lib/Analysis/PHITransAddr.cpp

   1 //===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the PHITransAddr class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Analysis/PHITransAddr.h"
  14 #include "llvm/Analysis/InstructionSimplify.h"
  15 #include "llvm/Analysis/ValueTracking.h"
  16 #include "llvm/Config/llvm-config.h"
  17 #include "llvm/IR/Constants.h"
  18 #include "llvm/IR/Dominators.h"
  19 #include "llvm/IR/Instructions.h"
  20 #include "llvm/Support/Debug.h"
  21 #include "llvm/Support/ErrorHandling.h"
  22 #include "llvm/Support/raw_ostream.h"
  23 using namespace llvm;
  24
  25 static bool CanPHITrans(Instruction *Inst) {
  26   if (isa<PHINode>(Inst) ||
  27       isa<GetElementPtrInst>(Inst))
  28     return true;
  29
  30   if (isa<CastInst>(Inst) &&
  31       isSafeToSpeculativelyExecute(Inst))
  32     return true;
  33
  34   if (Inst->getOpcode() == Instruction::Add &&
  35       isa<ConstantInt>(Inst->getOperand(1)))
  36     return true;
  37
  38   //   cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
  39   //   if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
  40   //     cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
  41   return false;
  42 }
  43
  44 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  45 LLVM_DUMP_METHOD void PHITransAddr::dump() const {
  46   if (!Addr) {
  47     dbgs() << "PHITransAddr: null\n";
  48     return;
  49   }
  50   dbgs() << "PHITransAddr: " << *Addr << "\n";
  51   for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
  52     dbgs() << "  Input #" << i << " is " << *InstInputs[i] << "\n";
  53 }
  54 #endif
  55
  56
  57 static bool VerifySubExpr(Value *Expr,
  58                           SmallVectorImpl<Instruction*> &InstInputs) {
  59   // If this is a non-instruction value, there is nothing to do.
  60   Instruction *I = dyn_cast<Instruction>(Expr);
  61   if (!I) return true;
  62
  63   // If it's an instruction, it is either in Tmp or its operands recursively
  64   // are.
  65   SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
  66   if (Entry != InstInputs.end()) {
  67     InstInputs.erase(Entry);
  68     return true;
  69   }
  70
  71   // If it isn't in the InstInputs list it is a subexpr incorporated into the
  72   // address.  Sanity check that it is phi translatable.
  73   if (!CanPHITrans(I)) {
  74     errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
  75     errs() << *I << '\n';
  76     llvm_unreachable("Either something is missing from InstInputs or "
  77                      "CanPHITrans is wrong.");
  78   }
  79
  80   // Validate the operands of the instruction.
  81   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
  82     if (!VerifySubExpr(I->getOperand(i), InstInputs))
  83       return false;
  84
  85   return true;
  86 }
  87
  88 /// Verify - Check internal consistency of this data structure.  If the
  89 /// structure is valid, it returns true.  If invalid, it prints errors and
  90 /// returns false.
  91 bool PHITransAddr::Verify() const {
  92   if (!Addr) return true;
  93
  94   SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
  95
  96   if (!VerifySubExpr(Addr, Tmp))
  97     return false;
  98
  99   if (!Tmp.empty()) {
 100     errs() << "PHITransAddr contains extra instructions:\n";
 101     for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
 102       errs() << "  InstInput #" << i << " is " << *InstInputs[i] << "\n";
 103     llvm_unreachable("This is unexpected.");
 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 || 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) return;
 126
 127   // If the instruction is in the InstInputs list, remove it.
 128   SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
 129   if (Entry != InstInputs.end()) {
 130     InstInputs.erase(Entry);
 131     return;
 132   }
 133
 134   assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
 135
 136   // Otherwise, it must have instruction inputs itself.  Zap them recursively.
 137   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
 138     if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
 139       RemoveInstInputs(Op, InstInputs);
 140   }
 141 }
 142
 143 Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
 144                                          BasicBlock *PredBB,
 145                                          const DominatorTree *DT) {
 146   // If this is a non-instruction value, it can't require PHI translation.
 147   Instruction *Inst = dyn_cast<Instruction>(V);
 148   if (!Inst) return V;
 149
 150   // Determine whether 'Inst' is an input to our PHI translatable expression.
 151   bool isInput = is_contained(InstInputs, Inst);
 152
 153   // Handle inputs instructions if needed.
 154   if (isInput) {
 155     if (Inst->getParent() != CurBB) {
 156       // If it is an input defined in a different block, then it remains an
 157       // input.
 158       return Inst;
 159     }
 160
 161     // If 'Inst' is defined in this block and is an input that needs to be phi
 162     // translated, we need to incorporate the value into the expression or fail.
 163
 164     // In either case, the instruction itself isn't an input any longer.
 165     InstInputs.erase(find(InstInputs, Inst));
 166
 167     // If this is a PHI, go ahead and translate it.
 168     if (PHINode *PN = dyn_cast<PHINode>(Inst))
 169       return AddAsInput(PN->getIncomingValueForBlock(PredBB));
 170
 171     // If this is a non-phi value, and it is analyzable, we can incorporate it
 172     // into the expression by making all instruction operands be inputs.
 173     if (!CanPHITrans(Inst))
 174       return nullptr;
 175
 176     // All instruction operands are now inputs (and of course, they may also be
 177     // defined in this block, so they may need to be phi translated themselves.
 178     for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
 179       if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
 180         InstInputs.push_back(Op);
 181   }
 182
 183   // Ok, it must be an intermediate result (either because it started that way
 184   // or because we just incorporated it into the expression).  See if its
 185   // operands need to be phi translated, and if so, reconstruct it.
 186
 187   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
 188     if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
 189     Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
 190     if (!PHIIn) return nullptr;
 191     if (PHIIn == Cast->getOperand(0))
 192       return Cast;
 193
 194     // Find an available version of this cast.
 195
 196     // Constants are trivial to find.
 197     if (Constant *C = dyn_cast<Constant>(PHIIn))
 198       return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
 199                                               C, Cast->getType()));
 200
 201     // Otherwise we have to see if a casted version of the incoming pointer
 202     // is available.  If so, we can use it, otherwise we have to fail.
 203     for (User *U : PHIIn->users()) {
 204       if (CastInst *CastI = dyn_cast<CastInst>(U))
 205         if (CastI->getOpcode() == Cast->getOpcode() &&
 206             CastI->getType() == Cast->getType() &&
 207             (!DT || DT->dominates(CastI->getParent(), PredBB)))
 208           return CastI;
 209     }
 210     return nullptr;
 211   }
 212
 213   // Handle getelementptr with at least one PHI translatable operand.
 214   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
 215     SmallVector<Value*, 8> GEPOps;
 216     bool AnyChanged = false;
 217     for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
 218       Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
 219       if (!GEPOp) return nullptr;
 220
 221       AnyChanged |= GEPOp != GEP->getOperand(i);
 222       GEPOps.push_back(GEPOp);
 223     }
 224
 225     if (!AnyChanged)
 226       return GEP;
 227
 228     // Simplify the GEP to handle 'gep x, 0' -> x etc.
 229     if (Value *V = SimplifyGEPInst(GEP->getSourceElementType(),
 230                                    GEPOps, {DL, TLI, DT, AC})) {
 231       for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
 232         RemoveInstInputs(GEPOps[i], InstInputs);
 233
 234       return AddAsInput(V);
 235     }
 236
 237     // Scan to see if we have this GEP available.
 238     Value *APHIOp = GEPOps[0];
 239     for (User *U : APHIOp->users()) {
 240       if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
 241         if (GEPI->getType() == GEP->getType() &&
 242             GEPI->getNumOperands() == GEPOps.size() &&
 243             GEPI->getParent()->getParent() == CurBB->getParent() &&
 244             (!DT || DT->dominates(GEPI->getParent(), PredBB))) {
 245           if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
 246             return GEPI;
 247         }
 248     }
 249     return nullptr;
 250   }
 251
 252   // Handle add with a constant RHS.
 253   if (Inst->getOpcode() == Instruction::Add &&
 254       isa<ConstantInt>(Inst->getOperand(1))) {
 255     // PHI translate the LHS.
 256     Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
 257     bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
 258     bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
 259
 260     Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
 261     if (!LHS) return nullptr;
 262
 263     // If the PHI translated LHS is an add of a constant, fold the immediates.
 264     if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
 265       if (BOp->getOpcode() == Instruction::Add)
 266         if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
 267           LHS = BOp->getOperand(0);
 268           RHS = ConstantExpr::getAdd(RHS, CI);
 269           isNSW = isNUW = false;
 270
 271           // If the old 'LHS' was an input, add the new 'LHS' as an input.
 272           if (is_contained(InstInputs, BOp)) {
 273             RemoveInstInputs(BOp, InstInputs);
 274             AddAsInput(LHS);
 275           }
 276         }
 277
 278     // See if the add simplifies away.
 279     if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
 280       // If we simplified the operands, the LHS is no longer an input, but Res
 281       // is.
 282       RemoveInstInputs(LHS, InstInputs);
 283       return AddAsInput(Res);
 284     }
 285
 286     // If we didn't modify the add, just return it.
 287     if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
 288       return Inst;
 289
 290     // Otherwise, see if we have this add available somewhere.
 291     for (User *U : LHS->users()) {
 292       if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
 293         if (BO->getOpcode() == Instruction::Add &&
 294             BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
 295             BO->getParent()->getParent() == CurBB->getParent() &&
 296             (!DT || DT->dominates(BO->getParent(), PredBB)))
 297           return BO;
 298     }
 299
 300     return nullptr;
 301   }
 302
 303   // Otherwise, we failed.
 304   return nullptr;
 305 }
 306
 307
 308 /// PHITranslateValue - PHI translate the current address up the CFG from
 309 /// CurBB to Pred, updating our state to reflect any needed changes.  If
 310 /// 'MustDominate' is true, the translated value must dominate
 311 /// PredBB.  This returns true on failure and sets Addr to null.
 312 bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
 313                                      const DominatorTree *DT,
 314                                      bool MustDominate) {
 315   assert(DT || !MustDominate);
 316   assert(Verify() && "Invalid PHITransAddr!");
 317   if (DT && DT->isReachableFromEntry(PredBB))
 318     Addr =
 319         PHITranslateSubExpr(Addr, CurBB, PredBB, MustDominate ? DT : nullptr);
 320   else
 321     Addr = nullptr;
 322   assert(Verify() && "Invalid PHITransAddr!");
 323
 324   if (MustDominate)
 325     // Make sure the value is live in the predecessor.
 326     if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
 327       if (!DT->dominates(Inst->getParent(), PredBB))
 328         Addr = nullptr;
 329
 330   return Addr == nullptr;
 331 }
 332
 333 /// PHITranslateWithInsertion - PHI translate this value into the specified
 334 /// predecessor block, inserting a computation of the value if it is
 335 /// unavailable.
 336 ///
 337 /// All newly created instructions are added to the NewInsts list.  This
 338 /// returns null on failure.
 339 ///
 340 Value *PHITransAddr::
 341 PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
 342                           const DominatorTree &DT,
 343                           SmallVectorImpl<Instruction*> &NewInsts) {
 344   unsigned NISize = NewInsts.size();
 345
 346   // Attempt to PHI translate with insertion.
 347   Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
 348
 349   // If successful, return the new value.
 350   if (Addr) return Addr;
 351
 352   // If not, destroy any intermediate instructions inserted.
 353   while (NewInsts.size() != NISize)
 354     NewInsts.pop_back_val()->eraseFromParent();
 355   return nullptr;
 356 }
 357
 358
 359 /// InsertPHITranslatedPointer - Insert a computation of the PHI translated
 360 /// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
 361 /// block.  All newly created instructions are added to the NewInsts list.
 362 /// This returns null on failure.
 363 ///
 364 Value *PHITransAddr::
 365 InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
 366                            BasicBlock *PredBB, const DominatorTree &DT,
 367                            SmallVectorImpl<Instruction*> &NewInsts) {
 368   // See if we have a version of this value already available and dominating
 369   // PredBB.  If so, there is no need to insert a new instance of it.
 370   PHITransAddr Tmp(InVal, DL, AC);
 371   if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
 372     return Tmp.getAddr();
 373
 374   // We don't need to PHI translate values which aren't instructions.
 375   auto *Inst = dyn_cast<Instruction>(InVal);
 376   if (!Inst)
 377     return nullptr;
 378
 379   // Handle cast of PHI translatable value.
 380   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
 381     if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
 382     Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
 383                                               CurBB, PredBB, DT, NewInsts);
 384     if (!OpVal) return nullptr;
 385
 386     // Otherwise insert a cast at the end of PredBB.
 387     CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
 388                                      InVal->getName() + ".phi.trans.insert",
 389                                      PredBB->getTerminator());
 390     New->setDebugLoc(Inst->getDebugLoc());
 391     NewInsts.push_back(New);
 392     return New;
 393   }
 394
 395   // Handle getelementptr with at least one PHI operand.
 396   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
 397     SmallVector<Value*, 8> GEPOps;
 398     BasicBlock *CurBB = GEP->getParent();
 399     for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
 400       Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
 401                                                 CurBB, PredBB, DT, NewInsts);
 402       if (!OpVal) return nullptr;
 403       GEPOps.push_back(OpVal);
 404     }
 405
 406     GetElementPtrInst *Result = GetElementPtrInst::Create(
 407         GEP->getSourceElementType(), GEPOps[0], makeArrayRef(GEPOps).slice(1),
 408         InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
 409     Result->setDebugLoc(Inst->getDebugLoc());
 410     Result->setIsInBounds(GEP->isInBounds());
 411     NewInsts.push_back(Result);
 412     return Result;
 413   }
 414
 415 #if 0
 416   // FIXME: This code works, but it is unclear that we actually want to insert
 417   // a big chain of computation in order to make a value available in a block.
 418   // This needs to be evaluated carefully to consider its cost trade offs.
 419
 420   // Handle add with a constant RHS.
 421   if (Inst->getOpcode() == Instruction::Add &&
 422       isa<ConstantInt>(Inst->getOperand(1))) {
 423     // PHI translate the LHS.
 424     Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
 425                                               CurBB, PredBB, DT, NewInsts);
 426     if (OpVal == 0) return 0;
 427
 428     BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
 429                                            InVal->getName()+".phi.trans.insert",
 430                                                     PredBB->getTerminator());
 431     Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
 432     Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
 433     NewInsts.push_back(Res);
 434     return Res;
 435   }
 436 #endif
 437
 438   return nullptr;
 439 }