lib/CodeGen/StrongPHIElimination.cpp

   1 //===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This pass eliminates machine instruction PHI nodes by inserting copy
  11 // instructions, using an intelligent copy-folding technique based on
  12 // dominator information.  This is technique is derived from:
  13 //
  14 //    Budimlic, et al. Fast copy coalescing and live-range identification.
  15 //    In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language
  16 //    Design and Implementation (Berlin, Germany, June 17 - 19, 2002).
  17 //    PLDI '02. ACM, New York, NY, 25-32.
  18 //    DOI= http://doi.acm.org/10.1145/512529.512534
  19 //
  20 //===----------------------------------------------------------------------===//
  21
  22 #define DEBUG_TYPE "strongphielim"
  23 #include "llvm/CodeGen/Passes.h"
  24 #include "llvm/CodeGen/LiveVariables.h"
  25 #include "llvm/CodeGen/MachineDominators.h"
  26 #include "llvm/CodeGen/MachineFunctionPass.h"
  27 #include "llvm/CodeGen/MachineInstr.h"
  28 #include "llvm/CodeGen/MachineRegisterInfo.h"
  29 #include "llvm/Target/TargetInstrInfo.h"
  30 #include "llvm/Target/TargetMachine.h"
  31 #include "llvm/ADT/DepthFirstIterator.h"
  32 #include "llvm/ADT/Statistic.h"
  33 #include "llvm/Support/Compiler.h"
  34 using namespace llvm;
  35
  36
  37 namespace {
  38   struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass {
  39     static char ID; // Pass identification, replacement for typeid
  40     StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {}
  41
  42     DenseMap<MachineBasicBlock*,
  43              std::map<unsigned, unsigned> > Waiting;
  44
  45     std::map<unsigned, std::vector<unsigned> > Stacks;
  46     std::set<unsigned> UsedByAnother;
  47     std::map<unsigned, std::set<unsigned> > RenameSets;
  48
  49     bool runOnMachineFunction(MachineFunction &Fn);
  50
  51     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  52       AU.addRequired<MachineDominatorTree>();
  53       AU.addRequired<LiveVariables>();
  54       MachineFunctionPass::getAnalysisUsage(AU);
  55     }
  56
  57     virtual void releaseMemory() {
  58       preorder.clear();
  59       maxpreorder.clear();
  60
  61       Waiting.clear();
  62     }
  63
  64   private:
  65     struct DomForestNode {
  66     private:
  67       std::vector<DomForestNode*> children;
  68       unsigned reg;
  69
  70       void addChild(DomForestNode* DFN) { children.push_back(DFN); }
  71
  72     public:
  73       typedef std::vector<DomForestNode*>::iterator iterator;
  74
  75       DomForestNode(unsigned r, DomForestNode* parent) : reg(r) {
  76         if (parent)
  77           parent->addChild(this);
  78       }
  79
  80       ~DomForestNode() {
  81         for (iterator I = begin(), E = end(); I != E; ++I)
  82           delete *I;
  83       }
  84
  85       inline unsigned getReg() { return reg; }
  86
  87       inline DomForestNode::iterator begin() { return children.begin(); }
  88       inline DomForestNode::iterator end() { return children.end(); }
  89     };
  90
  91     DenseMap<MachineBasicBlock*, unsigned> preorder;
  92     DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
  93
  94
  95     void computeDFS(MachineFunction& MF);
  96     void processBlock(MachineBasicBlock* MBB);
  97
  98     std::vector<DomForestNode*> computeDomForest(std::set<unsigned>& instrs);
  99     void processPHIUnion(MachineInstr* Inst,
 100                          std::set<unsigned>& PHIUnion,
 101                          std::vector<StrongPHIElimination::DomForestNode*>& DF,
 102                          std::vector<std::pair<unsigned, unsigned> >& locals);
 103     void ScheduleCopies(MachineBasicBlock* MBB, std::set<unsigned>& pushed);
 104     void InsertCopies(MachineBasicBlock* MBB, std::set<MachineBasicBlock*>& v);
 105   };
 106
 107   char StrongPHIElimination::ID = 0;
 108   RegisterPass<StrongPHIElimination> X("strong-phi-node-elimination",
 109                   "Eliminate PHI nodes for register allocation, intelligently");
 110 }
 111
 112 const PassInfo *llvm::StrongPHIEliminationID = X.getPassInfo();
 113
 114 /// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree
 115 /// of the given MachineFunction.  These numbers are then used in other parts
 116 /// of the PHI elimination process.
 117 void StrongPHIElimination::computeDFS(MachineFunction& MF) {
 118   SmallPtrSet<MachineDomTreeNode*, 8> frontier;
 119   SmallPtrSet<MachineDomTreeNode*, 8> visited;
 120
 121   unsigned time = 0;
 122
 123   MachineDominatorTree& DT = getAnalysis<MachineDominatorTree>();
 124
 125   MachineDomTreeNode* node = DT.getRootNode();
 126
 127   std::vector<MachineDomTreeNode*> worklist;
 128   worklist.push_back(node);
 129
 130   while (!worklist.empty()) {
 131     MachineDomTreeNode* currNode = worklist.back();
 132
 133     if (!frontier.count(currNode)) {
 134       frontier.insert(currNode);
 135       ++time;
 136       preorder.insert(std::make_pair(currNode->getBlock(), time));
 137     }
 138
 139     bool inserted = false;
 140     for (MachineDomTreeNode::iterator I = node->begin(), E = node->end();
 141          I != E; ++I)
 142       if (!frontier.count(*I) && !visited.count(*I)) {
 143         worklist.push_back(*I);
 144         inserted = true;
 145         break;
 146       }
 147
 148     if (!inserted) {
 149       frontier.erase(currNode);
 150       visited.insert(currNode);
 151       maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
 152
 153       worklist.pop_back();
 154     }
 155   }
 156 }
 157
 158 /// PreorderSorter - a helper class that is used to sort registers
 159 /// according to the preorder number of their defining blocks
 160 class PreorderSorter {
 161 private:
 162   DenseMap<MachineBasicBlock*, unsigned>& preorder;
 163   LiveVariables& LV;
 164
 165 public:
 166   PreorderSorter(DenseMap<MachineBasicBlock*, unsigned>& p,
 167                 LiveVariables& L) : preorder(p), LV(L) { }
 168
 169   bool operator()(unsigned A, unsigned B) {
 170     if (A == B)
 171       return false;
 172
 173     MachineBasicBlock* ABlock = LV.getVarInfo(A).DefInst->getParent();
 174     MachineBasicBlock* BBlock = LV.getVarInfo(A).DefInst->getParent();
 175
 176     if (preorder[ABlock] < preorder[BBlock])
 177       return true;
 178     else if (preorder[ABlock] > preorder[BBlock])
 179       return false;
 180
 181     return false;
 182   }
 183 };
 184
 185 /// computeDomForest - compute the subforest of the DomTree corresponding
 186 /// to the defining blocks of the registers in question
 187 std::vector<StrongPHIElimination::DomForestNode*>
 188 StrongPHIElimination::computeDomForest(std::set<unsigned>& regs) {
 189   LiveVariables& LV = getAnalysis<LiveVariables>();
 190
 191   DomForestNode* VirtualRoot = new DomForestNode(0, 0);
 192   maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL));
 193
 194   std::vector<unsigned> worklist;
 195   worklist.reserve(regs.size());
 196   for (std::set<unsigned>::iterator I = regs.begin(), E = regs.end();
 197        I != E; ++I)
 198     worklist.push_back(*I);
 199
 200   PreorderSorter PS(preorder, LV);
 201   std::sort(worklist.begin(), worklist.end(), PS);
 202
 203   DomForestNode* CurrentParent = VirtualRoot;
 204   std::vector<DomForestNode*> stack;
 205   stack.push_back(VirtualRoot);
 206
 207   for (std::vector<unsigned>::iterator I = worklist.begin(), E = worklist.end();
 208        I != E; ++I) {
 209     unsigned pre = preorder[LV.getVarInfo(*I).DefInst->getParent()];
 210     MachineBasicBlock* parentBlock = CurrentParent->getReg() ?
 211                  LV.getVarInfo(CurrentParent->getReg()).DefInst->getParent() :
 212                  0;
 213
 214     while (pre > maxpreorder[parentBlock]) {
 215       stack.pop_back();
 216       CurrentParent = stack.back();
 217
 218       parentBlock = LV.getVarInfo(CurrentParent->getReg()).DefInst->getParent();
 219     }
 220
 221     DomForestNode* child = new DomForestNode(*I, CurrentParent);
 222     stack.push_back(child);
 223     CurrentParent = child;
 224   }
 225
 226   std::vector<DomForestNode*> ret;
 227   ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end());
 228   return ret;
 229 }
 230
 231 /// isLiveIn - helper method that determines, from a VarInfo, if a register
 232 /// is live into a block
 233 static bool isLiveIn(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
 234   if (V.AliveBlocks.test(MBB->getNumber()))
 235     return true;
 236
 237   if (V.DefInst->getParent() != MBB &&
 238       V.UsedBlocks.test(MBB->getNumber()))
 239     return true;
 240
 241   return false;
 242 }
 243
 244 /// isLiveOut - help method that determines, from a VarInfo, if a register is
 245 /// live out of a block.
 246 static bool isLiveOut(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
 247   if (MBB == V.DefInst->getParent() ||
 248       V.UsedBlocks.test(MBB->getNumber())) {
 249     for (std::vector<MachineInstr*>::iterator I = V.Kills.begin(),
 250          E = V.Kills.end(); I != E; ++I)
 251       if ((*I)->getParent() == MBB)
 252         return false;
 253
 254     return true;
 255   }
 256
 257   return false;
 258 }
 259
 260 /// isKillInst - helper method that determines, from a VarInfo, if an
 261 /// instruction kills a given register
 262 static bool isKillInst(LiveVariables::VarInfo& V, MachineInstr* MI) {
 263   return std::find(V.Kills.begin(), V.Kills.end(), MI) != V.Kills.end();
 264 }
 265
 266 /// interferes - checks for local interferences by scanning a block.  The only
 267 /// trick parameter is 'mode' which tells it the relationship of the two
 268 /// registers. 0 - defined in the same block, 1 - first properly dominates
 269 /// second, 2 - second properly dominates first
 270 static bool interferes(LiveVariables::VarInfo& First, LiveVariables::VarInfo& Second,
 271                 MachineBasicBlock* scan, unsigned mode) {
 272   MachineInstr* def = 0;
 273   MachineInstr* kill = 0;
 274
 275   bool interference = false;
 276
 277   // Wallk the block, checking for interferences
 278   for (MachineBasicBlock::iterator MBI = scan->begin(), MBE = scan->end();
 279        MBI != MBE; ++MBI) {
 280     MachineInstr* curr = MBI;
 281
 282     // Same defining block...
 283     if (mode == 0) {
 284       if (curr == First.DefInst) {
 285         // If we find our first DefInst, save it
 286         if (!def) {
 287           def = curr;
 288         // If there's already an unkilled DefInst, then
 289         // this is an interference
 290         } else if (!kill) {
 291           interference = true;
 292           break;
 293         // If there's a DefInst followed by a KillInst, then
 294         // they can't interfere
 295         } else {
 296           interference = false;
 297           break;
 298         }
 299       // Symmetric with the above
 300       } else if (curr == Second.DefInst ) {
 301         if (!def) {
 302           def = curr;
 303         } else if (!kill) {
 304           interference = true;
 305           break;
 306         } else {
 307           interference = false;
 308           break;
 309         }
 310       // Store KillInsts if they match up with the DefInst
 311       } else if (isKillInst(First, curr)) {
 312         if (def == First.DefInst) {
 313           kill = curr;
 314         } else if (isKillInst(Second, curr)) {
 315           if (def == Second.DefInst) {
 316             kill = curr;
 317           }
 318         }
 319       }
 320     // First properly dominates second...
 321     } else if (mode == 1) {
 322       if (curr == Second.DefInst) {
 323         // DefInst of second without kill of first is an interference
 324         if (!kill) {
 325           interference = true;
 326           break;
 327         // DefInst after a kill is a non-interference
 328         } else {
 329           interference = false;
 330           break;
 331         }
 332       // Save KillInsts of First
 333       } else if (isKillInst(First, curr)) {
 334         kill = curr;
 335       }
 336     // Symmetric with the above
 337     } else if (mode == 2) {
 338       if (curr == First.DefInst) {
 339         if (!kill) {
 340           interference = true;
 341           break;
 342         } else {
 343           interference = false;
 344           break;
 345         }
 346       } else if (isKillInst(Second, curr)) {
 347         kill = curr;
 348       }
 349     }
 350   }
 351
 352   return interference;
 353 }
 354
 355 /// processBlock - Eliminate PHIs in the given block
 356 void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
 357   LiveVariables& LV = getAnalysis<LiveVariables>();
 358
 359   // Holds names that have been added to a set in any PHI within this block
 360   // before the current one.
 361   std::set<unsigned> ProcessedNames;
 362
 363   MachineBasicBlock::iterator P = MBB->begin();
 364   while (P->getOpcode() == TargetInstrInfo::PHI) {
 365     LiveVariables::VarInfo& PHIInfo = LV.getVarInfo(P->getOperand(0).getReg());
 366
 367     unsigned DestReg = P->getOperand(0).getReg();
 368
 369     // Hold the names that are currently in the candidate set.
 370     std::set<unsigned> PHIUnion;
 371     std::set<MachineBasicBlock*> UnionedBlocks;
 372
 373     for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
 374       unsigned SrcReg = P->getOperand(i-1).getReg();
 375       LiveVariables::VarInfo& SrcInfo = LV.getVarInfo(SrcReg);
 376
 377       // Check for trivial interferences
 378       if (isLiveIn(SrcInfo, P->getParent()) ||
 379           isLiveOut(PHIInfo, SrcInfo.DefInst->getParent()) ||
 380           ( PHIInfo.DefInst->getOpcode() == TargetInstrInfo::PHI &&
 381             isLiveIn(PHIInfo, SrcInfo.DefInst->getParent()) ) ||
 382           ProcessedNames.count(SrcReg) ||
 383           UnionedBlocks.count(SrcInfo.DefInst->getParent())) {
 384
 385         // add a copy from a_i to p in Waiting[From[a_i]]
 386         MachineBasicBlock* From = P->getOperand(i).getMBB();
 387         Waiting[From].insert(std::make_pair(SrcReg, DestReg));
 388         UsedByAnother.insert(SrcReg);
 389       } else {
 390         PHIUnion.insert(SrcReg);
 391         UnionedBlocks.insert(SrcInfo.DefInst->getParent());
 392       }
 393     }
 394
 395     std::vector<StrongPHIElimination::DomForestNode*> DF =
 396                                                      computeDomForest(PHIUnion);
 397
 398     // Walk DomForest to resolve interferences
 399     std::vector<std::pair<unsigned, unsigned> > localInterferences;
 400     processPHIUnion(P, PHIUnion, DF, localInterferences);
 401
 402     // Check for local interferences
 403     for (std::vector<std::pair<unsigned, unsigned> >::iterator I =
 404         localInterferences.begin(), E = localInterferences.end(); I != E; ++I) {
 405       std::pair<unsigned, unsigned> p = *I;
 406
 407       LiveVariables::VarInfo& FirstInfo = LV.getVarInfo(p.first);
 408       LiveVariables::VarInfo& SecondInfo = LV.getVarInfo(p.second);
 409
 410       MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
 411
 412       // Determine the block we need to scan and the relationship between
 413       // the two registers
 414       MachineBasicBlock* scan = 0;
 415       unsigned mode = 0;
 416       if (FirstInfo.DefInst->getParent() == SecondInfo.DefInst->getParent()) {
 417         scan = FirstInfo.DefInst->getParent();
 418         mode = 0; // Same block
 419       } else if (MDT.dominates(FirstInfo.DefInst->getParent(),
 420                              SecondInfo.DefInst->getParent())) {
 421         scan = SecondInfo.DefInst->getParent();
 422         mode = 1; // First dominates second
 423       } else {
 424         scan = FirstInfo.DefInst->getParent();
 425         mode = 2; // Second dominates first
 426       }
 427
 428       // If there's an interference, we need to insert  copies
 429       if (interferes(FirstInfo, SecondInfo, scan, mode)) {
 430         // Insert copies for First
 431         for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
 432           if (P->getOperand(i-1).getReg() == p.first) {
 433             unsigned SrcReg = p.first;
 434             MachineBasicBlock* From = P->getOperand(i).getMBB();
 435
 436             Waiting[From].insert(std::make_pair(SrcReg,
 437                                                 P->getOperand(0).getReg()));
 438             UsedByAnother.insert(SrcReg);
 439
 440             PHIUnion.erase(SrcReg);
 441           }
 442         }
 443       }
 444     }
 445
 446     // Cache renaming information
 447     RenameSets.insert(std::make_pair(P->getOperand(0).getReg(), PHIUnion));
 448
 449     ProcessedNames.insert(PHIUnion.begin(), PHIUnion.end());
 450     ++P;
 451   }
 452 }
 453
 454 /// processPHIUnion - Take a set of candidate registers to be coallesced when
 455 /// decomposing the PHI instruction.  Use the DominanceForest to remove the ones
 456 /// that are known to interfere, and flag others that need to be checked for
 457 /// local interferences.
 458 void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
 459                                            std::set<unsigned>& PHIUnion,
 460                         std::vector<StrongPHIElimination::DomForestNode*>& DF,
 461                         std::vector<std::pair<unsigned, unsigned> >& locals) {
 462
 463   std::vector<DomForestNode*> worklist(DF.begin(), DF.end());
 464   SmallPtrSet<DomForestNode*, 4> visited;
 465
 466   LiveVariables& LV = getAnalysis<LiveVariables>();
 467   unsigned DestReg = Inst->getOperand(0).getReg();
 468
 469   // DF walk on the DomForest
 470   while (!worklist.empty()) {
 471     DomForestNode* DFNode = worklist.back();
 472
 473     LiveVariables::VarInfo& Info = LV.getVarInfo(DFNode->getReg());
 474     visited.insert(DFNode);
 475
 476     bool inserted = false;
 477     for (DomForestNode::iterator CI = DFNode->begin(), CE = DFNode->end();
 478          CI != CE; ++CI) {
 479       DomForestNode* child = *CI;
 480       LiveVariables::VarInfo& CInfo = LV.getVarInfo(child->getReg());
 481
 482       if (isLiveOut(Info, CInfo.DefInst->getParent())) {
 483         // Insert copies for parent
 484         for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
 485           if (Inst->getOperand(i-1).getReg() == DFNode->getReg()) {
 486             unsigned SrcReg = DFNode->getReg();
 487             MachineBasicBlock* From = Inst->getOperand(i).getMBB();
 488
 489             Waiting[From].insert(std::make_pair(SrcReg, DestReg));
 490             UsedByAnother.insert(SrcReg);
 491
 492             PHIUnion.erase(SrcReg);
 493           }
 494         }
 495       } else if (isLiveIn(Info, CInfo.DefInst->getParent()) ||
 496                  Info.DefInst->getParent() == CInfo.DefInst->getParent()) {
 497         // Add (p, c) to possible local interferences
 498         locals.push_back(std::make_pair(DFNode->getReg(), child->getReg()));
 499       }
 500
 501       if (!visited.count(child)) {
 502         worklist.push_back(child);
 503         inserted = true;
 504       }
 505     }
 506
 507     if (!inserted) worklist.pop_back();
 508   }
 509 }
 510
 511 /// ScheduleCopies - Insert copies into predecessor blocks, scheduling
 512 /// them properly so as to avoid the 'lost copy' and the 'virtual swap'
 513 /// problems.
 514 ///
 515 /// Based on "Practical Improvements to the Construction and Destruction
 516 /// of Static Single Assignment Form" by Briggs, et al.
 517 void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB,
 518                                           std::set<unsigned>& pushed) {
 519   // FIXME: This function needs to update LiveVariables
 520   std::map<unsigned, unsigned>& copy_set= Waiting[MBB];
 521
 522   std::map<unsigned, unsigned> worklist;
 523   std::map<unsigned, unsigned> map;
 524
 525   // Setup worklist of initial copies
 526   for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
 527        E = copy_set.end(); I != E; ) {
 528     map.insert(std::make_pair(I->first, I->first));
 529     map.insert(std::make_pair(I->second, I->second));
 530
 531     if (!UsedByAnother.count(I->first)) {
 532       worklist.insert(*I);
 533
 534       // Avoid iterator invalidation
 535       unsigned first = I->first;
 536       ++I;
 537       copy_set.erase(first);
 538     } else {
 539       ++I;
 540     }
 541   }
 542
 543   LiveVariables& LV = getAnalysis<LiveVariables>();
 544   MachineFunction* MF = MBB->getParent();
 545   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
 546
 547   // Iterate over the worklist, inserting copies
 548   while (!worklist.empty() || !copy_set.empty()) {
 549     while (!worklist.empty()) {
 550       std::pair<unsigned, unsigned> curr = *worklist.begin();
 551       worklist.erase(curr.first);
 552
 553       const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
 554
 555       if (isLiveOut(LV.getVarInfo(curr.second), MBB)) {
 556         // Create a temporary
 557         unsigned t = MF->getRegInfo().createVirtualRegister(RC);
 558
 559         // Insert copy from curr.second to a temporary at
 560         // the Phi defining curr.second
 561         LiveVariables::VarInfo VI = LV.getVarInfo(curr.second);
 562         MachineBasicBlock::iterator PI = VI.DefInst;
 563         TII->copyRegToReg(*VI.DefInst->getParent(), PI, t,
 564                           curr.second, RC, RC);
 565
 566         // Push temporary on Stacks
 567         Stacks[curr.second].push_back(t);
 568
 569         // Insert curr.second in pushed
 570         pushed.insert(curr.second);
 571       }
 572
 573       // Insert copy from map[curr.first] to curr.second
 574       TII->copyRegToReg(*MBB, MBB->end(), curr.second,
 575                         map[curr.first], RC, RC);
 576       map[curr.first] = curr.second;
 577
 578       // If curr.first is a destination in copy_set...
 579       for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
 580            E = copy_set.end(); I != E; )
 581         if (curr.first == I->second) {
 582           std::pair<unsigned, unsigned> temp = *I;
 583
 584           // Avoid iterator invalidation
 585           ++I;
 586           copy_set.erase(temp.first);
 587           worklist.insert(temp);
 588
 589           break;
 590         } else {
 591           ++I;
 592         }
 593     }
 594
 595     if (!copy_set.empty()) {
 596       std::pair<unsigned, unsigned> curr = *copy_set.begin();
 597       copy_set.erase(curr.first);
 598
 599       const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
 600
 601       // Insert a copy from dest to a new temporary t at the end of b
 602       unsigned t = MF->getRegInfo().createVirtualRegister(RC);
 603       TII->copyRegToReg(*MBB, MBB->end(), t,
 604                         curr.second, RC, RC);
 605       map[curr.second] = t;
 606
 607       worklist.insert(curr);
 608     }
 609   }
 610 }
 611
 612 /// InsertCopies - insert copies into MBB and all of its successors
 613 void StrongPHIElimination::InsertCopies(MachineBasicBlock* MBB,
 614                                         std::set<MachineBasicBlock*>& visited) {
 615   visited.insert(MBB);
 616
 617   std::set<unsigned> pushed;
 618
 619   // Rewrite register uses from Stacks
 620   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
 621       I != E; ++I)
 622     for (unsigned i = 0; i < I->getNumOperands(); ++i)
 623       if (I->getOperand(i).isRegister() &&
 624           Stacks[I->getOperand(i).getReg()].size()) {
 625         I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back());
 626       }
 627
 628   // Schedule the copies for this block
 629   ScheduleCopies(MBB, pushed);
 630
 631   // Recur to our successors
 632   for (GraphTraits<MachineBasicBlock*>::ChildIteratorType I =
 633        GraphTraits<MachineBasicBlock*>::child_begin(MBB), E =
 634        GraphTraits<MachineBasicBlock*>::child_end(MBB); I != E; ++I)
 635     if (!visited.count(*I))
 636       InsertCopies(*I, visited);
 637
 638   // As we exit this block, pop the names we pushed while processing it
 639   for (std::set<unsigned>::iterator I = pushed.begin(),
 640        E = pushed.end(); I != E; ++I)
 641     Stacks[*I].pop_back();
 642 }
 643
 644 bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
 645   // Compute DFS numbers of each block
 646   computeDFS(Fn);
 647
 648   // Determine which phi node operands need copies
 649   for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
 650     if (!I->empty() &&
 651         I->begin()->getOpcode() == TargetInstrInfo::PHI)
 652       processBlock(I);
 653
 654   // Insert copies
 655   // FIXME: This process should probably preserve LiveVariables
 656   std::set<MachineBasicBlock*> visited;
 657   InsertCopies(Fn.begin(), visited);
 658
 659   // Perform renaming
 660   typedef std::map<unsigned, std::set<unsigned> > RenameSetType;
 661   for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
 662        I != E; ++I)
 663     for (std::set<unsigned>::iterator SI = I->second.begin(),
 664          SE = I->second.end(); SI != SE; ++SI)
 665       Fn.getRegInfo().replaceRegWith(*SI, I->first);
 666
 667   // FIXME: Insert last-minute copies
 668
 669   // Remove PHIs
 670   for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
 671     for (MachineBasicBlock::iterator BI = I->begin(), BE = I->end();
 672          BI != BE; ++BI)
 673       if (BI->getOpcode() == TargetInstrInfo::PHI)
 674         BI->eraseFromParent();
 675
 676   return false;
 677 }