1 //===- InstCombinePHI.cpp -------------------------------------------------===// 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 visitPHINode function. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "InstCombineInternal.h" 15 #include "llvm/ADT/STLExtras.h" 16 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/Analysis/InstructionSimplify.h" 18 #include "llvm/Transforms/Utils/Local.h" 19 #include "llvm/Analysis/ValueTracking.h" 20 #include "llvm/IR/PatternMatch.h" 21 using namespace llvm; 22 using namespace llvm::PatternMatch; 23 24 #define DEBUG_TYPE "instcombine" 25 26 static cl::opt<unsigned> 27 MaxNumPhis("instcombine-max-num-phis", cl::init(512), 28 cl::desc("Maximum number phis to handle in intptr/ptrint folding")); 29 30 /// The PHI arguments will be folded into a single operation with a PHI node 31 /// as input. The debug location of the single operation will be the merged 32 /// locations of the original PHI node arguments. 33 void InstCombiner::PHIArgMergedDebugLoc(Instruction *Inst, PHINode &PN) { 34 auto *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 35 Inst->setDebugLoc(FirstInst->getDebugLoc()); 36 // We do not expect a CallInst here, otherwise, N-way merging of DebugLoc 37 // will be inefficient. 38 assert(!isa<CallInst>(Inst)); 39 40 for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 41 auto *I = cast<Instruction>(PN.getIncomingValue(i)); 42 Inst->applyMergedLocation(Inst->getDebugLoc(), I->getDebugLoc()); 43 } 44 } 45 46 // Replace Integer typed PHI PN if the PHI's value is used as a pointer value. 47 // If there is an existing pointer typed PHI that produces the same value as PN, 48 // replace PN and the IntToPtr operation with it. Otherwise, synthesize a new 49 // PHI node: 50 // 51 // Case-1: 52 // bb1: 53 // int_init = PtrToInt(ptr_init) 54 // br label %bb2 55 // bb2: 56 // int_val = PHI([int_init, %bb1], [int_val_inc, %bb2] 57 // ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] 58 // ptr_val2 = IntToPtr(int_val) 59 // ... 60 // use(ptr_val2) 61 // ptr_val_inc = ... 62 // inc_val_inc = PtrToInt(ptr_val_inc) 63 // 64 // ==> 65 // bb1: 66 // br label %bb2 67 // bb2: 68 // ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] 69 // ... 70 // use(ptr_val) 71 // ptr_val_inc = ... 72 // 73 // Case-2: 74 // bb1: 75 // int_ptr = BitCast(ptr_ptr) 76 // int_init = Load(int_ptr) 77 // br label %bb2 78 // bb2: 79 // int_val = PHI([int_init, %bb1], [int_val_inc, %bb2] 80 // ptr_val2 = IntToPtr(int_val) 81 // ... 82 // use(ptr_val2) 83 // ptr_val_inc = ... 84 // inc_val_inc = PtrToInt(ptr_val_inc) 85 // ==> 86 // bb1: 87 // ptr_init = Load(ptr_ptr) 88 // br label %bb2 89 // bb2: 90 // ptr_val = PHI([ptr_init, %bb1], [ptr_val_inc, %bb2] 91 // ... 92 // use(ptr_val) 93 // ptr_val_inc = ... 94 // ... 95 // 96 Instruction *InstCombiner::FoldIntegerTypedPHI(PHINode &PN) { 97 if (!PN.getType()->isIntegerTy()) 98 return nullptr; 99 if (!PN.hasOneUse()) 100 return nullptr; 101 102 auto *IntToPtr = dyn_cast<IntToPtrInst>(PN.user_back()); 103 if (!IntToPtr) 104 return nullptr; 105 106 // Check if the pointer is actually used as pointer: 107 auto HasPointerUse = [](Instruction *IIP) { 108 for (User *U : IIP->users()) { 109 Value *Ptr = nullptr; 110 if (LoadInst *LoadI = dyn_cast<LoadInst>(U)) { 111 Ptr = LoadI->getPointerOperand(); 112 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 113 Ptr = SI->getPointerOperand(); 114 } else if (GetElementPtrInst *GI = dyn_cast<GetElementPtrInst>(U)) { 115 Ptr = GI->getPointerOperand(); 116 } 117 118 if (Ptr && Ptr == IIP) 119 return true; 120 } 121 return false; 122 }; 123 124 if (!HasPointerUse(IntToPtr)) 125 return nullptr; 126 127 if (DL.getPointerSizeInBits(IntToPtr->getAddressSpace()) != 128 DL.getTypeSizeInBits(IntToPtr->getOperand(0)->getType())) 129 return nullptr; 130 131 SmallVector<Value *, 4> AvailablePtrVals; 132 for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) { 133 Value *Arg = PN.getIncomingValue(i); 134 135 // First look backward: 136 if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) { 137 AvailablePtrVals.emplace_back(PI->getOperand(0)); 138 continue; 139 } 140 141 // Next look forward: 142 Value *ArgIntToPtr = nullptr; 143 for (User *U : Arg->users()) { 144 if (isa<IntToPtrInst>(U) && U->getType() == IntToPtr->getType() && 145 (DT.dominates(cast<Instruction>(U), PN.getIncomingBlock(i)) || 146 cast<Instruction>(U)->getParent() == PN.getIncomingBlock(i))) { 147 ArgIntToPtr = U; 148 break; 149 } 150 } 151 152 if (ArgIntToPtr) { 153 AvailablePtrVals.emplace_back(ArgIntToPtr); 154 continue; 155 } 156 157 // If Arg is defined by a PHI, allow it. This will also create 158 // more opportunities iteratively. 159 if (isa<PHINode>(Arg)) { 160 AvailablePtrVals.emplace_back(Arg); 161 continue; 162 } 163 164 // For a single use integer load: 165 auto *LoadI = dyn_cast<LoadInst>(Arg); 166 if (!LoadI) 167 return nullptr; 168 169 if (!LoadI->hasOneUse()) 170 return nullptr; 171 172 // Push the integer typed Load instruction into the available 173 // value set, and fix it up later when the pointer typed PHI 174 // is synthesized. 175 AvailablePtrVals.emplace_back(LoadI); 176 } 177 178 // Now search for a matching PHI 179 auto *BB = PN.getParent(); 180 assert(AvailablePtrVals.size() == PN.getNumIncomingValues() && 181 "Not enough available ptr typed incoming values"); 182 PHINode *MatchingPtrPHI = nullptr; 183 unsigned NumPhis = 0; 184 for (auto II = BB->begin(), EI = BasicBlock::iterator(BB->getFirstNonPHI()); 185 II != EI; II++, NumPhis++) { 186 // FIXME: consider handling this in AggressiveInstCombine 187 if (NumPhis > MaxNumPhis) 188 return nullptr; 189 PHINode *PtrPHI = dyn_cast<PHINode>(II); 190 if (!PtrPHI || PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType()) 191 continue; 192 MatchingPtrPHI = PtrPHI; 193 for (unsigned i = 0; i != PtrPHI->getNumIncomingValues(); ++i) { 194 if (AvailablePtrVals[i] != 195 PtrPHI->getIncomingValueForBlock(PN.getIncomingBlock(i))) { 196 MatchingPtrPHI = nullptr; 197 break; 198 } 199 } 200 201 if (MatchingPtrPHI) 202 break; 203 } 204 205 if (MatchingPtrPHI) { 206 assert(MatchingPtrPHI->getType() == IntToPtr->getType() && 207 "Phi's Type does not match with IntToPtr"); 208 // The PtrToCast + IntToPtr will be simplified later 209 return CastInst::CreateBitOrPointerCast(MatchingPtrPHI, 210 IntToPtr->getOperand(0)->getType()); 211 } 212 213 // If it requires a conversion for every PHI operand, do not do it. 214 if (std::all_of(AvailablePtrVals.begin(), AvailablePtrVals.end(), 215 [&](Value *V) { 216 return (V->getType() != IntToPtr->getType()) || 217 isa<IntToPtrInst>(V); 218 })) 219 return nullptr; 220 221 // If any of the operand that requires casting is a terminator 222 // instruction, do not do it. 223 if (std::any_of(AvailablePtrVals.begin(), AvailablePtrVals.end(), 224 [&](Value *V) { 225 return (V->getType() != IntToPtr->getType()) && 226 isa<TerminatorInst>(V); 227 })) 228 return nullptr; 229 230 PHINode *NewPtrPHI = PHINode::Create( 231 IntToPtr->getType(), PN.getNumIncomingValues(), PN.getName() + ".ptr"); 232 233 InsertNewInstBefore(NewPtrPHI, PN); 234 SmallDenseMap<Value *, Instruction *> Casts; 235 for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) { 236 auto *IncomingBB = PN.getIncomingBlock(i); 237 auto *IncomingVal = AvailablePtrVals[i]; 238 239 if (IncomingVal->getType() == IntToPtr->getType()) { 240 NewPtrPHI->addIncoming(IncomingVal, IncomingBB); 241 continue; 242 } 243 244 #ifndef NDEBUG 245 LoadInst *LoadI = dyn_cast<LoadInst>(IncomingVal); 246 assert((isa<PHINode>(IncomingVal) || 247 IncomingVal->getType()->isPointerTy() || 248 (LoadI && LoadI->hasOneUse())) && 249 "Can not replace LoadInst with multiple uses"); 250 #endif 251 // Need to insert a BitCast. 252 // For an integer Load instruction with a single use, the load + IntToPtr 253 // cast will be simplified into a pointer load: 254 // %v = load i64, i64* %a.ip, align 8 255 // %v.cast = inttoptr i64 %v to float ** 256 // ==> 257 // %v.ptrp = bitcast i64 * %a.ip to float ** 258 // %v.cast = load float *, float ** %v.ptrp, align 8 259 Instruction *&CI = Casts[IncomingVal]; 260 if (!CI) { 261 CI = CastInst::CreateBitOrPointerCast(IncomingVal, IntToPtr->getType(), 262 IncomingVal->getName() + ".ptr"); 263 if (auto *IncomingI = dyn_cast<Instruction>(IncomingVal)) { 264 BasicBlock::iterator InsertPos(IncomingI); 265 InsertPos++; 266 if (isa<PHINode>(IncomingI)) 267 InsertPos = IncomingI->getParent()->getFirstInsertionPt(); 268 InsertNewInstBefore(CI, *InsertPos); 269 } else { 270 auto *InsertBB = &IncomingBB->getParent()->getEntryBlock(); 271 InsertNewInstBefore(CI, *InsertBB->getFirstInsertionPt()); 272 } 273 } 274 NewPtrPHI->addIncoming(CI, IncomingBB); 275 } 276 277 // The PtrToCast + IntToPtr will be simplified later 278 return CastInst::CreateBitOrPointerCast(NewPtrPHI, 279 IntToPtr->getOperand(0)->getType()); 280 } 281 282 /// If we have something like phi [add (a,b), add(a,c)] and if a/b/c and the 283 /// adds all have a single use, turn this into a phi and a single binop. 284 Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) { 285 Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 286 assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)); 287 unsigned Opc = FirstInst->getOpcode(); 288 Value *LHSVal = FirstInst->getOperand(0); 289 Value *RHSVal = FirstInst->getOperand(1); 290 291 Type *LHSType = LHSVal->getType(); 292 Type *RHSType = RHSVal->getType(); 293 294 // Scan to see if all operands are the same opcode, and all have one use. 295 for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 296 Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); 297 if (!I || I->getOpcode() != Opc || !I->hasOneUse() || 298 // Verify type of the LHS matches so we don't fold cmp's of different 299 // types. 300 I->getOperand(0)->getType() != LHSType || 301 I->getOperand(1)->getType() != RHSType) 302 return nullptr; 303 304 // If they are CmpInst instructions, check their predicates 305 if (CmpInst *CI = dyn_cast<CmpInst>(I)) 306 if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate()) 307 return nullptr; 308 309 // Keep track of which operand needs a phi node. 310 if (I->getOperand(0) != LHSVal) LHSVal = nullptr; 311 if (I->getOperand(1) != RHSVal) RHSVal = nullptr; 312 } 313 314 // If both LHS and RHS would need a PHI, don't do this transformation, 315 // because it would increase the number of PHIs entering the block, 316 // which leads to higher register pressure. This is especially 317 // bad when the PHIs are in the header of a loop. 318 if (!LHSVal && !RHSVal) 319 return nullptr; 320 321 // Otherwise, this is safe to transform! 322 323 Value *InLHS = FirstInst->getOperand(0); 324 Value *InRHS = FirstInst->getOperand(1); 325 PHINode *NewLHS = nullptr, *NewRHS = nullptr; 326 if (!LHSVal) { 327 NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(), 328 FirstInst->getOperand(0)->getName() + ".pn"); 329 NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); 330 InsertNewInstBefore(NewLHS, PN); 331 LHSVal = NewLHS; 332 } 333 334 if (!RHSVal) { 335 NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(), 336 FirstInst->getOperand(1)->getName() + ".pn"); 337 NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0)); 338 InsertNewInstBefore(NewRHS, PN); 339 RHSVal = NewRHS; 340 } 341 342 // Add all operands to the new PHIs. 343 if (NewLHS || NewRHS) { 344 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 345 Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i)); 346 if (NewLHS) { 347 Value *NewInLHS = InInst->getOperand(0); 348 NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i)); 349 } 350 if (NewRHS) { 351 Value *NewInRHS = InInst->getOperand(1); 352 NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i)); 353 } 354 } 355 } 356 357 if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) { 358 CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 359 LHSVal, RHSVal); 360 PHIArgMergedDebugLoc(NewCI, PN); 361 return NewCI; 362 } 363 364 BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst); 365 BinaryOperator *NewBinOp = 366 BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); 367 368 NewBinOp->copyIRFlags(PN.getIncomingValue(0)); 369 370 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) 371 NewBinOp->andIRFlags(PN.getIncomingValue(i)); 372 373 PHIArgMergedDebugLoc(NewBinOp, PN); 374 return NewBinOp; 375 } 376 377 Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) { 378 GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0)); 379 380 SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(), 381 FirstInst->op_end()); 382 // This is true if all GEP bases are allocas and if all indices into them are 383 // constants. 384 bool AllBasePointersAreAllocas = true; 385 386 // We don't want to replace this phi if the replacement would require 387 // more than one phi, which leads to higher register pressure. This is 388 // especially bad when the PHIs are in the header of a loop. 389 bool NeededPhi = false; 390 391 bool AllInBounds = true; 392 393 // Scan to see if all operands are the same opcode, and all have one use. 394 for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 395 GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i)); 396 if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() || 397 GEP->getNumOperands() != FirstInst->getNumOperands()) 398 return nullptr; 399 400 AllInBounds &= GEP->isInBounds(); 401 402 // Keep track of whether or not all GEPs are of alloca pointers. 403 if (AllBasePointersAreAllocas && 404 (!isa<AllocaInst>(GEP->getOperand(0)) || 405 !GEP->hasAllConstantIndices())) 406 AllBasePointersAreAllocas = false; 407 408 // Compare the operand lists. 409 for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) { 410 if (FirstInst->getOperand(op) == GEP->getOperand(op)) 411 continue; 412 413 // Don't merge two GEPs when two operands differ (introducing phi nodes) 414 // if one of the PHIs has a constant for the index. The index may be 415 // substantially cheaper to compute for the constants, so making it a 416 // variable index could pessimize the path. This also handles the case 417 // for struct indices, which must always be constant. 418 if (isa<ConstantInt>(FirstInst->getOperand(op)) || 419 isa<ConstantInt>(GEP->getOperand(op))) 420 return nullptr; 421 422 if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType()) 423 return nullptr; 424 425 // If we already needed a PHI for an earlier operand, and another operand 426 // also requires a PHI, we'd be introducing more PHIs than we're 427 // eliminating, which increases register pressure on entry to the PHI's 428 // block. 429 if (NeededPhi) 430 return nullptr; 431 432 FixedOperands[op] = nullptr; // Needs a PHI. 433 NeededPhi = true; 434 } 435 } 436 437 // If all of the base pointers of the PHI'd GEPs are from allocas, don't 438 // bother doing this transformation. At best, this will just save a bit of 439 // offset calculation, but all the predecessors will have to materialize the 440 // stack address into a register anyway. We'd actually rather *clone* the 441 // load up into the predecessors so that we have a load of a gep of an alloca, 442 // which can usually all be folded into the load. 443 if (AllBasePointersAreAllocas) 444 return nullptr; 445 446 // Otherwise, this is safe to transform. Insert PHI nodes for each operand 447 // that is variable. 448 SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size()); 449 450 bool HasAnyPHIs = false; 451 for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) { 452 if (FixedOperands[i]) continue; // operand doesn't need a phi. 453 Value *FirstOp = FirstInst->getOperand(i); 454 PHINode *NewPN = PHINode::Create(FirstOp->getType(), e, 455 FirstOp->getName()+".pn"); 456 InsertNewInstBefore(NewPN, PN); 457 458 NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0)); 459 OperandPhis[i] = NewPN; 460 FixedOperands[i] = NewPN; 461 HasAnyPHIs = true; 462 } 463 464 465 // Add all operands to the new PHIs. 466 if (HasAnyPHIs) { 467 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 468 GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i)); 469 BasicBlock *InBB = PN.getIncomingBlock(i); 470 471 for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op) 472 if (PHINode *OpPhi = OperandPhis[op]) 473 OpPhi->addIncoming(InGEP->getOperand(op), InBB); 474 } 475 } 476 477 Value *Base = FixedOperands[0]; 478 GetElementPtrInst *NewGEP = 479 GetElementPtrInst::Create(FirstInst->getSourceElementType(), Base, 480 makeArrayRef(FixedOperands).slice(1)); 481 if (AllInBounds) NewGEP->setIsInBounds(); 482 PHIArgMergedDebugLoc(NewGEP, PN); 483 return NewGEP; 484 } 485 486 487 /// Return true if we know that it is safe to sink the load out of the block 488 /// that defines it. This means that it must be obvious the value of the load is 489 /// not changed from the point of the load to the end of the block it is in. 490 /// 491 /// Finally, it is safe, but not profitable, to sink a load targeting a 492 /// non-address-taken alloca. Doing so will cause us to not promote the alloca 493 /// to a register. 494 static bool isSafeAndProfitableToSinkLoad(LoadInst *L) { 495 BasicBlock::iterator BBI = L->getIterator(), E = L->getParent()->end(); 496 497 for (++BBI; BBI != E; ++BBI) 498 if (BBI->mayWriteToMemory()) 499 return false; 500 501 // Check for non-address taken alloca. If not address-taken already, it isn't 502 // profitable to do this xform. 503 if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) { 504 bool isAddressTaken = false; 505 for (User *U : AI->users()) { 506 if (isa<LoadInst>(U)) continue; 507 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 508 // If storing TO the alloca, then the address isn't taken. 509 if (SI->getOperand(1) == AI) continue; 510 } 511 isAddressTaken = true; 512 break; 513 } 514 515 if (!isAddressTaken && AI->isStaticAlloca()) 516 return false; 517 } 518 519 // If this load is a load from a GEP with a constant offset from an alloca, 520 // then we don't want to sink it. In its present form, it will be 521 // load [constant stack offset]. Sinking it will cause us to have to 522 // materialize the stack addresses in each predecessor in a register only to 523 // do a shared load from register in the successor. 524 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0))) 525 if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0))) 526 if (AI->isStaticAlloca() && GEP->hasAllConstantIndices()) 527 return false; 528 529 return true; 530 } 531 532 Instruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) { 533 LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0)); 534 535 // FIXME: This is overconservative; this transform is allowed in some cases 536 // for atomic operations. 537 if (FirstLI->isAtomic()) 538 return nullptr; 539 540 // When processing loads, we need to propagate two bits of information to the 541 // sunk load: whether it is volatile, and what its alignment is. We currently 542 // don't sink loads when some have their alignment specified and some don't. 543 // visitLoadInst will propagate an alignment onto the load when TD is around, 544 // and if TD isn't around, we can't handle the mixed case. 545 bool isVolatile = FirstLI->isVolatile(); 546 unsigned LoadAlignment = FirstLI->getAlignment(); 547 unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace(); 548 549 // We can't sink the load if the loaded value could be modified between the 550 // load and the PHI. 551 if (FirstLI->getParent() != PN.getIncomingBlock(0) || 552 !isSafeAndProfitableToSinkLoad(FirstLI)) 553 return nullptr; 554 555 // If the PHI is of volatile loads and the load block has multiple 556 // successors, sinking it would remove a load of the volatile value from 557 // the path through the other successor. 558 if (isVolatile && 559 FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1) 560 return nullptr; 561 562 // Check to see if all arguments are the same operation. 563 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 564 LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i)); 565 if (!LI || !LI->hasOneUse()) 566 return nullptr; 567 568 // We can't sink the load if the loaded value could be modified between 569 // the load and the PHI. 570 if (LI->isVolatile() != isVolatile || 571 LI->getParent() != PN.getIncomingBlock(i) || 572 LI->getPointerAddressSpace() != LoadAddrSpace || 573 !isSafeAndProfitableToSinkLoad(LI)) 574 return nullptr; 575 576 // If some of the loads have an alignment specified but not all of them, 577 // we can't do the transformation. 578 if ((LoadAlignment != 0) != (LI->getAlignment() != 0)) 579 return nullptr; 580 581 LoadAlignment = std::min(LoadAlignment, LI->getAlignment()); 582 583 // If the PHI is of volatile loads and the load block has multiple 584 // successors, sinking it would remove a load of the volatile value from 585 // the path through the other successor. 586 if (isVolatile && 587 LI->getParent()->getTerminator()->getNumSuccessors() != 1) 588 return nullptr; 589 } 590 591 // Okay, they are all the same operation. Create a new PHI node of the 592 // correct type, and PHI together all of the LHS's of the instructions. 593 PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(), 594 PN.getNumIncomingValues(), 595 PN.getName()+".in"); 596 597 Value *InVal = FirstLI->getOperand(0); 598 NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 599 LoadInst *NewLI = new LoadInst(NewPN, "", isVolatile, LoadAlignment); 600 601 unsigned KnownIDs[] = { 602 LLVMContext::MD_tbaa, 603 LLVMContext::MD_range, 604 LLVMContext::MD_invariant_load, 605 LLVMContext::MD_alias_scope, 606 LLVMContext::MD_noalias, 607 LLVMContext::MD_nonnull, 608 LLVMContext::MD_align, 609 LLVMContext::MD_dereferenceable, 610 LLVMContext::MD_dereferenceable_or_null, 611 }; 612 613 for (unsigned ID : KnownIDs) 614 NewLI->setMetadata(ID, FirstLI->getMetadata(ID)); 615 616 // Add all operands to the new PHI and combine TBAA metadata. 617 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 618 LoadInst *LI = cast<LoadInst>(PN.getIncomingValue(i)); 619 combineMetadata(NewLI, LI, KnownIDs); 620 Value *NewInVal = LI->getOperand(0); 621 if (NewInVal != InVal) 622 InVal = nullptr; 623 NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 624 } 625 626 if (InVal) { 627 // The new PHI unions all of the same values together. This is really 628 // common, so we handle it intelligently here for compile-time speed. 629 NewLI->setOperand(0, InVal); 630 delete NewPN; 631 } else { 632 InsertNewInstBefore(NewPN, PN); 633 } 634 635 // If this was a volatile load that we are merging, make sure to loop through 636 // and mark all the input loads as non-volatile. If we don't do this, we will 637 // insert a new volatile load and the old ones will not be deletable. 638 if (isVolatile) 639 for (Value *IncValue : PN.incoming_values()) 640 cast<LoadInst>(IncValue)->setVolatile(false); 641 642 PHIArgMergedDebugLoc(NewLI, PN); 643 return NewLI; 644 } 645 646 /// TODO: This function could handle other cast types, but then it might 647 /// require special-casing a cast from the 'i1' type. See the comment in 648 /// FoldPHIArgOpIntoPHI() about pessimizing illegal integer types. 649 Instruction *InstCombiner::FoldPHIArgZextsIntoPHI(PHINode &Phi) { 650 // We cannot create a new instruction after the PHI if the terminator is an 651 // EHPad because there is no valid insertion point. 652 if (TerminatorInst *TI = Phi.getParent()->getTerminator()) 653 if (TI->isEHPad()) 654 return nullptr; 655 656 // Early exit for the common case of a phi with two operands. These are 657 // handled elsewhere. See the comment below where we check the count of zexts 658 // and constants for more details. 659 unsigned NumIncomingValues = Phi.getNumIncomingValues(); 660 if (NumIncomingValues < 3) 661 return nullptr; 662 663 // Find the narrower type specified by the first zext. 664 Type *NarrowType = nullptr; 665 for (Value *V : Phi.incoming_values()) { 666 if (auto *Zext = dyn_cast<ZExtInst>(V)) { 667 NarrowType = Zext->getSrcTy(); 668 break; 669 } 670 } 671 if (!NarrowType) 672 return nullptr; 673 674 // Walk the phi operands checking that we only have zexts or constants that 675 // we can shrink for free. Store the new operands for the new phi. 676 SmallVector<Value *, 4> NewIncoming; 677 unsigned NumZexts = 0; 678 unsigned NumConsts = 0; 679 for (Value *V : Phi.incoming_values()) { 680 if (auto *Zext = dyn_cast<ZExtInst>(V)) { 681 // All zexts must be identical and have one use. 682 if (Zext->getSrcTy() != NarrowType || !Zext->hasOneUse()) 683 return nullptr; 684 NewIncoming.push_back(Zext->getOperand(0)); 685 NumZexts++; 686 } else if (auto *C = dyn_cast<Constant>(V)) { 687 // Make sure that constants can fit in the new type. 688 Constant *Trunc = ConstantExpr::getTrunc(C, NarrowType); 689 if (ConstantExpr::getZExt(Trunc, C->getType()) != C) 690 return nullptr; 691 NewIncoming.push_back(Trunc); 692 NumConsts++; 693 } else { 694 // If it's not a cast or a constant, bail out. 695 return nullptr; 696 } 697 } 698 699 // The more common cases of a phi with no constant operands or just one 700 // variable operand are handled by FoldPHIArgOpIntoPHI() and foldOpIntoPhi() 701 // respectively. foldOpIntoPhi() wants to do the opposite transform that is 702 // performed here. It tries to replicate a cast in the phi operand's basic 703 // block to expose other folding opportunities. Thus, InstCombine will 704 // infinite loop without this check. 705 if (NumConsts == 0 || NumZexts < 2) 706 return nullptr; 707 708 // All incoming values are zexts or constants that are safe to truncate. 709 // Create a new phi node of the narrow type, phi together all of the new 710 // operands, and zext the result back to the original type. 711 PHINode *NewPhi = PHINode::Create(NarrowType, NumIncomingValues, 712 Phi.getName() + ".shrunk"); 713 for (unsigned i = 0; i != NumIncomingValues; ++i) 714 NewPhi->addIncoming(NewIncoming[i], Phi.getIncomingBlock(i)); 715 716 InsertNewInstBefore(NewPhi, Phi); 717 return CastInst::CreateZExtOrBitCast(NewPhi, Phi.getType()); 718 } 719 720 /// If all operands to a PHI node are the same "unary" operator and they all are 721 /// only used by the PHI, PHI together their inputs, and do the operation once, 722 /// to the result of the PHI. 723 Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) { 724 // We cannot create a new instruction after the PHI if the terminator is an 725 // EHPad because there is no valid insertion point. 726 if (TerminatorInst *TI = PN.getParent()->getTerminator()) 727 if (TI->isEHPad()) 728 return nullptr; 729 730 Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 731 732 if (isa<GetElementPtrInst>(FirstInst)) 733 return FoldPHIArgGEPIntoPHI(PN); 734 if (isa<LoadInst>(FirstInst)) 735 return FoldPHIArgLoadIntoPHI(PN); 736 737 // Scan the instruction, looking for input operations that can be folded away. 738 // If all input operands to the phi are the same instruction (e.g. a cast from 739 // the same type or "+42") we can pull the operation through the PHI, reducing 740 // code size and simplifying code. 741 Constant *ConstantOp = nullptr; 742 Type *CastSrcTy = nullptr; 743 744 if (isa<CastInst>(FirstInst)) { 745 CastSrcTy = FirstInst->getOperand(0)->getType(); 746 747 // Be careful about transforming integer PHIs. We don't want to pessimize 748 // the code by turning an i32 into an i1293. 749 if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) { 750 if (!shouldChangeType(PN.getType(), CastSrcTy)) 751 return nullptr; 752 } 753 } else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) { 754 // Can fold binop, compare or shift here if the RHS is a constant, 755 // otherwise call FoldPHIArgBinOpIntoPHI. 756 ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1)); 757 if (!ConstantOp) 758 return FoldPHIArgBinOpIntoPHI(PN); 759 } else { 760 return nullptr; // Cannot fold this operation. 761 } 762 763 // Check to see if all arguments are the same operation. 764 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 765 Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); 766 if (!I || !I->hasOneUse() || !I->isSameOperationAs(FirstInst)) 767 return nullptr; 768 if (CastSrcTy) { 769 if (I->getOperand(0)->getType() != CastSrcTy) 770 return nullptr; // Cast operation must match. 771 } else if (I->getOperand(1) != ConstantOp) { 772 return nullptr; 773 } 774 } 775 776 // Okay, they are all the same operation. Create a new PHI node of the 777 // correct type, and PHI together all of the LHS's of the instructions. 778 PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(), 779 PN.getNumIncomingValues(), 780 PN.getName()+".in"); 781 782 Value *InVal = FirstInst->getOperand(0); 783 NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 784 785 // Add all operands to the new PHI. 786 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 787 Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0); 788 if (NewInVal != InVal) 789 InVal = nullptr; 790 NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 791 } 792 793 Value *PhiVal; 794 if (InVal) { 795 // The new PHI unions all of the same values together. This is really 796 // common, so we handle it intelligently here for compile-time speed. 797 PhiVal = InVal; 798 delete NewPN; 799 } else { 800 InsertNewInstBefore(NewPN, PN); 801 PhiVal = NewPN; 802 } 803 804 // Insert and return the new operation. 805 if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) { 806 CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal, 807 PN.getType()); 808 PHIArgMergedDebugLoc(NewCI, PN); 809 return NewCI; 810 } 811 812 if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) { 813 BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); 814 BinOp->copyIRFlags(PN.getIncomingValue(0)); 815 816 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) 817 BinOp->andIRFlags(PN.getIncomingValue(i)); 818 819 PHIArgMergedDebugLoc(BinOp, PN); 820 return BinOp; 821 } 822 823 CmpInst *CIOp = cast<CmpInst>(FirstInst); 824 CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 825 PhiVal, ConstantOp); 826 PHIArgMergedDebugLoc(NewCI, PN); 827 return NewCI; 828 } 829 830 /// Return true if this PHI node is only used by a PHI node cycle that is dead. 831 static bool DeadPHICycle(PHINode *PN, 832 SmallPtrSetImpl<PHINode*> &PotentiallyDeadPHIs) { 833 if (PN->use_empty()) return true; 834 if (!PN->hasOneUse()) return false; 835 836 // Remember this node, and if we find the cycle, return. 837 if (!PotentiallyDeadPHIs.insert(PN).second) 838 return true; 839 840 // Don't scan crazily complex things. 841 if (PotentiallyDeadPHIs.size() == 16) 842 return false; 843 844 if (PHINode *PU = dyn_cast<PHINode>(PN->user_back())) 845 return DeadPHICycle(PU, PotentiallyDeadPHIs); 846 847 return false; 848 } 849 850 /// Return true if this phi node is always equal to NonPhiInVal. 851 /// This happens with mutually cyclic phi nodes like: 852 /// z = some value; x = phi (y, z); y = phi (x, z) 853 static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal, 854 SmallPtrSetImpl<PHINode*> &ValueEqualPHIs) { 855 // See if we already saw this PHI node. 856 if (!ValueEqualPHIs.insert(PN).second) 857 return true; 858 859 // Don't scan crazily complex things. 860 if (ValueEqualPHIs.size() == 16) 861 return false; 862 863 // Scan the operands to see if they are either phi nodes or are equal to 864 // the value. 865 for (Value *Op : PN->incoming_values()) { 866 if (PHINode *OpPN = dyn_cast<PHINode>(Op)) { 867 if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs)) 868 return false; 869 } else if (Op != NonPhiInVal) 870 return false; 871 } 872 873 return true; 874 } 875 876 /// Return an existing non-zero constant if this phi node has one, otherwise 877 /// return constant 1. 878 static ConstantInt *GetAnyNonZeroConstInt(PHINode &PN) { 879 assert(isa<IntegerType>(PN.getType()) && "Expect only integer type phi"); 880 for (Value *V : PN.operands()) 881 if (auto *ConstVA = dyn_cast<ConstantInt>(V)) 882 if (!ConstVA->isZero()) 883 return ConstVA; 884 return ConstantInt::get(cast<IntegerType>(PN.getType()), 1); 885 } 886 887 namespace { 888 struct PHIUsageRecord { 889 unsigned PHIId; // The ID # of the PHI (something determinstic to sort on) 890 unsigned Shift; // The amount shifted. 891 Instruction *Inst; // The trunc instruction. 892 893 PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User) 894 : PHIId(pn), Shift(Sh), Inst(User) {} 895 896 bool operator<(const PHIUsageRecord &RHS) const { 897 if (PHIId < RHS.PHIId) return true; 898 if (PHIId > RHS.PHIId) return false; 899 if (Shift < RHS.Shift) return true; 900 if (Shift > RHS.Shift) return false; 901 return Inst->getType()->getPrimitiveSizeInBits() < 902 RHS.Inst->getType()->getPrimitiveSizeInBits(); 903 } 904 }; 905 906 struct LoweredPHIRecord { 907 PHINode *PN; // The PHI that was lowered. 908 unsigned Shift; // The amount shifted. 909 unsigned Width; // The width extracted. 910 911 LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty) 912 : PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {} 913 914 // Ctor form used by DenseMap. 915 LoweredPHIRecord(PHINode *pn, unsigned Sh) 916 : PN(pn), Shift(Sh), Width(0) {} 917 }; 918 } 919 920 namespace llvm { 921 template<> 922 struct DenseMapInfo<LoweredPHIRecord> { 923 static inline LoweredPHIRecord getEmptyKey() { 924 return LoweredPHIRecord(nullptr, 0); 925 } 926 static inline LoweredPHIRecord getTombstoneKey() { 927 return LoweredPHIRecord(nullptr, 1); 928 } 929 static unsigned getHashValue(const LoweredPHIRecord &Val) { 930 return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^ 931 (Val.Width>>3); 932 } 933 static bool isEqual(const LoweredPHIRecord &LHS, 934 const LoweredPHIRecord &RHS) { 935 return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift && 936 LHS.Width == RHS.Width; 937 } 938 }; 939 } 940 941 942 /// This is an integer PHI and we know that it has an illegal type: see if it is 943 /// only used by trunc or trunc(lshr) operations. If so, we split the PHI into 944 /// the various pieces being extracted. This sort of thing is introduced when 945 /// SROA promotes an aggregate to large integer values. 946 /// 947 /// TODO: The user of the trunc may be an bitcast to float/double/vector or an 948 /// inttoptr. We should produce new PHIs in the right type. 949 /// 950 Instruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) { 951 // PHIUsers - Keep track of all of the truncated values extracted from a set 952 // of PHIs, along with their offset. These are the things we want to rewrite. 953 SmallVector<PHIUsageRecord, 16> PHIUsers; 954 955 // PHIs are often mutually cyclic, so we keep track of a whole set of PHI 956 // nodes which are extracted from. PHIsToSlice is a set we use to avoid 957 // revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to 958 // check the uses of (to ensure they are all extracts). 959 SmallVector<PHINode*, 8> PHIsToSlice; 960 SmallPtrSet<PHINode*, 8> PHIsInspected; 961 962 PHIsToSlice.push_back(&FirstPhi); 963 PHIsInspected.insert(&FirstPhi); 964 965 for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) { 966 PHINode *PN = PHIsToSlice[PHIId]; 967 968 // Scan the input list of the PHI. If any input is an invoke, and if the 969 // input is defined in the predecessor, then we won't be split the critical 970 // edge which is required to insert a truncate. Because of this, we have to 971 // bail out. 972 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 973 InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i)); 974 if (!II) continue; 975 if (II->getParent() != PN->getIncomingBlock(i)) 976 continue; 977 978 // If we have a phi, and if it's directly in the predecessor, then we have 979 // a critical edge where we need to put the truncate. Since we can't 980 // split the edge in instcombine, we have to bail out. 981 return nullptr; 982 } 983 984 for (User *U : PN->users()) { 985 Instruction *UserI = cast<Instruction>(U); 986 987 // If the user is a PHI, inspect its uses recursively. 988 if (PHINode *UserPN = dyn_cast<PHINode>(UserI)) { 989 if (PHIsInspected.insert(UserPN).second) 990 PHIsToSlice.push_back(UserPN); 991 continue; 992 } 993 994 // Truncates are always ok. 995 if (isa<TruncInst>(UserI)) { 996 PHIUsers.push_back(PHIUsageRecord(PHIId, 0, UserI)); 997 continue; 998 } 999 1000 // Otherwise it must be a lshr which can only be used by one trunc. 1001 if (UserI->getOpcode() != Instruction::LShr || 1002 !UserI->hasOneUse() || !isa<TruncInst>(UserI->user_back()) || 1003 !isa<ConstantInt>(UserI->getOperand(1))) 1004 return nullptr; 1005 1006 unsigned Shift = cast<ConstantInt>(UserI->getOperand(1))->getZExtValue(); 1007 PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, UserI->user_back())); 1008 } 1009 } 1010 1011 // If we have no users, they must be all self uses, just nuke the PHI. 1012 if (PHIUsers.empty()) 1013 return replaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType())); 1014 1015 // If this phi node is transformable, create new PHIs for all the pieces 1016 // extracted out of it. First, sort the users by their offset and size. 1017 array_pod_sort(PHIUsers.begin(), PHIUsers.end()); 1018 1019 LLVM_DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n'; 1020 for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) dbgs() 1021 << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n';); 1022 1023 // PredValues - This is a temporary used when rewriting PHI nodes. It is 1024 // hoisted out here to avoid construction/destruction thrashing. 1025 DenseMap<BasicBlock*, Value*> PredValues; 1026 1027 // ExtractedVals - Each new PHI we introduce is saved here so we don't 1028 // introduce redundant PHIs. 1029 DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals; 1030 1031 for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) { 1032 unsigned PHIId = PHIUsers[UserI].PHIId; 1033 PHINode *PN = PHIsToSlice[PHIId]; 1034 unsigned Offset = PHIUsers[UserI].Shift; 1035 Type *Ty = PHIUsers[UserI].Inst->getType(); 1036 1037 PHINode *EltPHI; 1038 1039 // If we've already lowered a user like this, reuse the previously lowered 1040 // value. 1041 if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == nullptr) { 1042 1043 // Otherwise, Create the new PHI node for this user. 1044 EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(), 1045 PN->getName()+".off"+Twine(Offset), PN); 1046 assert(EltPHI->getType() != PN->getType() && 1047 "Truncate didn't shrink phi?"); 1048 1049 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1050 BasicBlock *Pred = PN->getIncomingBlock(i); 1051 Value *&PredVal = PredValues[Pred]; 1052 1053 // If we already have a value for this predecessor, reuse it. 1054 if (PredVal) { 1055 EltPHI->addIncoming(PredVal, Pred); 1056 continue; 1057 } 1058 1059 // Handle the PHI self-reuse case. 1060 Value *InVal = PN->getIncomingValue(i); 1061 if (InVal == PN) { 1062 PredVal = EltPHI; 1063 EltPHI->addIncoming(PredVal, Pred); 1064 continue; 1065 } 1066 1067 if (PHINode *InPHI = dyn_cast<PHINode>(PN)) { 1068 // If the incoming value was a PHI, and if it was one of the PHIs we 1069 // already rewrote it, just use the lowered value. 1070 if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) { 1071 PredVal = Res; 1072 EltPHI->addIncoming(PredVal, Pred); 1073 continue; 1074 } 1075 } 1076 1077 // Otherwise, do an extract in the predecessor. 1078 Builder.SetInsertPoint(Pred->getTerminator()); 1079 Value *Res = InVal; 1080 if (Offset) 1081 Res = Builder.CreateLShr(Res, ConstantInt::get(InVal->getType(), 1082 Offset), "extract"); 1083 Res = Builder.CreateTrunc(Res, Ty, "extract.t"); 1084 PredVal = Res; 1085 EltPHI->addIncoming(Res, Pred); 1086 1087 // If the incoming value was a PHI, and if it was one of the PHIs we are 1088 // rewriting, we will ultimately delete the code we inserted. This 1089 // means we need to revisit that PHI to make sure we extract out the 1090 // needed piece. 1091 if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i))) 1092 if (PHIsInspected.count(OldInVal)) { 1093 unsigned RefPHIId = 1094 find(PHIsToSlice, OldInVal) - PHIsToSlice.begin(); 1095 PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset, 1096 cast<Instruction>(Res))); 1097 ++UserE; 1098 } 1099 } 1100 PredValues.clear(); 1101 1102 LLVM_DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": " 1103 << *EltPHI << '\n'); 1104 ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI; 1105 } 1106 1107 // Replace the use of this piece with the PHI node. 1108 replaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI); 1109 } 1110 1111 // Replace all the remaining uses of the PHI nodes (self uses and the lshrs) 1112 // with undefs. 1113 Value *Undef = UndefValue::get(FirstPhi.getType()); 1114 for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) 1115 replaceInstUsesWith(*PHIsToSlice[i], Undef); 1116 return replaceInstUsesWith(FirstPhi, Undef); 1117 } 1118 1119 // PHINode simplification 1120 // 1121 Instruction *InstCombiner::visitPHINode(PHINode &PN) { 1122 if (Value *V = SimplifyInstruction(&PN, SQ.getWithInstruction(&PN))) 1123 return replaceInstUsesWith(PN, V); 1124 1125 if (Instruction *Result = FoldPHIArgZextsIntoPHI(PN)) 1126 return Result; 1127 1128 // If all PHI operands are the same operation, pull them through the PHI, 1129 // reducing code size. 1130 if (isa<Instruction>(PN.getIncomingValue(0)) && 1131 isa<Instruction>(PN.getIncomingValue(1)) && 1132 cast<Instruction>(PN.getIncomingValue(0))->getOpcode() == 1133 cast<Instruction>(PN.getIncomingValue(1))->getOpcode() && 1134 // FIXME: The hasOneUse check will fail for PHIs that use the value more 1135 // than themselves more than once. 1136 PN.getIncomingValue(0)->hasOneUse()) 1137 if (Instruction *Result = FoldPHIArgOpIntoPHI(PN)) 1138 return Result; 1139 1140 // If this is a trivial cycle in the PHI node graph, remove it. Basically, if 1141 // this PHI only has a single use (a PHI), and if that PHI only has one use (a 1142 // PHI)... break the cycle. 1143 if (PN.hasOneUse()) { 1144 if (Instruction *Result = FoldIntegerTypedPHI(PN)) 1145 return Result; 1146 1147 Instruction *PHIUser = cast<Instruction>(PN.user_back()); 1148 if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) { 1149 SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs; 1150 PotentiallyDeadPHIs.insert(&PN); 1151 if (DeadPHICycle(PU, PotentiallyDeadPHIs)) 1152 return replaceInstUsesWith(PN, UndefValue::get(PN.getType())); 1153 } 1154 1155 // If this phi has a single use, and if that use just computes a value for 1156 // the next iteration of a loop, delete the phi. This occurs with unused 1157 // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this 1158 // common case here is good because the only other things that catch this 1159 // are induction variable analysis (sometimes) and ADCE, which is only run 1160 // late. 1161 if (PHIUser->hasOneUse() && 1162 (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) && 1163 PHIUser->user_back() == &PN) { 1164 return replaceInstUsesWith(PN, UndefValue::get(PN.getType())); 1165 } 1166 // When a PHI is used only to be compared with zero, it is safe to replace 1167 // an incoming value proved as known nonzero with any non-zero constant. 1168 // For example, in the code below, the incoming value %v can be replaced 1169 // with any non-zero constant based on the fact that the PHI is only used to 1170 // be compared with zero and %v is a known non-zero value: 1171 // %v = select %cond, 1, 2 1172 // %p = phi [%v, BB] ... 1173 // icmp eq, %p, 0 1174 auto *CmpInst = dyn_cast<ICmpInst>(PHIUser); 1175 // FIXME: To be simple, handle only integer type for now. 1176 if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() && 1177 match(CmpInst->getOperand(1), m_Zero())) { 1178 ConstantInt *NonZeroConst = nullptr; 1179 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { 1180 Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator(); 1181 Value *VA = PN.getIncomingValue(i); 1182 if (isKnownNonZero(VA, DL, 0, &AC, CtxI, &DT)) { 1183 if (!NonZeroConst) 1184 NonZeroConst = GetAnyNonZeroConstInt(PN); 1185 PN.setIncomingValue(i, NonZeroConst); 1186 } 1187 } 1188 } 1189 } 1190 1191 // We sometimes end up with phi cycles that non-obviously end up being the 1192 // same value, for example: 1193 // z = some value; x = phi (y, z); y = phi (x, z) 1194 // where the phi nodes don't necessarily need to be in the same block. Do a 1195 // quick check to see if the PHI node only contains a single non-phi value, if 1196 // so, scan to see if the phi cycle is actually equal to that value. 1197 { 1198 unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues(); 1199 // Scan for the first non-phi operand. 1200 while (InValNo != NumIncomingVals && 1201 isa<PHINode>(PN.getIncomingValue(InValNo))) 1202 ++InValNo; 1203 1204 if (InValNo != NumIncomingVals) { 1205 Value *NonPhiInVal = PN.getIncomingValue(InValNo); 1206 1207 // Scan the rest of the operands to see if there are any conflicts, if so 1208 // there is no need to recursively scan other phis. 1209 for (++InValNo; InValNo != NumIncomingVals; ++InValNo) { 1210 Value *OpVal = PN.getIncomingValue(InValNo); 1211 if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal)) 1212 break; 1213 } 1214 1215 // If we scanned over all operands, then we have one unique value plus 1216 // phi values. Scan PHI nodes to see if they all merge in each other or 1217 // the value. 1218 if (InValNo == NumIncomingVals) { 1219 SmallPtrSet<PHINode*, 16> ValueEqualPHIs; 1220 if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs)) 1221 return replaceInstUsesWith(PN, NonPhiInVal); 1222 } 1223 } 1224 } 1225 1226 // If there are multiple PHIs, sort their operands so that they all list 1227 // the blocks in the same order. This will help identical PHIs be eliminated 1228 // by other passes. Other passes shouldn't depend on this for correctness 1229 // however. 1230 PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin()); 1231 if (&PN != FirstPN) 1232 for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) { 1233 BasicBlock *BBA = PN.getIncomingBlock(i); 1234 BasicBlock *BBB = FirstPN->getIncomingBlock(i); 1235 if (BBA != BBB) { 1236 Value *VA = PN.getIncomingValue(i); 1237 unsigned j = PN.getBasicBlockIndex(BBB); 1238 Value *VB = PN.getIncomingValue(j); 1239 PN.setIncomingBlock(i, BBB); 1240 PN.setIncomingValue(i, VB); 1241 PN.setIncomingBlock(j, BBA); 1242 PN.setIncomingValue(j, VA); 1243 // NOTE: Instcombine normally would want us to "return &PN" if we 1244 // modified any of the operands of an instruction. However, since we 1245 // aren't adding or removing uses (just rearranging them) we don't do 1246 // this in this case. 1247 } 1248 } 1249 1250 // If this is an integer PHI and we know that it has an illegal type, see if 1251 // it is only used by trunc or trunc(lshr) operations. If so, we split the 1252 // PHI into the various pieces being extracted. This sort of thing is 1253 // introduced when SROA promotes an aggregate to a single large integer type. 1254 if (PN.getType()->isIntegerTy() && 1255 !DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) 1256 if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) 1257 return Res; 1258 1259 return nullptr; 1260 } 1261