1 //===-- Analysis.cpp - CodeGen LLVM IR Analysis Utilities -----------------===// 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 defines several CodeGen-specific LLVM IR analysis utilities. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/CodeGen/Analysis.h" 14 #include "llvm/Analysis/ValueTracking.h" 15 #include "llvm/CodeGen/MachineFunction.h" 16 #include "llvm/CodeGen/TargetInstrInfo.h" 17 #include "llvm/CodeGen/TargetLowering.h" 18 #include "llvm/CodeGen/TargetSubtargetInfo.h" 19 #include "llvm/IR/DataLayout.h" 20 #include "llvm/IR/DerivedTypes.h" 21 #include "llvm/IR/Function.h" 22 #include "llvm/IR/Instructions.h" 23 #include "llvm/IR/IntrinsicInst.h" 24 #include "llvm/IR/Module.h" 25 #include "llvm/Support/ErrorHandling.h" 26 #include "llvm/Target/TargetMachine.h" 27 28 using namespace llvm; 29 30 /// Compute the linearized index of a member in a nested aggregate/struct/array 31 /// by recursing and accumulating CurIndex as long as there are indices in the 32 /// index list. 33 unsigned llvm::ComputeLinearIndex(Type *Ty, 34 const unsigned *Indices, 35 const unsigned *IndicesEnd, 36 unsigned CurIndex) { 37 // Base case: We're done. 38 if (Indices && Indices == IndicesEnd) 39 return CurIndex; 40 41 // Given a struct type, recursively traverse the elements. 42 if (StructType *STy = dyn_cast<StructType>(Ty)) { 43 for (auto I : llvm::enumerate(STy->elements())) { 44 Type *ET = I.value(); 45 if (Indices && *Indices == I.index()) 46 return ComputeLinearIndex(ET, Indices + 1, IndicesEnd, CurIndex); 47 CurIndex = ComputeLinearIndex(ET, nullptr, nullptr, CurIndex); 48 } 49 assert(!Indices && "Unexpected out of bound"); 50 return CurIndex; 51 } 52 // Given an array type, recursively traverse the elements. 53 else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 54 Type *EltTy = ATy->getElementType(); 55 unsigned NumElts = ATy->getNumElements(); 56 // Compute the Linear offset when jumping one element of the array 57 unsigned EltLinearOffset = ComputeLinearIndex(EltTy, nullptr, nullptr, 0); 58 if (Indices) { 59 assert(*Indices < NumElts && "Unexpected out of bound"); 60 // If the indice is inside the array, compute the index to the requested 61 // elt and recurse inside the element with the end of the indices list 62 CurIndex += EltLinearOffset* *Indices; 63 return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex); 64 } 65 CurIndex += EltLinearOffset*NumElts; 66 return CurIndex; 67 } 68 // We haven't found the type we're looking for, so keep searching. 69 return CurIndex + 1; 70 } 71 72 /// ComputeValueVTs - Given an LLVM IR type, compute a sequence of 73 /// EVTs that represent all the individual underlying 74 /// non-aggregate types that comprise it. 75 /// 76 /// If Offsets is non-null, it points to a vector to be filled in 77 /// with the in-memory offsets of each of the individual values. 78 /// 79 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL, 80 Type *Ty, SmallVectorImpl<EVT> &ValueVTs, 81 SmallVectorImpl<EVT> *MemVTs, 82 SmallVectorImpl<TypeSize> *Offsets, 83 TypeSize StartingOffset) { 84 assert((Ty->isScalableTy() == StartingOffset.isScalable() || 85 StartingOffset.isZero()) && 86 "Offset/TypeSize mismatch!"); 87 // Given a struct type, recursively traverse the elements. 88 if (StructType *STy = dyn_cast<StructType>(Ty)) { 89 // If the Offsets aren't needed, don't query the struct layout. This allows 90 // us to support structs with scalable vectors for operations that don't 91 // need offsets. 92 const StructLayout *SL = Offsets ? DL.getStructLayout(STy) : nullptr; 93 for (StructType::element_iterator EB = STy->element_begin(), 94 EI = EB, 95 EE = STy->element_end(); 96 EI != EE; ++EI) { 97 // Don't compute the element offset if we didn't get a StructLayout above. 98 TypeSize EltOffset = 99 SL ? SL->getElementOffset(EI - EB) : TypeSize::getZero(); 100 ComputeValueVTs(TLI, DL, *EI, ValueVTs, MemVTs, Offsets, 101 StartingOffset + EltOffset); 102 } 103 return; 104 } 105 // Given an array type, recursively traverse the elements. 106 if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 107 Type *EltTy = ATy->getElementType(); 108 TypeSize EltSize = DL.getTypeAllocSize(EltTy); 109 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i) 110 ComputeValueVTs(TLI, DL, EltTy, ValueVTs, MemVTs, Offsets, 111 StartingOffset + i * EltSize); 112 return; 113 } 114 // Interpret void as zero return values. 115 if (Ty->isVoidTy()) 116 return; 117 // Base case: we can get an EVT for this LLVM IR type. 118 ValueVTs.push_back(TLI.getValueType(DL, Ty)); 119 if (MemVTs) 120 MemVTs->push_back(TLI.getMemValueType(DL, Ty)); 121 if (Offsets) 122 Offsets->push_back(StartingOffset); 123 } 124 125 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL, 126 Type *Ty, SmallVectorImpl<EVT> &ValueVTs, 127 SmallVectorImpl<EVT> *MemVTs, 128 SmallVectorImpl<uint64_t> *FixedOffsets, 129 uint64_t StartingOffset) { 130 TypeSize Offset = TypeSize::getFixed(StartingOffset); 131 if (FixedOffsets) { 132 SmallVector<TypeSize, 4> Offsets; 133 ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, &Offsets, Offset); 134 for (TypeSize Offset : Offsets) 135 FixedOffsets->push_back(Offset.getFixedValue()); 136 } else { 137 ComputeValueVTs(TLI, DL, Ty, ValueVTs, MemVTs, nullptr, Offset); 138 } 139 } 140 141 void llvm::computeValueLLTs(const DataLayout &DL, Type &Ty, 142 SmallVectorImpl<LLT> &ValueTys, 143 SmallVectorImpl<uint64_t> *Offsets, 144 uint64_t StartingOffset) { 145 // Given a struct type, recursively traverse the elements. 146 if (StructType *STy = dyn_cast<StructType>(&Ty)) { 147 // If the Offsets aren't needed, don't query the struct layout. This allows 148 // us to support structs with scalable vectors for operations that don't 149 // need offsets. 150 const StructLayout *SL = Offsets ? DL.getStructLayout(STy) : nullptr; 151 for (unsigned I = 0, E = STy->getNumElements(); I != E; ++I) { 152 uint64_t EltOffset = SL ? SL->getElementOffset(I) : 0; 153 computeValueLLTs(DL, *STy->getElementType(I), ValueTys, Offsets, 154 StartingOffset + EltOffset); 155 } 156 return; 157 } 158 // Given an array type, recursively traverse the elements. 159 if (ArrayType *ATy = dyn_cast<ArrayType>(&Ty)) { 160 Type *EltTy = ATy->getElementType(); 161 uint64_t EltSize = DL.getTypeAllocSize(EltTy).getFixedValue(); 162 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i) 163 computeValueLLTs(DL, *EltTy, ValueTys, Offsets, 164 StartingOffset + i * EltSize); 165 return; 166 } 167 // Interpret void as zero return values. 168 if (Ty.isVoidTy()) 169 return; 170 // Base case: we can get an LLT for this LLVM IR type. 171 ValueTys.push_back(getLLTForType(Ty, DL)); 172 if (Offsets != nullptr) 173 Offsets->push_back(StartingOffset * 8); 174 } 175 176 /// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V. 177 GlobalValue *llvm::ExtractTypeInfo(Value *V) { 178 V = V->stripPointerCasts(); 179 GlobalValue *GV = dyn_cast<GlobalValue>(V); 180 GlobalVariable *Var = dyn_cast<GlobalVariable>(V); 181 182 if (Var && Var->getName() == "llvm.eh.catch.all.value") { 183 assert(Var->hasInitializer() && 184 "The EH catch-all value must have an initializer"); 185 Value *Init = Var->getInitializer(); 186 GV = dyn_cast<GlobalValue>(Init); 187 if (!GV) V = cast<ConstantPointerNull>(Init); 188 } 189 190 assert((GV || isa<ConstantPointerNull>(V)) && 191 "TypeInfo must be a global variable or NULL"); 192 return GV; 193 } 194 195 /// getFCmpCondCode - Return the ISD condition code corresponding to 196 /// the given LLVM IR floating-point condition code. This includes 197 /// consideration of global floating-point math flags. 198 /// 199 ISD::CondCode llvm::getFCmpCondCode(FCmpInst::Predicate Pred) { 200 switch (Pred) { 201 case FCmpInst::FCMP_FALSE: return ISD::SETFALSE; 202 case FCmpInst::FCMP_OEQ: return ISD::SETOEQ; 203 case FCmpInst::FCMP_OGT: return ISD::SETOGT; 204 case FCmpInst::FCMP_OGE: return ISD::SETOGE; 205 case FCmpInst::FCMP_OLT: return ISD::SETOLT; 206 case FCmpInst::FCMP_OLE: return ISD::SETOLE; 207 case FCmpInst::FCMP_ONE: return ISD::SETONE; 208 case FCmpInst::FCMP_ORD: return ISD::SETO; 209 case FCmpInst::FCMP_UNO: return ISD::SETUO; 210 case FCmpInst::FCMP_UEQ: return ISD::SETUEQ; 211 case FCmpInst::FCMP_UGT: return ISD::SETUGT; 212 case FCmpInst::FCMP_UGE: return ISD::SETUGE; 213 case FCmpInst::FCMP_ULT: return ISD::SETULT; 214 case FCmpInst::FCMP_ULE: return ISD::SETULE; 215 case FCmpInst::FCMP_UNE: return ISD::SETUNE; 216 case FCmpInst::FCMP_TRUE: return ISD::SETTRUE; 217 default: llvm_unreachable("Invalid FCmp predicate opcode!"); 218 } 219 } 220 221 ISD::CondCode llvm::getFCmpCodeWithoutNaN(ISD::CondCode CC) { 222 switch (CC) { 223 case ISD::SETOEQ: case ISD::SETUEQ: return ISD::SETEQ; 224 case ISD::SETONE: case ISD::SETUNE: return ISD::SETNE; 225 case ISD::SETOLT: case ISD::SETULT: return ISD::SETLT; 226 case ISD::SETOLE: case ISD::SETULE: return ISD::SETLE; 227 case ISD::SETOGT: case ISD::SETUGT: return ISD::SETGT; 228 case ISD::SETOGE: case ISD::SETUGE: return ISD::SETGE; 229 default: return CC; 230 } 231 } 232 233 ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) { 234 switch (Pred) { 235 case ICmpInst::ICMP_EQ: return ISD::SETEQ; 236 case ICmpInst::ICMP_NE: return ISD::SETNE; 237 case ICmpInst::ICMP_SLE: return ISD::SETLE; 238 case ICmpInst::ICMP_ULE: return ISD::SETULE; 239 case ICmpInst::ICMP_SGE: return ISD::SETGE; 240 case ICmpInst::ICMP_UGE: return ISD::SETUGE; 241 case ICmpInst::ICMP_SLT: return ISD::SETLT; 242 case ICmpInst::ICMP_ULT: return ISD::SETULT; 243 case ICmpInst::ICMP_SGT: return ISD::SETGT; 244 case ICmpInst::ICMP_UGT: return ISD::SETUGT; 245 default: 246 llvm_unreachable("Invalid ICmp predicate opcode!"); 247 } 248 } 249 250 ICmpInst::Predicate llvm::getICmpCondCode(ISD::CondCode Pred) { 251 switch (Pred) { 252 case ISD::SETEQ: 253 return ICmpInst::ICMP_EQ; 254 case ISD::SETNE: 255 return ICmpInst::ICMP_NE; 256 case ISD::SETLE: 257 return ICmpInst::ICMP_SLE; 258 case ISD::SETULE: 259 return ICmpInst::ICMP_ULE; 260 case ISD::SETGE: 261 return ICmpInst::ICMP_SGE; 262 case ISD::SETUGE: 263 return ICmpInst::ICMP_UGE; 264 case ISD::SETLT: 265 return ICmpInst::ICMP_SLT; 266 case ISD::SETULT: 267 return ICmpInst::ICMP_ULT; 268 case ISD::SETGT: 269 return ICmpInst::ICMP_SGT; 270 case ISD::SETUGT: 271 return ICmpInst::ICMP_UGT; 272 default: 273 llvm_unreachable("Invalid ISD integer condition code!"); 274 } 275 } 276 277 static bool isNoopBitcast(Type *T1, Type *T2, 278 const TargetLoweringBase& TLI) { 279 return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) || 280 (isa<VectorType>(T1) && isa<VectorType>(T2) && 281 TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2))); 282 } 283 284 /// Look through operations that will be free to find the earliest source of 285 /// this value. 286 /// 287 /// @param ValLoc If V has aggregate type, we will be interested in a particular 288 /// scalar component. This records its address; the reverse of this list gives a 289 /// sequence of indices appropriate for an extractvalue to locate the important 290 /// value. This value is updated during the function and on exit will indicate 291 /// similar information for the Value returned. 292 /// 293 /// @param DataBits If this function looks through truncate instructions, this 294 /// will record the smallest size attained. 295 static const Value *getNoopInput(const Value *V, 296 SmallVectorImpl<unsigned> &ValLoc, 297 unsigned &DataBits, 298 const TargetLoweringBase &TLI, 299 const DataLayout &DL) { 300 while (true) { 301 // Try to look through V1; if V1 is not an instruction, it can't be looked 302 // through. 303 const Instruction *I = dyn_cast<Instruction>(V); 304 if (!I || I->getNumOperands() == 0) return V; 305 const Value *NoopInput = nullptr; 306 307 Value *Op = I->getOperand(0); 308 if (isa<BitCastInst>(I)) { 309 // Look through truly no-op bitcasts. 310 if (isNoopBitcast(Op->getType(), I->getType(), TLI)) 311 NoopInput = Op; 312 } else if (isa<GetElementPtrInst>(I)) { 313 // Look through getelementptr 314 if (cast<GetElementPtrInst>(I)->hasAllZeroIndices()) 315 NoopInput = Op; 316 } else if (isa<IntToPtrInst>(I)) { 317 // Look through inttoptr. 318 // Make sure this isn't a truncating or extending cast. We could 319 // support this eventually, but don't bother for now. 320 if (!isa<VectorType>(I->getType()) && 321 DL.getPointerSizeInBits() == 322 cast<IntegerType>(Op->getType())->getBitWidth()) 323 NoopInput = Op; 324 } else if (isa<PtrToIntInst>(I)) { 325 // Look through ptrtoint. 326 // Make sure this isn't a truncating or extending cast. We could 327 // support this eventually, but don't bother for now. 328 if (!isa<VectorType>(I->getType()) && 329 DL.getPointerSizeInBits() == 330 cast<IntegerType>(I->getType())->getBitWidth()) 331 NoopInput = Op; 332 } else if (isa<TruncInst>(I) && 333 TLI.allowTruncateForTailCall(Op->getType(), I->getType())) { 334 DataBits = 335 std::min((uint64_t)DataBits, 336 I->getType()->getPrimitiveSizeInBits().getFixedValue()); 337 NoopInput = Op; 338 } else if (auto *CB = dyn_cast<CallBase>(I)) { 339 const Value *ReturnedOp = CB->getReturnedArgOperand(); 340 if (ReturnedOp && isNoopBitcast(ReturnedOp->getType(), I->getType(), TLI)) 341 NoopInput = ReturnedOp; 342 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(V)) { 343 // Value may come from either the aggregate or the scalar 344 ArrayRef<unsigned> InsertLoc = IVI->getIndices(); 345 if (ValLoc.size() >= InsertLoc.size() && 346 std::equal(InsertLoc.begin(), InsertLoc.end(), ValLoc.rbegin())) { 347 // The type being inserted is a nested sub-type of the aggregate; we 348 // have to remove those initial indices to get the location we're 349 // interested in for the operand. 350 ValLoc.resize(ValLoc.size() - InsertLoc.size()); 351 NoopInput = IVI->getInsertedValueOperand(); 352 } else { 353 // The struct we're inserting into has the value we're interested in, no 354 // change of address. 355 NoopInput = Op; 356 } 357 } else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) { 358 // The part we're interested in will inevitably be some sub-section of the 359 // previous aggregate. Combine the two paths to obtain the true address of 360 // our element. 361 ArrayRef<unsigned> ExtractLoc = EVI->getIndices(); 362 ValLoc.append(ExtractLoc.rbegin(), ExtractLoc.rend()); 363 NoopInput = Op; 364 } 365 // Terminate if we couldn't find anything to look through. 366 if (!NoopInput) 367 return V; 368 369 V = NoopInput; 370 } 371 } 372 373 /// Return true if this scalar return value only has bits discarded on its path 374 /// from the "tail call" to the "ret". This includes the obvious noop 375 /// instructions handled by getNoopInput above as well as free truncations (or 376 /// extensions prior to the call). 377 static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal, 378 SmallVectorImpl<unsigned> &RetIndices, 379 SmallVectorImpl<unsigned> &CallIndices, 380 bool AllowDifferingSizes, 381 const TargetLoweringBase &TLI, 382 const DataLayout &DL) { 383 384 // Trace the sub-value needed by the return value as far back up the graph as 385 // possible, in the hope that it will intersect with the value produced by the 386 // call. In the simple case with no "returned" attribute, the hope is actually 387 // that we end up back at the tail call instruction itself. 388 unsigned BitsRequired = UINT_MAX; 389 RetVal = getNoopInput(RetVal, RetIndices, BitsRequired, TLI, DL); 390 391 // If this slot in the value returned is undef, it doesn't matter what the 392 // call puts there, it'll be fine. 393 if (isa<UndefValue>(RetVal)) 394 return true; 395 396 // Now do a similar search up through the graph to find where the value 397 // actually returned by the "tail call" comes from. In the simple case without 398 // a "returned" attribute, the search will be blocked immediately and the loop 399 // a Noop. 400 unsigned BitsProvided = UINT_MAX; 401 CallVal = getNoopInput(CallVal, CallIndices, BitsProvided, TLI, DL); 402 403 // There's no hope if we can't actually trace them to (the same part of!) the 404 // same value. 405 if (CallVal != RetVal || CallIndices != RetIndices) 406 return false; 407 408 // However, intervening truncates may have made the call non-tail. Make sure 409 // all the bits that are needed by the "ret" have been provided by the "tail 410 // call". FIXME: with sufficiently cunning bit-tracking, we could look through 411 // extensions too. 412 if (BitsProvided < BitsRequired || 413 (!AllowDifferingSizes && BitsProvided != BitsRequired)) 414 return false; 415 416 return true; 417 } 418 419 /// For an aggregate type, determine whether a given index is within bounds or 420 /// not. 421 static bool indexReallyValid(Type *T, unsigned Idx) { 422 if (ArrayType *AT = dyn_cast<ArrayType>(T)) 423 return Idx < AT->getNumElements(); 424 425 return Idx < cast<StructType>(T)->getNumElements(); 426 } 427 428 /// Move the given iterators to the next leaf type in depth first traversal. 429 /// 430 /// Performs a depth-first traversal of the type as specified by its arguments, 431 /// stopping at the next leaf node (which may be a legitimate scalar type or an 432 /// empty struct or array). 433 /// 434 /// @param SubTypes List of the partial components making up the type from 435 /// outermost to innermost non-empty aggregate. The element currently 436 /// represented is SubTypes.back()->getTypeAtIndex(Path.back() - 1). 437 /// 438 /// @param Path Set of extractvalue indices leading from the outermost type 439 /// (SubTypes[0]) to the leaf node currently represented. 440 /// 441 /// @returns true if a new type was found, false otherwise. Calling this 442 /// function again on a finished iterator will repeatedly return 443 /// false. SubTypes.back()->getTypeAtIndex(Path.back()) is either an empty 444 /// aggregate or a non-aggregate 445 static bool advanceToNextLeafType(SmallVectorImpl<Type *> &SubTypes, 446 SmallVectorImpl<unsigned> &Path) { 447 // First march back up the tree until we can successfully increment one of the 448 // coordinates in Path. 449 while (!Path.empty() && !indexReallyValid(SubTypes.back(), Path.back() + 1)) { 450 Path.pop_back(); 451 SubTypes.pop_back(); 452 } 453 454 // If we reached the top, then the iterator is done. 455 if (Path.empty()) 456 return false; 457 458 // We know there's *some* valid leaf now, so march back down the tree picking 459 // out the left-most element at each node. 460 ++Path.back(); 461 Type *DeeperType = 462 ExtractValueInst::getIndexedType(SubTypes.back(), Path.back()); 463 while (DeeperType->isAggregateType()) { 464 if (!indexReallyValid(DeeperType, 0)) 465 return true; 466 467 SubTypes.push_back(DeeperType); 468 Path.push_back(0); 469 470 DeeperType = ExtractValueInst::getIndexedType(DeeperType, 0); 471 } 472 473 return true; 474 } 475 476 /// Find the first non-empty, scalar-like type in Next and setup the iterator 477 /// components. 478 /// 479 /// Assuming Next is an aggregate of some kind, this function will traverse the 480 /// tree from left to right (i.e. depth-first) looking for the first 481 /// non-aggregate type which will play a role in function return. 482 /// 483 /// For example, if Next was {[0 x i64], {{}, i32, {}}, i32} then we would setup 484 /// Path as [1, 1] and SubTypes as [Next, {{}, i32, {}}] to represent the first 485 /// i32 in that type. 486 static bool firstRealType(Type *Next, SmallVectorImpl<Type *> &SubTypes, 487 SmallVectorImpl<unsigned> &Path) { 488 // First initialise the iterator components to the first "leaf" node 489 // (i.e. node with no valid sub-type at any index, so {} does count as a leaf 490 // despite nominally being an aggregate). 491 while (Type *FirstInner = ExtractValueInst::getIndexedType(Next, 0)) { 492 SubTypes.push_back(Next); 493 Path.push_back(0); 494 Next = FirstInner; 495 } 496 497 // If there's no Path now, Next was originally scalar already (or empty 498 // leaf). We're done. 499 if (Path.empty()) 500 return true; 501 502 // Otherwise, use normal iteration to keep looking through the tree until we 503 // find a non-aggregate type. 504 while (ExtractValueInst::getIndexedType(SubTypes.back(), Path.back()) 505 ->isAggregateType()) { 506 if (!advanceToNextLeafType(SubTypes, Path)) 507 return false; 508 } 509 510 return true; 511 } 512 513 /// Set the iterator data-structures to the next non-empty, non-aggregate 514 /// subtype. 515 static bool nextRealType(SmallVectorImpl<Type *> &SubTypes, 516 SmallVectorImpl<unsigned> &Path) { 517 do { 518 if (!advanceToNextLeafType(SubTypes, Path)) 519 return false; 520 521 assert(!Path.empty() && "found a leaf but didn't set the path?"); 522 } while (ExtractValueInst::getIndexedType(SubTypes.back(), Path.back()) 523 ->isAggregateType()); 524 525 return true; 526 } 527 528 529 /// Test if the given instruction is in a position to be optimized 530 /// with a tail-call. This roughly means that it's in a block with 531 /// a return and there's nothing that needs to be scheduled 532 /// between it and the return. 533 /// 534 /// This function only tests target-independent requirements. 535 bool llvm::isInTailCallPosition(const CallBase &Call, const TargetMachine &TM) { 536 const BasicBlock *ExitBB = Call.getParent(); 537 const Instruction *Term = ExitBB->getTerminator(); 538 const ReturnInst *Ret = dyn_cast<ReturnInst>(Term); 539 540 // The block must end in a return statement or unreachable. 541 // 542 // FIXME: Decline tailcall if it's not guaranteed and if the block ends in 543 // an unreachable, for now. The way tailcall optimization is currently 544 // implemented means it will add an epilogue followed by a jump. That is 545 // not profitable. Also, if the callee is a special function (e.g. 546 // longjmp on x86), it can end up causing miscompilation that has not 547 // been fully understood. 548 if (!Ret && ((!TM.Options.GuaranteedTailCallOpt && 549 Call.getCallingConv() != CallingConv::Tail && 550 Call.getCallingConv() != CallingConv::SwiftTail) || 551 !isa<UnreachableInst>(Term))) 552 return false; 553 554 // If I will have a chain, make sure no other instruction that will have a 555 // chain interposes between I and the return. 556 // Check for all calls including speculatable functions. 557 for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) { 558 if (&*BBI == &Call) 559 break; 560 // Debug info intrinsics do not get in the way of tail call optimization. 561 // Pseudo probe intrinsics do not block tail call optimization either. 562 if (BBI->isDebugOrPseudoInst()) 563 continue; 564 // A lifetime end, assume or noalias.decl intrinsic should not stop tail 565 // call optimization. 566 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI)) 567 if (II->getIntrinsicID() == Intrinsic::lifetime_end || 568 II->getIntrinsicID() == Intrinsic::assume || 569 II->getIntrinsicID() == Intrinsic::experimental_noalias_scope_decl) 570 continue; 571 if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() || 572 !isSafeToSpeculativelyExecute(&*BBI)) 573 return false; 574 } 575 576 const Function *F = ExitBB->getParent(); 577 return returnTypeIsEligibleForTailCall( 578 F, &Call, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering()); 579 } 580 581 bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I, 582 const ReturnInst *Ret, 583 const TargetLoweringBase &TLI, 584 bool *AllowDifferingSizes) { 585 // ADS may be null, so don't write to it directly. 586 bool DummyADS; 587 bool &ADS = AllowDifferingSizes ? *AllowDifferingSizes : DummyADS; 588 ADS = true; 589 590 AttrBuilder CallerAttrs(F->getContext(), F->getAttributes().getRetAttrs()); 591 AttrBuilder CalleeAttrs(F->getContext(), 592 cast<CallInst>(I)->getAttributes().getRetAttrs()); 593 594 // Following attributes are completely benign as far as calling convention 595 // goes, they shouldn't affect whether the call is a tail call. 596 for (const auto &Attr : {Attribute::Alignment, Attribute::Dereferenceable, 597 Attribute::DereferenceableOrNull, Attribute::NoAlias, 598 Attribute::NonNull, Attribute::NoUndef}) { 599 CallerAttrs.removeAttribute(Attr); 600 CalleeAttrs.removeAttribute(Attr); 601 } 602 603 if (CallerAttrs.contains(Attribute::ZExt)) { 604 if (!CalleeAttrs.contains(Attribute::ZExt)) 605 return false; 606 607 ADS = false; 608 CallerAttrs.removeAttribute(Attribute::ZExt); 609 CalleeAttrs.removeAttribute(Attribute::ZExt); 610 } else if (CallerAttrs.contains(Attribute::SExt)) { 611 if (!CalleeAttrs.contains(Attribute::SExt)) 612 return false; 613 614 ADS = false; 615 CallerAttrs.removeAttribute(Attribute::SExt); 616 CalleeAttrs.removeAttribute(Attribute::SExt); 617 } 618 619 // Drop sext and zext return attributes if the result is not used. 620 // This enables tail calls for code like: 621 // 622 // define void @caller() { 623 // entry: 624 // %unused_result = tail call zeroext i1 @callee() 625 // br label %retlabel 626 // retlabel: 627 // ret void 628 // } 629 if (I->use_empty()) { 630 CalleeAttrs.removeAttribute(Attribute::SExt); 631 CalleeAttrs.removeAttribute(Attribute::ZExt); 632 } 633 634 // If they're still different, there's some facet we don't understand 635 // (currently only "inreg", but in future who knows). It may be OK but the 636 // only safe option is to reject the tail call. 637 return CallerAttrs == CalleeAttrs; 638 } 639 640 /// Check whether B is a bitcast of a pointer type to another pointer type, 641 /// which is equal to A. 642 static bool isPointerBitcastEqualTo(const Value *A, const Value *B) { 643 assert(A && B && "Expected non-null inputs!"); 644 645 auto *BitCastIn = dyn_cast<BitCastInst>(B); 646 647 if (!BitCastIn) 648 return false; 649 650 if (!A->getType()->isPointerTy() || !B->getType()->isPointerTy()) 651 return false; 652 653 return A == BitCastIn->getOperand(0); 654 } 655 656 bool llvm::returnTypeIsEligibleForTailCall(const Function *F, 657 const Instruction *I, 658 const ReturnInst *Ret, 659 const TargetLoweringBase &TLI) { 660 // If the block ends with a void return or unreachable, it doesn't matter 661 // what the call's return type is. 662 if (!Ret || Ret->getNumOperands() == 0) return true; 663 664 // If the return value is undef, it doesn't matter what the call's 665 // return type is. 666 if (isa<UndefValue>(Ret->getOperand(0))) return true; 667 668 // Make sure the attributes attached to each return are compatible. 669 bool AllowDifferingSizes; 670 if (!attributesPermitTailCall(F, I, Ret, TLI, &AllowDifferingSizes)) 671 return false; 672 673 const Value *RetVal = Ret->getOperand(0), *CallVal = I; 674 // Intrinsic like llvm.memcpy has no return value, but the expanded 675 // libcall may or may not have return value. On most platforms, it 676 // will be expanded as memcpy in libc, which returns the first 677 // argument. On other platforms like arm-none-eabi, memcpy may be 678 // expanded as library call without return value, like __aeabi_memcpy. 679 const CallInst *Call = cast<CallInst>(I); 680 if (Function *F = Call->getCalledFunction()) { 681 Intrinsic::ID IID = F->getIntrinsicID(); 682 if (((IID == Intrinsic::memcpy && 683 TLI.getLibcallName(RTLIB::MEMCPY) == StringRef("memcpy")) || 684 (IID == Intrinsic::memmove && 685 TLI.getLibcallName(RTLIB::MEMMOVE) == StringRef("memmove")) || 686 (IID == Intrinsic::memset && 687 TLI.getLibcallName(RTLIB::MEMSET) == StringRef("memset"))) && 688 (RetVal == Call->getArgOperand(0) || 689 isPointerBitcastEqualTo(RetVal, Call->getArgOperand(0)))) 690 return true; 691 } 692 693 SmallVector<unsigned, 4> RetPath, CallPath; 694 SmallVector<Type *, 4> RetSubTypes, CallSubTypes; 695 696 bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath); 697 bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath); 698 699 // Nothing's actually returned, it doesn't matter what the callee put there 700 // it's a valid tail call. 701 if (RetEmpty) 702 return true; 703 704 // Iterate pairwise through each of the value types making up the tail call 705 // and the corresponding return. For each one we want to know whether it's 706 // essentially going directly from the tail call to the ret, via operations 707 // that end up not generating any code. 708 // 709 // We allow a certain amount of covariance here. For example it's permitted 710 // for the tail call to define more bits than the ret actually cares about 711 // (e.g. via a truncate). 712 do { 713 if (CallEmpty) { 714 // We've exhausted the values produced by the tail call instruction, the 715 // rest are essentially undef. The type doesn't really matter, but we need 716 // *something*. 717 Type *SlotType = 718 ExtractValueInst::getIndexedType(RetSubTypes.back(), RetPath.back()); 719 CallVal = UndefValue::get(SlotType); 720 } 721 722 // The manipulations performed when we're looking through an insertvalue or 723 // an extractvalue would happen at the front of the RetPath list, so since 724 // we have to copy it anyway it's more efficient to create a reversed copy. 725 SmallVector<unsigned, 4> TmpRetPath(llvm::reverse(RetPath)); 726 SmallVector<unsigned, 4> TmpCallPath(llvm::reverse(CallPath)); 727 728 // Finally, we can check whether the value produced by the tail call at this 729 // index is compatible with the value we return. 730 if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath, 731 AllowDifferingSizes, TLI, 732 F->getParent()->getDataLayout())) 733 return false; 734 735 CallEmpty = !nextRealType(CallSubTypes, CallPath); 736 } while(nextRealType(RetSubTypes, RetPath)); 737 738 return true; 739 } 740 741 static void collectEHScopeMembers( 742 DenseMap<const MachineBasicBlock *, int> &EHScopeMembership, int EHScope, 743 const MachineBasicBlock *MBB) { 744 SmallVector<const MachineBasicBlock *, 16> Worklist = {MBB}; 745 while (!Worklist.empty()) { 746 const MachineBasicBlock *Visiting = Worklist.pop_back_val(); 747 // Don't follow blocks which start new scopes. 748 if (Visiting->isEHPad() && Visiting != MBB) 749 continue; 750 751 // Add this MBB to our scope. 752 auto P = EHScopeMembership.insert(std::make_pair(Visiting, EHScope)); 753 754 // Don't revisit blocks. 755 if (!P.second) { 756 assert(P.first->second == EHScope && "MBB is part of two scopes!"); 757 continue; 758 } 759 760 // Returns are boundaries where scope transfer can occur, don't follow 761 // successors. 762 if (Visiting->isEHScopeReturnBlock()) 763 continue; 764 765 append_range(Worklist, Visiting->successors()); 766 } 767 } 768 769 DenseMap<const MachineBasicBlock *, int> 770 llvm::getEHScopeMembership(const MachineFunction &MF) { 771 DenseMap<const MachineBasicBlock *, int> EHScopeMembership; 772 773 // We don't have anything to do if there aren't any EH pads. 774 if (!MF.hasEHScopes()) 775 return EHScopeMembership; 776 777 int EntryBBNumber = MF.front().getNumber(); 778 bool IsSEH = isAsynchronousEHPersonality( 779 classifyEHPersonality(MF.getFunction().getPersonalityFn())); 780 781 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); 782 SmallVector<const MachineBasicBlock *, 16> EHScopeBlocks; 783 SmallVector<const MachineBasicBlock *, 16> UnreachableBlocks; 784 SmallVector<const MachineBasicBlock *, 16> SEHCatchPads; 785 SmallVector<std::pair<const MachineBasicBlock *, int>, 16> CatchRetSuccessors; 786 for (const MachineBasicBlock &MBB : MF) { 787 if (MBB.isEHScopeEntry()) { 788 EHScopeBlocks.push_back(&MBB); 789 } else if (IsSEH && MBB.isEHPad()) { 790 SEHCatchPads.push_back(&MBB); 791 } else if (MBB.pred_empty()) { 792 UnreachableBlocks.push_back(&MBB); 793 } 794 795 MachineBasicBlock::const_iterator MBBI = MBB.getFirstTerminator(); 796 797 // CatchPads are not scopes for SEH so do not consider CatchRet to 798 // transfer control to another scope. 799 if (MBBI == MBB.end() || MBBI->getOpcode() != TII->getCatchReturnOpcode()) 800 continue; 801 802 // FIXME: SEH CatchPads are not necessarily in the parent function: 803 // they could be inside a finally block. 804 const MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB(); 805 const MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB(); 806 CatchRetSuccessors.push_back( 807 {Successor, IsSEH ? EntryBBNumber : SuccessorColor->getNumber()}); 808 } 809 810 // We don't have anything to do if there aren't any EH pads. 811 if (EHScopeBlocks.empty()) 812 return EHScopeMembership; 813 814 // Identify all the basic blocks reachable from the function entry. 815 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, &MF.front()); 816 // All blocks not part of a scope are in the parent function. 817 for (const MachineBasicBlock *MBB : UnreachableBlocks) 818 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB); 819 // Next, identify all the blocks inside the scopes. 820 for (const MachineBasicBlock *MBB : EHScopeBlocks) 821 collectEHScopeMembers(EHScopeMembership, MBB->getNumber(), MBB); 822 // SEH CatchPads aren't really scopes, handle them separately. 823 for (const MachineBasicBlock *MBB : SEHCatchPads) 824 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB); 825 // Finally, identify all the targets of a catchret. 826 for (std::pair<const MachineBasicBlock *, int> CatchRetPair : 827 CatchRetSuccessors) 828 collectEHScopeMembers(EHScopeMembership, CatchRetPair.second, 829 CatchRetPair.first); 830 return EHScopeMembership; 831 } 832