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