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