   for (unsigned node = 0; node < node2LI.size(); ++node) {
-    unsigned symReg = node2LI[node]->reg,
+    unsigned virtReg = node2LI[node]->reg,
              allocSelection = get_pbqp_solution(problem, node);
 
     // If the PBQP solution is non-zero it's a physical register...
@@ -444,24 +675,48 @@ bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) {
       // Get the physical reg, subtracting 1 to account for the spill option.
       unsigned physReg = allowedSets[node][allocSelection - 1];
 
+      DOUT << "VREG " << virtReg << " -> " << tri->getName(physReg) << "\n";
+
+      assert(physReg != 0);
+
       // Add to the virt reg map and update the used phys regs.
-      vrm->assignVirt2Phys(symReg, physReg);
+      vrm->assignVirt2Phys(virtReg, physReg);
-      mri->setPhysRegUsed(physReg);
     }
     // ...Otherwise it's a spill.
     else {
 
       // Make sure we ignore this virtual reg on the next round
       // of allocation
-      ignoreSet.insert(node2LI[node]->reg);
+      vregIntervalsToAlloc.erase(&lis->getInterval(virtReg));
 
-      float SSWeight;
+      float ssWeight;
 
       // Insert spill ranges for this live range
+      const LiveInterval *spillInterval = node2LI[node];
+      double oldSpillWeight = spillInterval->weight;
       SmallVector<LiveInterval*, 8> spillIs;
       std::vector<LiveInterval*> newSpills =
-        li->addIntervalsForSpills(*node2LI[node], spillIs, loopInfo, *vrm,
+        lis->addIntervalsForSpills(*spillInterval, spillIs, loopInfo, *vrm,
-                                  SSWeight);
+                                   ssWeight);
+      addStackInterval(spillInterval, ssWeight);
+
+      DOUT << "VREG " << virtReg << " -> SPILLED (Cost: "
+           << oldSpillWeight << ", New vregs: ";
+
+      // Copy any newly inserted live intervals into the list of regs to
+      // allocate.
+      for (std::vector<LiveInterval*>::const_iterator
+           itr = newSpills.begin(), end = newSpills.end();
+           itr != end; ++itr) {
+
+        assert(!(*itr)->empty() && "Empty spill range.");
+
+        DOUT << (*itr)->reg << " ";
+
+        vregIntervalsToAlloc.insert(*itr);
+      }
+
+      DOUT << ")\n";
 
       // We need another round if spill intervals were added.
       anotherRoundNeeded |= !newSpills.empty();
@@ -471,19 +726,86 @@ bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) {
   return !anotherRoundNeeded;
 }
 
+void PBQPRegAlloc::finalizeAlloc() const {
+  typedef LiveIntervals::iterator LIIterator;
+  typedef LiveInterval::Ranges::const_iterator LRIterator;
+
+  // First allocate registers for the empty intervals.
+  for (LiveIntervalSet::iterator
+	 itr = emptyVRegIntervals.begin(), end = emptyVRegIntervals.end();
+         itr != end; ++itr) {
+    LiveInterval *li = *itr;   
+
+    unsigned physReg = li->preference;
+
+    if (physReg == 0) {
+      const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
+      physReg = *liRC->allocation_order_begin(*mf); 
+    }
+       
+    vrm->assignVirt2Phys(li->reg, physReg); 
+  }
+ 
+  // Finally iterate over the basic blocks to compute and set the live-in sets.
+  SmallVector<MachineBasicBlock*, 8> liveInMBBs;
+  MachineBasicBlock *entryMBB = &*mf->begin();
+
+  for (LIIterator liItr = lis->begin(), liEnd = lis->end();
+       liItr != liEnd; ++liItr) {
+
+    const LiveInterval *li = liItr->second;
+    unsigned reg = 0;
+    
+    // Get the physical register for this interval
+    if (TargetRegisterInfo::isPhysicalRegister(li->reg)) {
+      reg = li->reg;
+    }
+    else if (vrm->isAssignedReg(li->reg)) {
+      reg = vrm->getPhys(li->reg);
+    }
+    else {
+      // Ranges which are assigned a stack slot only are ignored.
+      continue;
+    }
+
+    // Iterate over the ranges of the current interval...
+    for (LRIterator lrItr = li->begin(), lrEnd = li->end();
+         lrItr != lrEnd; ++lrItr) {
+      
+      // Find the set of basic blocks which this range is live into...
+      if (lis->findLiveInMBBs(lrItr->start, lrItr->end,  liveInMBBs)) {
+        // And add the physreg for this interval to their live-in sets.
+        for (unsigned i = 0; i < liveInMBBs.size(); ++i) {
+          if (liveInMBBs[i] != entryMBB) {
+            if (!liveInMBBs[i]->isLiveIn(reg)) {
+              liveInMBBs[i]->addLiveIn(reg);
+            }
+          }
+        }
+        liveInMBBs.clear();
+      }
+    }
+  }
+ 
+}
+
 bool PBQPRegAlloc::runOnMachineFunction(MachineFunction &MF) {
-  
+
   mf = &MF;
   tm = &mf->getTarget();
   tri = tm->getRegisterInfo();
+  tii = tm->getInstrInfo();
   mri = &mf->getRegInfo();
 
-  li = &getAnalysis<LiveIntervals>();
+  lis = &getAnalysis<LiveIntervals>();
+  lss = &getAnalysis<LiveStacks>();
   loopInfo = &getAnalysis<MachineLoopInfo>();
 
   std::auto_ptr<VirtRegMap> vrmAutoPtr(new VirtRegMap(*mf));
   vrm = vrmAutoPtr.get();
 
+  DOUT << "PBQP Register Allocating for " << mf->getFunction()->getName() << "\n";
+
   // Allocator main loop:
   // 
   // * Map current regalloc problem to a PBQP problem
@@ -493,31 +815,49 @@ bool PBQPRegAlloc::runOnMachineFunction(MachineFunction &MF) {
   // 
   // This process is continued till no more spills are generated.
 
-  bool regallocComplete = false;
+  // Find the vreg intervals in need of allocation.
+  findVRegIntervalsToAlloc();
   
-  // Calculate spill costs for intervals
+  // If there aren't any then we're done here.
-  calcSpillCosts();
+  if (vregIntervalsToAlloc.empty() && emptyVRegIntervals.empty())
+    return true;
 
-  while (!regallocComplete) {
+  // If there are non-empty intervals allocate them using pbqp.
-    pbqp *problem = constructPBQPProblem();
+  if (!vregIntervalsToAlloc.empty()) {
-   
-    // Fast out if there's no problem to solve.
-    if (problem == 0)
-      return true;
- 
-    solve_pbqp(problem);
-   
-    regallocComplete = mapPBQPToRegAlloc(problem);
 
-    free_pbqp(problem); 
+    bool pbqpAllocComplete = false;
+    unsigned round = 0;
+
+    while (!pbqpAllocComplete) {
+      DOUT << "  PBQP Regalloc round " << round << ":\n";
+
+      pbqp *problem = constructPBQPProblem();
+   
+      solve_pbqp(problem);
+   
+      pbqpAllocComplete = mapPBQPToRegAlloc(problem);
+
+      free_pbqp(problem); 
+
+      ++round;
+    }
   }
 
-  ignoreSet.clear();
+  // Finalise allocation, allocate empty ranges.
+  finalizeAlloc();
 
+  vregIntervalsToAlloc.clear();
+  emptyVRegIntervals.clear();
+  li2Node.clear();
+  node2LI.clear();
+  allowedSets.clear();
+
+  DOUT << "Post alloc VirtRegMap:\n" << *vrm << "\n";
+
+  // Run spiller
   std::auto_ptr<Spiller> spiller(createSpiller());
-
   spiller->runOnMachineFunction(*mf, *vrm);
-    
+
   return true; 
 }
 
@@ -527,4 +867,3 @@ FunctionPass* llvm::createPBQPRegisterAllocator() {
 
 
 #undef DEBUG_TYPE
-