lib/Analysis/PHITransAddr.cpp

   1 //===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
   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 file implements the PHITransAddr class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/PHITransAddr.h"
  15 #include "llvm/Constants.h"
  16 #include "llvm/Instructions.h"
  17 #include "llvm/Analysis/Dominators.h"
  18 #include "llvm/Analysis/InstructionSimplify.h"
  19 #include "llvm/Support/Debug.h"
  20 #include "llvm/Support/ErrorHandling.h"
  21 #include "llvm/Support/raw_ostream.h"
  22 using namespace llvm;
  23
  24 static bool CanPHITrans(Instruction *Inst) {
  25   if (isa<PHINode>(Inst) ||
  26       isa<GetElementPtrInst>(Inst))
  27     return true;
  28
  29   if (isa<CastInst>(Inst) &&
  30       Inst->isSafeToSpeculativelyExecute())
  31     return true;
  32
  33   if (Inst->getOpcode() == Instruction::Add &&
  34       isa<ConstantInt>(Inst->getOperand(1)))
  35     return true;
  36
  37   //   cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
  38   //   if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
  39   //     cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
  40   return false;
  41 }
  42
  43 void PHITransAddr::dump() const {
  44   if (Addr == 0) {
  45     dbgs() << "PHITransAddr: null\n";
  46     return;
  47   }
  48   dbgs() << "PHITransAddr: " << *Addr << "\n";
  49   for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
  50     dbgs() << "  Input #" << i << " is " << *InstInputs[i] << "\n";
  51 }
  52
  53
  54 static bool VerifySubExpr(Value *Expr,
  55                           SmallVectorImpl<Instruction*> &InstInputs) {
  56   // If this is a non-instruction value, there is nothing to do.
  57   Instruction *I = dyn_cast<Instruction>(Expr);
  58   if (I == 0) return true;
  59
  60   // If it's an instruction, it is either in Tmp or its operands recursively
  61   // are.
  62   SmallVectorImpl<Instruction*>::iterator Entry =
  63     std::find(InstInputs.begin(), InstInputs.end(), I);
  64   if (Entry != InstInputs.end()) {
  65     InstInputs.erase(Entry);
  66     return true;
  67   }
  68
  69   // If it isn't in the InstInputs list it is a subexpr incorporated into the
  70   // address.  Sanity check that it is phi translatable.
  71   if (!CanPHITrans(I)) {
  72     errs() << "Non phi translatable instruction found in PHITransAddr:\n";
  73     errs() << *I << '\n';
  74     llvm_unreachable("Either something is missing from InstInputs or "
  75                      "CanPHITrans is wrong.");
  76     return false;
  77   }
  78
  79   // Validate the operands of the instruction.
  80   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
  81     if (!VerifySubExpr(I->getOperand(i), InstInputs))
  82       return false;
  83
  84   return true;
  85 }
  86
  87 /// Verify - Check internal consistency of this data structure.  If the
  88 /// structure is valid, it returns true.  If invalid, it prints errors and
  89 /// returns false.
  90 bool PHITransAddr::Verify() const {
  91   if (Addr == 0) return true;
  92
  93   SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
  94
  95   if (!VerifySubExpr(Addr, Tmp))
  96     return false;
  97
  98   if (!Tmp.empty()) {
  99     errs() << "PHITransAddr contains extra instructions:\n";
 100     for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
 101       errs() << "  InstInput #" << i << " is " << *InstInputs[i] << "\n";
 102     llvm_unreachable("This is unexpected.");
 103     return false;
 104   }
 105
 106   // a-ok.
 107   return true;
 108 }
 109
 110
 111 /// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
 112 /// if we have some hope of doing it.  This should be used as a filter to
 113 /// avoid calling PHITranslateValue in hopeless situations.
 114 bool PHITransAddr::IsPotentiallyPHITranslatable() const {
 115   // If the input value is not an instruction, or if it is not defined in CurBB,
 116   // then we don't need to phi translate it.
 117   Instruction *Inst = dyn_cast<Instruction>(Addr);
 118   return Inst == 0 || CanPHITrans(Inst);
 119 }
 120
 121
 122 static void RemoveInstInputs(Value *V,
 123                              SmallVectorImpl<Instruction*> &InstInputs) {
 124   Instruction *I = dyn_cast<Instruction>(V);
 125   if (I == 0) return;
 126
 127   // If the instruction is in the InstInputs list, remove it.
 128   SmallVectorImpl<Instruction*>::iterator Entry =
 129     std::find(InstInputs.begin(), InstInputs.end(), I);
 130   if (Entry != InstInputs.end()) {
 131     InstInputs.erase(Entry);
 132     return;
 133   }
 134
 135   assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
 136
 137   // Otherwise, it must have instruction inputs itself.  Zap them recursively.
 138   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
 139     if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
 140       RemoveInstInputs(Op, InstInputs);
 141   }
 142 }
 143
 144 Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
 145                                          BasicBlock *PredBB,
 146                                          const DominatorTree *DT) {
 147   // If this is a non-instruction value, it can't require PHI translation.
 148   Instruction *Inst = dyn_cast<Instruction>(V);
 149   if (Inst == 0) return V;
 150
 151   // Determine whether 'Inst' is an input to our PHI translatable expression.
 152   bool isInput = std::count(InstInputs.begin(), InstInputs.end(), Inst);
 153
 154   // Handle inputs instructions if needed.
 155   if (isInput) {
 156     if (Inst->getParent() != CurBB) {
 157       // If it is an input defined in a different block, then it remains an
 158       // input.
 159       return Inst;
 160     }
 161
 162     // If 'Inst' is defined in this block and is an input that needs to be phi
 163     // translated, we need to incorporate the value into the expression or fail.
 164
 165     // In either case, the instruction itself isn't an input any longer.
 166     InstInputs.erase(std::find(InstInputs.begin(), InstInputs.end(), Inst));
 167
 168     // If this is a PHI, go ahead and translate it.
 169     if (PHINode *PN = dyn_cast<PHINode>(Inst))
 170       return AddAsInput(PN->getIncomingValueForBlock(PredBB));
 171
 172     // If this is a non-phi value, and it is analyzable, we can incorporate it
 173     // into the expression by making all instruction operands be inputs.
 174     if (!CanPHITrans(Inst))
 175       return 0;
 176
 177     // All instruction operands are now inputs (and of course, they may also be
 178     // defined in this block, so they may need to be phi translated themselves.
 179     for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
 180       if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
 181         InstInputs.push_back(Op);
 182   }
 183
 184   // Ok, it must be an intermediate result (either because it started that way
 185   // or because we just incorporated it into the expression).  See if its
 186   // operands need to be phi translated, and if so, reconstruct it.
 187
 188   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
 189     if (!Cast->isSafeToSpeculativelyExecute()) return 0;
 190     Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
 191     if (PHIIn == 0) return 0;
 192     if (PHIIn == Cast->getOperand(0))
 193       return Cast;
 194
 195     // Find an available version of this cast.
 196
 197     // Constants are trivial to find.
 198     if (Constant *C = dyn_cast<Constant>(PHIIn))
 199       return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
 200                                               C, Cast->getType()));
 201
 202     // Otherwise we have to see if a casted version of the incoming pointer
 203     // is available.  If so, we can use it, otherwise we have to fail.
 204     for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
 205          UI != E; ++UI) {
 206       if (CastInst *CastI = dyn_cast<CastInst>(*UI))
 207         if (CastI->getOpcode() == Cast->getOpcode() &&
 208             CastI->getType() == Cast->getType() &&
 209             (!DT || DT->dominates(CastI->getParent(), PredBB)))
 210           return CastI;
 211     }
 212     return 0;
 213   }
 214
 215   // Handle getelementptr with at least one PHI translatable operand.
 216   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
 217     SmallVector<Value*, 8> GEPOps;
 218     bool AnyChanged = false;
 219     for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
 220       Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
 221       if (GEPOp == 0) return 0;
 222
 223       AnyChanged |= GEPOp != GEP->getOperand(i);
 224       GEPOps.push_back(GEPOp);
 225     }
 226
 227     if (!AnyChanged)
 228       return GEP;
 229
 230     // Simplify the GEP to handle 'gep x, 0' -> x etc.
 231     if (Value *V = SimplifyGEPInst(&GEPOps[0], GEPOps.size(), TD, DT)) {
 232       for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
 233         RemoveInstInputs(GEPOps[i], InstInputs);
 234
 235       return AddAsInput(V);
 236     }
 237
 238     // Scan to see if we have this GEP available.
 239     Value *APHIOp = GEPOps[0];
 240     for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
 241          UI != E; ++UI) {
 242       if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
 243         if (GEPI->getType() == GEP->getType() &&
 244             GEPI->getNumOperands() == GEPOps.size() &&
 245             GEPI->getParent()->getParent() == CurBB->getParent() &&
 246             (!DT || DT->dominates(GEPI->getParent(), PredBB))) {
 247           bool Mismatch = false;
 248           for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
 249             if (GEPI->getOperand(i) != GEPOps[i]) {
 250               Mismatch = true;
 251               break;
 252             }
 253           if (!Mismatch)
 254             return GEPI;
 255         }
 256     }
 257     return 0;
 258   }
 259
 260   // Handle add with a constant RHS.
 261   if (Inst->getOpcode() == Instruction::Add &&
 262       isa<ConstantInt>(Inst->getOperand(1))) {
 263     // PHI translate the LHS.
 264     Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
 265     bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
 266     bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
 267
 268     Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
 269     if (LHS == 0) return 0;
 270
 271     // If the PHI translated LHS is an add of a constant, fold the immediates.
 272     if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
 273       if (BOp->getOpcode() == Instruction::Add)
 274         if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
 275           LHS = BOp->getOperand(0);
 276           RHS = ConstantExpr::getAdd(RHS, CI);
 277           isNSW = isNUW = false;
 278
 279           // If the old 'LHS' was an input, add the new 'LHS' as an input.
 280           if (std::count(InstInputs.begin(), InstInputs.end(), BOp)) {
 281             RemoveInstInputs(BOp, InstInputs);
 282             AddAsInput(LHS);
 283           }
 284         }
 285
 286     // See if the add simplifies away.
 287     if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, TD, DT)) {
 288       // If we simplified the operands, the LHS is no longer an input, but Res
 289       // is.
 290       RemoveInstInputs(LHS, InstInputs);
 291       return AddAsInput(Res);
 292     }
 293
 294     // If we didn't modify the add, just return it.
 295     if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
 296       return Inst;
 297
 298     // Otherwise, see if we have this add available somewhere.
 299     for (Value::use_iterator UI = LHS->use_begin(), E = LHS->use_end();
 300          UI != E; ++UI) {
 301       if (BinaryOperator *BO = dyn_cast<BinaryOperator>(*UI))
 302         if (BO->getOpcode() == Instruction::Add &&
 303             BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
 304             BO->getParent()->getParent() == CurBB->getParent() &&
 305             (!DT || DT->dominates(BO->getParent(), PredBB)))
 306           return BO;
 307     }
 308
 309     return 0;
 310   }
 311
 312   // Otherwise, we failed.
 313   return 0;
 314 }
 315
 316
 317 /// PHITranslateValue - PHI translate the current address up the CFG from
 318 /// CurBB to Pred, updating our state to reflect any needed changes.  If the
 319 /// dominator tree DT is non-null, the translated value must dominate
 320 /// PredBB.  This returns true on failure and sets Addr to null.
 321 bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
 322                                      const DominatorTree *DT) {
 323   assert(Verify() && "Invalid PHITransAddr!");
 324   Addr = PHITranslateSubExpr(Addr, CurBB, PredBB, DT);
 325   assert(Verify() && "Invalid PHITransAddr!");
 326
 327   if (DT) {
 328     // Make sure the value is live in the predecessor.
 329     if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
 330       if (!DT->dominates(Inst->getParent(), PredBB))
 331         Addr = 0;
 332   }
 333
 334   return Addr == 0;
 335 }
 336
 337 /// PHITranslateWithInsertion - PHI translate this value into the specified
 338 /// predecessor block, inserting a computation of the value if it is
 339 /// unavailable.
 340 ///
 341 /// All newly created instructions are added to the NewInsts list.  This
 342 /// returns null on failure.
 343 ///
 344 Value *PHITransAddr::
 345 PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
 346                           const DominatorTree &DT,
 347                           SmallVectorImpl<Instruction*> &NewInsts) {
 348   unsigned NISize = NewInsts.size();
 349
 350   // Attempt to PHI translate with insertion.
 351   Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
 352
 353   // If successful, return the new value.
 354   if (Addr) return Addr;
 355
 356   // If not, destroy any intermediate instructions inserted.
 357   while (NewInsts.size() != NISize)
 358     NewInsts.pop_back_val()->eraseFromParent();
 359   return 0;
 360 }
 361
 362
 363 /// InsertPHITranslatedPointer - Insert a computation of the PHI translated
 364 /// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
 365 /// block.  All newly created instructions are added to the NewInsts list.
 366 /// This returns null on failure.
 367 ///
 368 Value *PHITransAddr::
 369 InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
 370                            BasicBlock *PredBB, const DominatorTree &DT,
 371                            SmallVectorImpl<Instruction*> &NewInsts) {
 372   // See if we have a version of this value already available and dominating
 373   // PredBB.  If so, there is no need to insert a new instance of it.
 374   PHITransAddr Tmp(InVal, TD);
 375   if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT))
 376     return Tmp.getAddr();
 377
 378   // If we don't have an available version of this value, it must be an
 379   // instruction.
 380   Instruction *Inst = cast<Instruction>(InVal);
 381
 382   // Handle cast of PHI translatable value.
 383   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
 384     if (!Cast->isSafeToSpeculativelyExecute()) return 0;
 385     Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
 386                                               CurBB, PredBB, DT, NewInsts);
 387     if (OpVal == 0) return 0;
 388
 389     // Otherwise insert a cast at the end of PredBB.
 390     CastInst *New = CastInst::Create(Cast->getOpcode(),
 391                                      OpVal, InVal->getType(),
 392                                      InVal->getName()+".phi.trans.insert",
 393                                      PredBB->getTerminator());
 394     NewInsts.push_back(New);
 395     return New;
 396   }
 397
 398   // Handle getelementptr with at least one PHI operand.
 399   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
 400     SmallVector<Value*, 8> GEPOps;
 401     BasicBlock *CurBB = GEP->getParent();
 402     for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
 403       Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
 404                                                 CurBB, PredBB, DT, NewInsts);
 405       if (OpVal == 0) return 0;
 406       GEPOps.push_back(OpVal);
 407     }
 408
 409     GetElementPtrInst *Result =
 410     GetElementPtrInst::Create(GEPOps[0], GEPOps.begin()+1, GEPOps.end(),
 411                               InVal->getName()+".phi.trans.insert",
 412                               PredBB->getTerminator());
 413     Result->setIsInBounds(GEP->isInBounds());
 414     NewInsts.push_back(Result);
 415     return Result;
 416   }
 417
 418 #if 0
 419   // FIXME: This code works, but it is unclear that we actually want to insert
 420   // a big chain of computation in order to make a value available in a block.
 421   // This needs to be evaluated carefully to consider its cost trade offs.
 422
 423   // Handle add with a constant RHS.
 424   if (Inst->getOpcode() == Instruction::Add &&
 425       isa<ConstantInt>(Inst->getOperand(1))) {
 426     // PHI translate the LHS.
 427     Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
 428                                               CurBB, PredBB, DT, NewInsts);
 429     if (OpVal == 0) return 0;
 430
 431     BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
 432                                            InVal->getName()+".phi.trans.insert",
 433                                                     PredBB->getTerminator());
 434     Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
 435     Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
 436     NewInsts.push_back(Res);
 437     return Res;
 438   }
 439 #endif
 440
 441   return 0;
 442 }