lib/CodeGen/MachineBasicBlock.cpp

   1 //===-- llvm/CodeGen/MachineBasicBlock.cpp ----------------------*- C++ -*-===//
   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 // Collect the sequence of machine instructions for a basic block.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/CodeGen/MachineBasicBlock.h"
  15 #include "llvm/BasicBlock.h"
  16 #include "llvm/CodeGen/MachineFunction.h"
  17 #include "llvm/Target/TargetRegisterInfo.h"
  18 #include "llvm/Target/TargetData.h"
  19 #include "llvm/Target/TargetInstrDesc.h"
  20 #include "llvm/Target/TargetMachine.h"
  21 #include "llvm/Support/LeakDetector.h"
  22 #include "llvm/Support/raw_ostream.h"
  23 #include <algorithm>
  24 using namespace llvm;
  25
  26 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
  27   : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false) {
  28   Insts.Parent = this;
  29 }
  30
  31 MachineBasicBlock::~MachineBasicBlock() {
  32   LeakDetector::removeGarbageObject(this);
  33 }
  34
  35 raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
  36   MBB.print(OS);
  37   return OS;
  38 }
  39
  40 /// addNodeToList (MBB) - When an MBB is added to an MF, we need to update the
  41 /// parent pointer of the MBB, the MBB numbering, and any instructions in the
  42 /// MBB to be on the right operand list for registers.
  43 ///
  44 /// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
  45 /// gets the next available unique MBB number. If it is removed from a
  46 /// MachineFunction, it goes back to being #-1.
  47 void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
  48   MachineFunction &MF = *N->getParent();
  49   N->Number = MF.addToMBBNumbering(N);
  50
  51   // Make sure the instructions have their operands in the reginfo lists.
  52   MachineRegisterInfo &RegInfo = MF.getRegInfo();
  53   for (MachineBasicBlock::iterator I = N->begin(), E = N->end(); I != E; ++I)
  54     I->AddRegOperandsToUseLists(RegInfo);
  55
  56   LeakDetector::removeGarbageObject(N);
  57 }
  58
  59 void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
  60   N->getParent()->removeFromMBBNumbering(N->Number);
  61   N->Number = -1;
  62   LeakDetector::addGarbageObject(N);
  63 }
  64
  65
  66 /// addNodeToList (MI) - When we add an instruction to a basic block
  67 /// list, we update its parent pointer and add its operands from reg use/def
  68 /// lists if appropriate.
  69 void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
  70   assert(N->getParent() == 0 && "machine instruction already in a basic block");
  71   N->setParent(Parent);
  72
  73   // Add the instruction's register operands to their corresponding
  74   // use/def lists.
  75   MachineFunction *MF = Parent->getParent();
  76   N->AddRegOperandsToUseLists(MF->getRegInfo());
  77
  78   LeakDetector::removeGarbageObject(N);
  79 }
  80
  81 /// removeNodeFromList (MI) - When we remove an instruction from a basic block
  82 /// list, we update its parent pointer and remove its operands from reg use/def
  83 /// lists if appropriate.
  84 void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
  85   assert(N->getParent() != 0 && "machine instruction not in a basic block");
  86
  87   // Remove from the use/def lists.
  88   N->RemoveRegOperandsFromUseLists();
  89
  90   N->setParent(0);
  91
  92   LeakDetector::addGarbageObject(N);
  93 }
  94
  95 /// transferNodesFromList (MI) - When moving a range of instructions from one
  96 /// MBB list to another, we need to update the parent pointers and the use/def
  97 /// lists.
  98 void ilist_traits<MachineInstr>::
  99 transferNodesFromList(ilist_traits<MachineInstr> &fromList,
 100                       MachineBasicBlock::iterator first,
 101                       MachineBasicBlock::iterator last) {
 102   assert(Parent->getParent() == fromList.Parent->getParent() &&
 103         "MachineInstr parent mismatch!");
 104
 105   // Splice within the same MBB -> no change.
 106   if (Parent == fromList.Parent) return;
 107
 108   // If splicing between two blocks within the same function, just update the
 109   // parent pointers.
 110   for (; first != last; ++first)
 111     first->setParent(Parent);
 112 }
 113
 114 void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
 115   assert(!MI->getParent() && "MI is still in a block!");
 116   Parent->getParent()->DeleteMachineInstr(MI);
 117 }
 118
 119 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
 120   iterator I = end();
 121   while (I != begin() && (--I)->getDesc().isTerminator())
 122     ; /*noop */
 123   if (I != end() && !I->getDesc().isTerminator()) ++I;
 124   return I;
 125 }
 126
 127 /// isOnlyReachableViaFallthough - Return true if this basic block has
 128 /// exactly one predecessor and the control transfer mechanism between
 129 /// the predecessor and this block is a fall-through.
 130 bool MachineBasicBlock::isOnlyReachableByFallthrough() const {
 131   // If this is a landing pad, it isn't a fall through.  If it has no preds,
 132   // then nothing falls through to it.
 133   if (isLandingPad() || pred_empty())
 134     return false;
 135
 136   // If there isn't exactly one predecessor, it can't be a fall through.
 137   const_pred_iterator PI = pred_begin(), PI2 = PI;
 138   ++PI2;
 139   if (PI2 != pred_end())
 140     return false;
 141
 142   // The predecessor has to be immediately before this block.
 143   const MachineBasicBlock *Pred = *PI;
 144
 145   if (!Pred->isLayoutSuccessor(this))
 146     return false;
 147
 148   // If the block is completely empty, then it definitely does fall through.
 149   if (Pred->empty())
 150     return true;
 151
 152   // Otherwise, check the last instruction.
 153   const MachineInstr &LastInst = Pred->back();
 154   return !LastInst.getDesc().isBarrier();
 155 }
 156
 157 void MachineBasicBlock::dump() const {
 158   print(errs());
 159 }
 160
 161 static inline void OutputReg(raw_ostream &os, unsigned RegNo,
 162                              const TargetRegisterInfo *TRI = 0) {
 163   if (!RegNo || TargetRegisterInfo::isPhysicalRegister(RegNo)) {
 164     if (TRI)
 165       os << " %" << TRI->get(RegNo).Name;
 166     else
 167       os << " %mreg(" << RegNo << ")";
 168   } else
 169     os << " %reg" << RegNo;
 170 }
 171
 172 void MachineBasicBlock::print(raw_ostream &OS) const {
 173   const MachineFunction *MF = getParent();
 174   if (!MF) {
 175     OS << "Can't print out MachineBasicBlock because parent MachineFunction"
 176        << " is null\n";
 177     return;
 178   }
 179
 180   const BasicBlock *LBB = getBasicBlock();
 181   OS << '\n';
 182   if (LBB) OS << LBB->getName() << ": ";
 183   OS << (const void*)this
 184      << ", LLVM BB @" << (const void*) LBB << ", ID#" << getNumber();
 185   if (Alignment) OS << ", Alignment " << Alignment;
 186   if (isLandingPad()) OS << ", EH LANDING PAD";
 187   OS << ":\n";
 188
 189   const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
 190   if (!livein_empty()) {
 191     OS << "Live Ins:";
 192     for (const_livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
 193       OutputReg(OS, *I, TRI);
 194     OS << '\n';
 195   }
 196   // Print the preds of this block according to the CFG.
 197   if (!pred_empty()) {
 198     OS << "    Predecessors according to CFG:";
 199     for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
 200       OS << ' ' << *PI << " (#" << (*PI)->getNumber() << ')';
 201     OS << '\n';
 202   }
 203
 204   for (const_iterator I = begin(); I != end(); ++I) {
 205     OS << '\t';
 206     I->print(OS, &getParent()->getTarget());
 207   }
 208
 209   // Print the successors of this block according to the CFG.
 210   if (!succ_empty()) {
 211     OS << "    Successors according to CFG:";
 212     for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
 213       OS << ' ' << *SI << " (#" << (*SI)->getNumber() << ')';
 214     OS << '\n';
 215   }
 216 }
 217
 218 void MachineBasicBlock::removeLiveIn(unsigned Reg) {
 219   livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
 220   assert(I != livein_end() && "Not a live in!");
 221   LiveIns.erase(I);
 222 }
 223
 224 bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
 225   const_livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
 226   return I != livein_end();
 227 }
 228
 229 void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
 230   getParent()->splice(NewAfter, this);
 231 }
 232
 233 void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
 234   MachineFunction::iterator BBI = NewBefore;
 235   getParent()->splice(++BBI, this);
 236 }
 237
 238
 239 void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
 240   Successors.push_back(succ);
 241   succ->addPredecessor(this);
 242 }
 243
 244 void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
 245   succ->removePredecessor(this);
 246   succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
 247   assert(I != Successors.end() && "Not a current successor!");
 248   Successors.erase(I);
 249 }
 250
 251 MachineBasicBlock::succ_iterator
 252 MachineBasicBlock::removeSuccessor(succ_iterator I) {
 253   assert(I != Successors.end() && "Not a current successor!");
 254   (*I)->removePredecessor(this);
 255   return Successors.erase(I);
 256 }
 257
 258 void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
 259   Predecessors.push_back(pred);
 260 }
 261
 262 void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
 263   std::vector<MachineBasicBlock *>::iterator I =
 264     std::find(Predecessors.begin(), Predecessors.end(), pred);
 265   assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
 266   Predecessors.erase(I);
 267 }
 268
 269 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *fromMBB) {
 270   if (this == fromMBB)
 271     return;
 272
 273   for (MachineBasicBlock::succ_iterator I = fromMBB->succ_begin(),
 274        E = fromMBB->succ_end(); I != E; ++I)
 275     addSuccessor(*I);
 276
 277   while (!fromMBB->succ_empty())
 278     fromMBB->removeSuccessor(fromMBB->succ_begin());
 279 }
 280
 281 bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
 282   std::vector<MachineBasicBlock *>::const_iterator I =
 283     std::find(Successors.begin(), Successors.end(), MBB);
 284   return I != Successors.end();
 285 }
 286
 287 bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
 288   MachineFunction::const_iterator I(this);
 289   return next(I) == MachineFunction::const_iterator(MBB);
 290 }
 291
 292 /// removeFromParent - This method unlinks 'this' from the containing function,
 293 /// and returns it, but does not delete it.
 294 MachineBasicBlock *MachineBasicBlock::removeFromParent() {
 295   assert(getParent() && "Not embedded in a function!");
 296   getParent()->remove(this);
 297   return this;
 298 }
 299
 300
 301 /// eraseFromParent - This method unlinks 'this' from the containing function,
 302 /// and deletes it.
 303 void MachineBasicBlock::eraseFromParent() {
 304   assert(getParent() && "Not embedded in a function!");
 305   getParent()->erase(this);
 306 }
 307
 308
 309 /// ReplaceUsesOfBlockWith - Given a machine basic block that branched to
 310 /// 'Old', change the code and CFG so that it branches to 'New' instead.
 311 void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
 312                                                MachineBasicBlock *New) {
 313   assert(Old != New && "Cannot replace self with self!");
 314
 315   MachineBasicBlock::iterator I = end();
 316   while (I != begin()) {
 317     --I;
 318     if (!I->getDesc().isTerminator()) break;
 319
 320     // Scan the operands of this machine instruction, replacing any uses of Old
 321     // with New.
 322     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
 323       if (I->getOperand(i).isMBB() &&
 324           I->getOperand(i).getMBB() == Old)
 325         I->getOperand(i).setMBB(New);
 326   }
 327
 328   // Update the successor information.
 329   removeSuccessor(Old);
 330   addSuccessor(New);
 331 }
 332
 333 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
 334 /// CFG to be inserted.  If we have proven that MBB can only branch to DestA and
 335 /// DestB, remove any other MBB successors from the CFG.  DestA and DestB can
 336 /// be null.
 337 /// Besides DestA and DestB, retain other edges leading to LandingPads
 338 /// (currently there can be only one; we don't check or require that here).
 339 /// Note it is possible that DestA and/or DestB are LandingPads.
 340 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
 341                                              MachineBasicBlock *DestB,
 342                                              bool isCond) {
 343   bool MadeChange = false;
 344   bool AddedFallThrough = false;
 345
 346   MachineFunction::iterator FallThru = next(MachineFunction::iterator(this));
 347
 348   // If this block ends with a conditional branch that falls through to its
 349   // successor, set DestB as the successor.
 350   if (isCond) {
 351     if (DestB == 0 && FallThru != getParent()->end()) {
 352       DestB = FallThru;
 353       AddedFallThrough = true;
 354     }
 355   } else {
 356     // If this is an unconditional branch with no explicit dest, it must just be
 357     // a fallthrough into DestB.
 358     if (DestA == 0 && FallThru != getParent()->end()) {
 359       DestA = FallThru;
 360       AddedFallThrough = true;
 361     }
 362   }
 363
 364   MachineBasicBlock::succ_iterator SI = succ_begin();
 365   MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB;
 366   while (SI != succ_end()) {
 367     if (*SI == DestA && DestA == DestB) {
 368       DestA = DestB = 0;
 369       ++SI;
 370     } else if (*SI == DestA) {
 371       DestA = 0;
 372       ++SI;
 373     } else if (*SI == DestB) {
 374       DestB = 0;
 375       ++SI;
 376     } else if ((*SI)->isLandingPad() &&
 377                *SI!=OrigDestA && *SI!=OrigDestB) {
 378       ++SI;
 379     } else {
 380       // Otherwise, this is a superfluous edge, remove it.
 381       SI = removeSuccessor(SI);
 382       MadeChange = true;
 383     }
 384   }
 385   if (!AddedFallThrough) {
 386     assert(DestA == 0 && DestB == 0 &&
 387            "MachineCFG is missing edges!");
 388   } else if (isCond) {
 389     assert(DestA == 0 && "MachineCFG is missing edges!");
 390   }
 391   return MadeChange;
 392 }