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 bool ReturnsFirstArg) { 537 const BasicBlock *ExitBB = Call.getParent(); 538 const Instruction *Term = ExitBB->getTerminator(); 539 const ReturnInst *Ret = dyn_cast<ReturnInst>(Term); 540 541 // The block must end in a return statement or unreachable. 542 // 543 // FIXME: Decline tailcall if it's not guaranteed and if the block ends in 544 // an unreachable, for now. The way tailcall optimization is currently 545 // implemented means it will add an epilogue followed by a jump. That is 546 // not profitable. Also, if the callee is a special function (e.g. 547 // longjmp on x86), it can end up causing miscompilation that has not 548 // been fully understood. 549 if (!Ret && ((!TM.Options.GuaranteedTailCallOpt && 550 Call.getCallingConv() != CallingConv::Tail && 551 Call.getCallingConv() != CallingConv::SwiftTail) || 552 !isa<UnreachableInst>(Term))) 553 return false; 554 555 // If I will have a chain, make sure no other instruction that will have a 556 // chain interposes between I and the return. 557 // Check for all calls including speculatable functions. 558 for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) { 559 if (&*BBI == &Call) 560 break; 561 // Debug info intrinsics do not get in the way of tail call optimization. 562 // Pseudo probe intrinsics do not block tail call optimization either. 563 if (BBI->isDebugOrPseudoInst()) 564 continue; 565 // A lifetime end, assume or noalias.decl intrinsic should not stop tail 566 // call optimization. 567 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI)) 568 if (II->getIntrinsicID() == Intrinsic::lifetime_end || 569 II->getIntrinsicID() == Intrinsic::assume || 570 II->getIntrinsicID() == Intrinsic::experimental_noalias_scope_decl) 571 continue; 572 if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() || 573 !isSafeToSpeculativelyExecute(&*BBI)) 574 return false; 575 } 576 577 const Function *F = ExitBB->getParent(); 578 return returnTypeIsEligibleForTailCall( 579 F, &Call, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering(), 580 ReturnsFirstArg); 581 } 582 583 bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I, 584 const ReturnInst *Ret, 585 const TargetLoweringBase &TLI, 586 bool *AllowDifferingSizes) { 587 // ADS may be null, so don't write to it directly. 588 bool DummyADS; 589 bool &ADS = AllowDifferingSizes ? *AllowDifferingSizes : DummyADS; 590 ADS = true; 591 592 AttrBuilder CallerAttrs(F->getContext(), F->getAttributes().getRetAttrs()); 593 AttrBuilder CalleeAttrs(F->getContext(), 594 cast<CallInst>(I)->getAttributes().getRetAttrs()); 595 596 // Following attributes are completely benign as far as calling convention 597 // goes, they shouldn't affect whether the call is a tail call. 598 for (const auto &Attr : 599 {Attribute::Alignment, Attribute::Dereferenceable, 600 Attribute::DereferenceableOrNull, Attribute::NoAlias, 601 Attribute::NonNull, Attribute::NoUndef, Attribute::Range}) { 602 CallerAttrs.removeAttribute(Attr); 603 CalleeAttrs.removeAttribute(Attr); 604 } 605 606 if (CallerAttrs.contains(Attribute::ZExt)) { 607 if (!CalleeAttrs.contains(Attribute::ZExt)) 608 return false; 609 610 ADS = false; 611 CallerAttrs.removeAttribute(Attribute::ZExt); 612 CalleeAttrs.removeAttribute(Attribute::ZExt); 613 } else if (CallerAttrs.contains(Attribute::SExt)) { 614 if (!CalleeAttrs.contains(Attribute::SExt)) 615 return false; 616 617 ADS = false; 618 CallerAttrs.removeAttribute(Attribute::SExt); 619 CalleeAttrs.removeAttribute(Attribute::SExt); 620 } 621 622 // Drop sext and zext return attributes if the result is not used. 623 // This enables tail calls for code like: 624 // 625 // define void @caller() { 626 // entry: 627 // %unused_result = tail call zeroext i1 @callee() 628 // br label %retlabel 629 // retlabel: 630 // ret void 631 // } 632 if (I->use_empty()) { 633 CalleeAttrs.removeAttribute(Attribute::SExt); 634 CalleeAttrs.removeAttribute(Attribute::ZExt); 635 } 636 637 // If they're still different, there's some facet we don't understand 638 // (currently only "inreg", but in future who knows). It may be OK but the 639 // only safe option is to reject the tail call. 640 return CallerAttrs == CalleeAttrs; 641 } 642 643 bool llvm::returnTypeIsEligibleForTailCall(const Function *F, 644 const Instruction *I, 645 const ReturnInst *Ret, 646 const TargetLoweringBase &TLI, 647 bool ReturnsFirstArg) { 648 // If the block ends with a void return or unreachable, it doesn't matter 649 // what the call's return type is. 650 if (!Ret || Ret->getNumOperands() == 0) return true; 651 652 // If the return value is undef, it doesn't matter what the call's 653 // return type is. 654 if (isa<UndefValue>(Ret->getOperand(0))) return true; 655 656 // Make sure the attributes attached to each return are compatible. 657 bool AllowDifferingSizes; 658 if (!attributesPermitTailCall(F, I, Ret, TLI, &AllowDifferingSizes)) 659 return false; 660 661 // If the return value is the first argument of the call. 662 if (ReturnsFirstArg) 663 return true; 664 665 const Value *RetVal = Ret->getOperand(0), *CallVal = I; 666 SmallVector<unsigned, 4> RetPath, CallPath; 667 SmallVector<Type *, 4> RetSubTypes, CallSubTypes; 668 669 bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath); 670 bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath); 671 672 // Nothing's actually returned, it doesn't matter what the callee put there 673 // it's a valid tail call. 674 if (RetEmpty) 675 return true; 676 677 // Iterate pairwise through each of the value types making up the tail call 678 // and the corresponding return. For each one we want to know whether it's 679 // essentially going directly from the tail call to the ret, via operations 680 // that end up not generating any code. 681 // 682 // We allow a certain amount of covariance here. For example it's permitted 683 // for the tail call to define more bits than the ret actually cares about 684 // (e.g. via a truncate). 685 do { 686 if (CallEmpty) { 687 // We've exhausted the values produced by the tail call instruction, the 688 // rest are essentially undef. The type doesn't really matter, but we need 689 // *something*. 690 Type *SlotType = 691 ExtractValueInst::getIndexedType(RetSubTypes.back(), RetPath.back()); 692 CallVal = UndefValue::get(SlotType); 693 } 694 695 // The manipulations performed when we're looking through an insertvalue or 696 // an extractvalue would happen at the front of the RetPath list, so since 697 // we have to copy it anyway it's more efficient to create a reversed copy. 698 SmallVector<unsigned, 4> TmpRetPath(llvm::reverse(RetPath)); 699 SmallVector<unsigned, 4> TmpCallPath(llvm::reverse(CallPath)); 700 701 // Finally, we can check whether the value produced by the tail call at this 702 // index is compatible with the value we return. 703 if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath, 704 AllowDifferingSizes, TLI, 705 F->getDataLayout())) 706 return false; 707 708 CallEmpty = !nextRealType(CallSubTypes, CallPath); 709 } while(nextRealType(RetSubTypes, RetPath)); 710 711 return true; 712 } 713 714 bool llvm::funcReturnsFirstArgOfCall(const CallInst &CI) { 715 const ReturnInst *Ret = dyn_cast<ReturnInst>(CI.getParent()->getTerminator()); 716 Value *RetVal = Ret ? Ret->getReturnValue() : nullptr; 717 bool ReturnsFirstArg = false; 718 if (RetVal && ((RetVal == CI.getArgOperand(0)))) 719 ReturnsFirstArg = true; 720 return ReturnsFirstArg; 721 } 722 723 static void collectEHScopeMembers( 724 DenseMap<const MachineBasicBlock *, int> &EHScopeMembership, int EHScope, 725 const MachineBasicBlock *MBB) { 726 SmallVector<const MachineBasicBlock *, 16> Worklist = {MBB}; 727 while (!Worklist.empty()) { 728 const MachineBasicBlock *Visiting = Worklist.pop_back_val(); 729 // Don't follow blocks which start new scopes. 730 if (Visiting->isEHPad() && Visiting != MBB) 731 continue; 732 733 // Add this MBB to our scope. 734 auto P = EHScopeMembership.insert(std::make_pair(Visiting, EHScope)); 735 736 // Don't revisit blocks. 737 if (!P.second) { 738 assert(P.first->second == EHScope && "MBB is part of two scopes!"); 739 continue; 740 } 741 742 // Returns are boundaries where scope transfer can occur, don't follow 743 // successors. 744 if (Visiting->isEHScopeReturnBlock()) 745 continue; 746 747 append_range(Worklist, Visiting->successors()); 748 } 749 } 750 751 DenseMap<const MachineBasicBlock *, int> 752 llvm::getEHScopeMembership(const MachineFunction &MF) { 753 DenseMap<const MachineBasicBlock *, int> EHScopeMembership; 754 755 // We don't have anything to do if there aren't any EH pads. 756 if (!MF.hasEHScopes()) 757 return EHScopeMembership; 758 759 int EntryBBNumber = MF.front().getNumber(); 760 bool IsSEH = isAsynchronousEHPersonality( 761 classifyEHPersonality(MF.getFunction().getPersonalityFn())); 762 763 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); 764 SmallVector<const MachineBasicBlock *, 16> EHScopeBlocks; 765 SmallVector<const MachineBasicBlock *, 16> UnreachableBlocks; 766 SmallVector<const MachineBasicBlock *, 16> SEHCatchPads; 767 SmallVector<std::pair<const MachineBasicBlock *, int>, 16> CatchRetSuccessors; 768 for (const MachineBasicBlock &MBB : MF) { 769 if (MBB.isEHScopeEntry()) { 770 EHScopeBlocks.push_back(&MBB); 771 } else if (IsSEH && MBB.isEHPad()) { 772 SEHCatchPads.push_back(&MBB); 773 } else if (MBB.pred_empty()) { 774 UnreachableBlocks.push_back(&MBB); 775 } 776 777 MachineBasicBlock::const_iterator MBBI = MBB.getFirstTerminator(); 778 779 // CatchPads are not scopes for SEH so do not consider CatchRet to 780 // transfer control to another scope. 781 if (MBBI == MBB.end() || MBBI->getOpcode() != TII->getCatchReturnOpcode()) 782 continue; 783 784 // FIXME: SEH CatchPads are not necessarily in the parent function: 785 // they could be inside a finally block. 786 const MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB(); 787 const MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB(); 788 CatchRetSuccessors.push_back( 789 {Successor, IsSEH ? EntryBBNumber : SuccessorColor->getNumber()}); 790 } 791 792 // We don't have anything to do if there aren't any EH pads. 793 if (EHScopeBlocks.empty()) 794 return EHScopeMembership; 795 796 // Identify all the basic blocks reachable from the function entry. 797 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, &MF.front()); 798 // All blocks not part of a scope are in the parent function. 799 for (const MachineBasicBlock *MBB : UnreachableBlocks) 800 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB); 801 // Next, identify all the blocks inside the scopes. 802 for (const MachineBasicBlock *MBB : EHScopeBlocks) 803 collectEHScopeMembers(EHScopeMembership, MBB->getNumber(), MBB); 804 // SEH CatchPads aren't really scopes, handle them separately. 805 for (const MachineBasicBlock *MBB : SEHCatchPads) 806 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB); 807 // Finally, identify all the targets of a catchret. 808 for (std::pair<const MachineBasicBlock *, int> CatchRetPair : 809 CatchRetSuccessors) 810 collectEHScopeMembers(EHScopeMembership, CatchRetPair.second, 811 CatchRetPair.first); 812 return EHScopeMembership; 813 } 814