LLVM  10.0.0svn
Analysis.cpp
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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"
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/LLVMContext.h"
25 #include "llvm/IR/Module.h"
29 
30 using namespace llvm;
31 
32 /// Compute the linearized index of a member in a nested aggregate/struct/array
33 /// by recursing and accumulating CurIndex as long as there are indices in the
34 /// index list.
36  const unsigned *Indices,
37  const unsigned *IndicesEnd,
38  unsigned CurIndex) {
39  // Base case: We're done.
40  if (Indices && Indices == IndicesEnd)
41  return CurIndex;
42 
43  // Given a struct type, recursively traverse the elements.
44  if (StructType *STy = dyn_cast<StructType>(Ty)) {
45  for (StructType::element_iterator EB = STy->element_begin(),
46  EI = EB,
47  EE = STy->element_end();
48  EI != EE; ++EI) {
49  if (Indices && *Indices == unsigned(EI - EB))
50  return ComputeLinearIndex(*EI, Indices+1, IndicesEnd, CurIndex);
51  CurIndex = ComputeLinearIndex(*EI, nullptr, nullptr, CurIndex);
52  }
53  assert(!Indices && "Unexpected out of bound");
54  return CurIndex;
55  }
56  // Given an array type, recursively traverse the elements.
57  else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
58  Type *EltTy = ATy->getElementType();
59  unsigned NumElts = ATy->getNumElements();
60  // Compute the Linear offset when jumping one element of the array
61  unsigned EltLinearOffset = ComputeLinearIndex(EltTy, nullptr, nullptr, 0);
62  if (Indices) {
63  assert(*Indices < NumElts && "Unexpected out of bound");
64  // If the indice is inside the array, compute the index to the requested
65  // elt and recurse inside the element with the end of the indices list
66  CurIndex += EltLinearOffset* *Indices;
67  return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
68  }
69  CurIndex += EltLinearOffset*NumElts;
70  return CurIndex;
71  }
72  // We haven't found the type we're looking for, so keep searching.
73  return CurIndex + 1;
74 }
75 
76 /// ComputeValueVTs - Given an LLVM IR type, compute a sequence of
77 /// EVTs that represent all the individual underlying
78 /// non-aggregate types that comprise it.
79 ///
80 /// If Offsets is non-null, it points to a vector to be filled in
81 /// with the in-memory offsets of each of the individual values.
82 ///
83 void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
84  Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
85  SmallVectorImpl<EVT> *MemVTs,
87  uint64_t StartingOffset) {
88  // Given a struct type, recursively traverse the elements.
89  if (StructType *STy = dyn_cast<StructType>(Ty)) {
90  const StructLayout *SL = DL.getStructLayout(STy);
91  for (StructType::element_iterator EB = STy->element_begin(),
92  EI = EB,
93  EE = STy->element_end();
94  EI != EE; ++EI)
95  ComputeValueVTs(TLI, DL, *EI, ValueVTs, MemVTs, Offsets,
96  StartingOffset + SL->getElementOffset(EI - EB));
97  return;
98  }
99  // Given an array type, recursively traverse the elements.
100  if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
101  Type *EltTy = ATy->getElementType();
102  uint64_t EltSize = DL.getTypeAllocSize(EltTy);
103  for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
104  ComputeValueVTs(TLI, DL, EltTy, ValueVTs, MemVTs, Offsets,
105  StartingOffset + i * EltSize);
106  return;
107  }
108  // Interpret void as zero return values.
109  if (Ty->isVoidTy())
110  return;
111  // Base case: we can get an EVT for this LLVM IR type.
112  ValueVTs.push_back(TLI.getValueType(DL, Ty));
113  if (MemVTs)
114  MemVTs->push_back(TLI.getMemValueType(DL, Ty));
115  if (Offsets)
116  Offsets->push_back(StartingOffset);
117 }
118 
120  Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
122  uint64_t StartingOffset) {
123  return ComputeValueVTs(TLI, DL, Ty, ValueVTs, /*MemVTs=*/nullptr, Offsets,
124  StartingOffset);
125 }
126 
128  SmallVectorImpl<LLT> &ValueTys,
130  uint64_t StartingOffset) {
131  // Given a struct type, recursively traverse the elements.
132  if (StructType *STy = dyn_cast<StructType>(&Ty)) {
133  const StructLayout *SL = DL.getStructLayout(STy);
134  for (unsigned I = 0, E = STy->getNumElements(); I != E; ++I)
135  computeValueLLTs(DL, *STy->getElementType(I), ValueTys, Offsets,
136  StartingOffset + SL->getElementOffset(I));
137  return;
138  }
139  // Given an array type, recursively traverse the elements.
140  if (ArrayType *ATy = dyn_cast<ArrayType>(&Ty)) {
141  Type *EltTy = ATy->getElementType();
142  uint64_t EltSize = DL.getTypeAllocSize(EltTy);
143  for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
144  computeValueLLTs(DL, *EltTy, ValueTys, Offsets,
145  StartingOffset + i * EltSize);
146  return;
147  }
148  // Interpret void as zero return values.
149  if (Ty.isVoidTy())
150  return;
151  // Base case: we can get an LLT for this LLVM IR type.
152  ValueTys.push_back(getLLTForType(Ty, DL));
153  if (Offsets != nullptr)
154  Offsets->push_back(StartingOffset * 8);
155 }
156 
157 /// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
159  V = V->stripPointerCasts();
160  GlobalValue *GV = dyn_cast<GlobalValue>(V);
162 
163  if (Var && Var->getName() == "llvm.eh.catch.all.value") {
164  assert(Var->hasInitializer() &&
165  "The EH catch-all value must have an initializer");
166  Value *Init = Var->getInitializer();
167  GV = dyn_cast<GlobalValue>(Init);
168  if (!GV) V = cast<ConstantPointerNull>(Init);
169  }
170 
171  assert((GV || isa<ConstantPointerNull>(V)) &&
172  "TypeInfo must be a global variable or NULL");
173  return GV;
174 }
175 
176 /// hasInlineAsmMemConstraint - Return true if the inline asm instruction being
177 /// processed uses a memory 'm' constraint.
178 bool
180  const TargetLowering &TLI) {
181  for (unsigned i = 0, e = CInfos.size(); i != e; ++i) {
182  InlineAsm::ConstraintInfo &CI = CInfos[i];
183  for (unsigned j = 0, ee = CI.Codes.size(); j != ee; ++j) {
185  if (CType == TargetLowering::C_Memory)
186  return true;
187  }
188 
189  // Indirect operand accesses access memory.
190  if (CI.isIndirect)
191  return true;
192  }
193 
194  return false;
195 }
196 
197 /// getFCmpCondCode - Return the ISD condition code corresponding to
198 /// the given LLVM IR floating-point condition code. This includes
199 /// consideration of global floating-point math flags.
200 ///
202  switch (Pred) {
203  case FCmpInst::FCMP_FALSE: return ISD::SETFALSE;
204  case FCmpInst::FCMP_OEQ: return ISD::SETOEQ;
205  case FCmpInst::FCMP_OGT: return ISD::SETOGT;
206  case FCmpInst::FCMP_OGE: return ISD::SETOGE;
207  case FCmpInst::FCMP_OLT: return ISD::SETOLT;
208  case FCmpInst::FCMP_OLE: return ISD::SETOLE;
209  case FCmpInst::FCMP_ONE: return ISD::SETONE;
210  case FCmpInst::FCMP_ORD: return ISD::SETO;
211  case FCmpInst::FCMP_UNO: return ISD::SETUO;
212  case FCmpInst::FCMP_UEQ: return ISD::SETUEQ;
213  case FCmpInst::FCMP_UGT: return ISD::SETUGT;
214  case FCmpInst::FCMP_UGE: return ISD::SETUGE;
215  case FCmpInst::FCMP_ULT: return ISD::SETULT;
216  case FCmpInst::FCMP_ULE: return ISD::SETULE;
217  case FCmpInst::FCMP_UNE: return ISD::SETUNE;
218  case FCmpInst::FCMP_TRUE: return ISD::SETTRUE;
219  default: llvm_unreachable("Invalid FCmp predicate opcode!");
220  }
221 }
222 
224  switch (CC) {
225  case ISD::SETOEQ: case ISD::SETUEQ: return ISD::SETEQ;
226  case ISD::SETONE: case ISD::SETUNE: return ISD::SETNE;
227  case ISD::SETOLT: case ISD::SETULT: return ISD::SETLT;
228  case ISD::SETOLE: case ISD::SETULE: return ISD::SETLE;
229  case ISD::SETOGT: case ISD::SETUGT: return ISD::SETGT;
230  case ISD::SETOGE: case ISD::SETUGE: return ISD::SETGE;
231  default: return CC;
232  }
233 }
234 
235 /// getICmpCondCode - Return the ISD condition code corresponding to
236 /// the given LLVM IR integer condition code.
237 ///
239  switch (Pred) {
240  case ICmpInst::ICMP_EQ: return ISD::SETEQ;
241  case ICmpInst::ICMP_NE: return ISD::SETNE;
242  case ICmpInst::ICMP_SLE: return ISD::SETLE;
243  case ICmpInst::ICMP_ULE: return ISD::SETULE;
244  case ICmpInst::ICMP_SGE: return ISD::SETGE;
245  case ICmpInst::ICMP_UGE: return ISD::SETUGE;
246  case ICmpInst::ICMP_SLT: return ISD::SETLT;
247  case ICmpInst::ICMP_ULT: return ISD::SETULT;
248  case ICmpInst::ICMP_SGT: return ISD::SETGT;
249  case ICmpInst::ICMP_UGT: return ISD::SETUGT;
250  default:
251  llvm_unreachable("Invalid ICmp predicate opcode!");
252  }
253 }
254 
255 static bool isNoopBitcast(Type *T1, Type *T2,
256  const TargetLoweringBase& TLI) {
257  return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) ||
258  (isa<VectorType>(T1) && isa<VectorType>(T2) &&
259  TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2)));
260 }
261 
262 /// Look through operations that will be free to find the earliest source of
263 /// this value.
264 ///
265 /// @param ValLoc If V has aggegate type, we will be interested in a particular
266 /// scalar component. This records its address; the reverse of this list gives a
267 /// sequence of indices appropriate for an extractvalue to locate the important
268 /// value. This value is updated during the function and on exit will indicate
269 /// similar information for the Value returned.
270 ///
271 /// @param DataBits If this function looks through truncate instructions, this
272 /// will record the smallest size attained.
273 static const Value *getNoopInput(const Value *V,
275  unsigned &DataBits,
276  const TargetLoweringBase &TLI,
277  const DataLayout &DL) {
278  while (true) {
279  // Try to look through V1; if V1 is not an instruction, it can't be looked
280  // through.
281  const Instruction *I = dyn_cast<Instruction>(V);
282  if (!I || I->getNumOperands() == 0) return V;
283  const Value *NoopInput = nullptr;
284 
285  Value *Op = I->getOperand(0);
286  if (isa<BitCastInst>(I)) {
287  // Look through truly no-op bitcasts.
288  if (isNoopBitcast(Op->getType(), I->getType(), TLI))
289  NoopInput = Op;
290  } else if (isa<GetElementPtrInst>(I)) {
291  // Look through getelementptr
292  if (cast<GetElementPtrInst>(I)->hasAllZeroIndices())
293  NoopInput = Op;
294  } else if (isa<IntToPtrInst>(I)) {
295  // Look through inttoptr.
296  // Make sure this isn't a truncating or extending cast. We could
297  // support this eventually, but don't bother for now.
298  if (!isa<VectorType>(I->getType()) &&
299  DL.getPointerSizeInBits() ==
300  cast<IntegerType>(Op->getType())->getBitWidth())
301  NoopInput = Op;
302  } else if (isa<PtrToIntInst>(I)) {
303  // Look through ptrtoint.
304  // Make sure this isn't a truncating or extending cast. We could
305  // support this eventually, but don't bother for now.
306  if (!isa<VectorType>(I->getType()) &&
307  DL.getPointerSizeInBits() ==
308  cast<IntegerType>(I->getType())->getBitWidth())
309  NoopInput = Op;
310  } else if (isa<TruncInst>(I) &&
311  TLI.allowTruncateForTailCall(Op->getType(), I->getType())) {
312  DataBits = std::min(DataBits, I->getType()->getPrimitiveSizeInBits());
313  NoopInput = Op;
314  } else if (auto CS = ImmutableCallSite(I)) {
315  const Value *ReturnedOp = CS.getReturnedArgOperand();
316  if (ReturnedOp && isNoopBitcast(ReturnedOp->getType(), I->getType(), TLI))
317  NoopInput = ReturnedOp;
318  } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(V)) {
319  // Value may come from either the aggregate or the scalar
320  ArrayRef<unsigned> InsertLoc = IVI->getIndices();
321  if (ValLoc.size() >= InsertLoc.size() &&
322  std::equal(InsertLoc.begin(), InsertLoc.end(), ValLoc.rbegin())) {
323  // The type being inserted is a nested sub-type of the aggregate; we
324  // have to remove those initial indices to get the location we're
325  // interested in for the operand.
326  ValLoc.resize(ValLoc.size() - InsertLoc.size());
327  NoopInput = IVI->getInsertedValueOperand();
328  } else {
329  // The struct we're inserting into has the value we're interested in, no
330  // change of address.
331  NoopInput = Op;
332  }
333  } else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
334  // The part we're interested in will inevitably be some sub-section of the
335  // previous aggregate. Combine the two paths to obtain the true address of
336  // our element.
337  ArrayRef<unsigned> ExtractLoc = EVI->getIndices();
338  ValLoc.append(ExtractLoc.rbegin(), ExtractLoc.rend());
339  NoopInput = Op;
340  }
341  // Terminate if we couldn't find anything to look through.
342  if (!NoopInput)
343  return V;
344 
345  V = NoopInput;
346  }
347 }
348 
349 /// Return true if this scalar return value only has bits discarded on its path
350 /// from the "tail call" to the "ret". This includes the obvious noop
351 /// instructions handled by getNoopInput above as well as free truncations (or
352 /// extensions prior to the call).
353 static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal,
354  SmallVectorImpl<unsigned> &RetIndices,
355  SmallVectorImpl<unsigned> &CallIndices,
356  bool AllowDifferingSizes,
357  const TargetLoweringBase &TLI,
358  const DataLayout &DL) {
359 
360  // Trace the sub-value needed by the return value as far back up the graph as
361  // possible, in the hope that it will intersect with the value produced by the
362  // call. In the simple case with no "returned" attribute, the hope is actually
363  // that we end up back at the tail call instruction itself.
364  unsigned BitsRequired = UINT_MAX;
365  RetVal = getNoopInput(RetVal, RetIndices, BitsRequired, TLI, DL);
366 
367  // If this slot in the value returned is undef, it doesn't matter what the
368  // call puts there, it'll be fine.
369  if (isa<UndefValue>(RetVal))
370  return true;
371 
372  // Now do a similar search up through the graph to find where the value
373  // actually returned by the "tail call" comes from. In the simple case without
374  // a "returned" attribute, the search will be blocked immediately and the loop
375  // a Noop.
376  unsigned BitsProvided = UINT_MAX;
377  CallVal = getNoopInput(CallVal, CallIndices, BitsProvided, TLI, DL);
378 
379  // There's no hope if we can't actually trace them to (the same part of!) the
380  // same value.
381  if (CallVal != RetVal || CallIndices != RetIndices)
382  return false;
383 
384  // However, intervening truncates may have made the call non-tail. Make sure
385  // all the bits that are needed by the "ret" have been provided by the "tail
386  // call". FIXME: with sufficiently cunning bit-tracking, we could look through
387  // extensions too.
388  if (BitsProvided < BitsRequired ||
389  (!AllowDifferingSizes && BitsProvided != BitsRequired))
390  return false;
391 
392  return true;
393 }
394 
395 /// For an aggregate type, determine whether a given index is within bounds or
396 /// not.
397 static bool indexReallyValid(CompositeType *T, unsigned Idx) {
398  if (ArrayType *AT = dyn_cast<ArrayType>(T))
399  return Idx < AT->getNumElements();
400 
401  return Idx < cast<StructType>(T)->getNumElements();
402 }
403 
404 /// Move the given iterators to the next leaf type in depth first traversal.
405 ///
406 /// Performs a depth-first traversal of the type as specified by its arguments,
407 /// stopping at the next leaf node (which may be a legitimate scalar type or an
408 /// empty struct or array).
409 ///
410 /// @param SubTypes List of the partial components making up the type from
411 /// outermost to innermost non-empty aggregate. The element currently
412 /// represented is SubTypes.back()->getTypeAtIndex(Path.back() - 1).
413 ///
414 /// @param Path Set of extractvalue indices leading from the outermost type
415 /// (SubTypes[0]) to the leaf node currently represented.
416 ///
417 /// @returns true if a new type was found, false otherwise. Calling this
418 /// function again on a finished iterator will repeatedly return
419 /// false. SubTypes.back()->getTypeAtIndex(Path.back()) is either an empty
420 /// aggregate or a non-aggregate
423  // First march back up the tree until we can successfully increment one of the
424  // coordinates in Path.
425  while (!Path.empty() && !indexReallyValid(SubTypes.back(), Path.back() + 1)) {
426  Path.pop_back();
427  SubTypes.pop_back();
428  }
429 
430  // If we reached the top, then the iterator is done.
431  if (Path.empty())
432  return false;
433 
434  // We know there's *some* valid leaf now, so march back down the tree picking
435  // out the left-most element at each node.
436  ++Path.back();
437  Type *DeeperType = SubTypes.back()->getTypeAtIndex(Path.back());
438  while (DeeperType->isAggregateType()) {
439  CompositeType *CT = cast<CompositeType>(DeeperType);
440  if (!indexReallyValid(CT, 0))
441  return true;
442 
443  SubTypes.push_back(CT);
444  Path.push_back(0);
445 
446  DeeperType = CT->getTypeAtIndex(0U);
447  }
448 
449  return true;
450 }
451 
452 /// Find the first non-empty, scalar-like type in Next and setup the iterator
453 /// components.
454 ///
455 /// Assuming Next is an aggregate of some kind, this function will traverse the
456 /// tree from left to right (i.e. depth-first) looking for the first
457 /// non-aggregate type which will play a role in function return.
458 ///
459 /// For example, if Next was {[0 x i64], {{}, i32, {}}, i32} then we would setup
460 /// Path as [1, 1] and SubTypes as [Next, {{}, i32, {}}] to represent the first
461 /// i32 in that type.
462 static bool firstRealType(Type *Next,
465  // First initialise the iterator components to the first "leaf" node
466  // (i.e. node with no valid sub-type at any index, so {} does count as a leaf
467  // despite nominally being an aggregate).
468  while (Next->isAggregateType() &&
469  indexReallyValid(cast<CompositeType>(Next), 0)) {
470  SubTypes.push_back(cast<CompositeType>(Next));
471  Path.push_back(0);
472  Next = cast<CompositeType>(Next)->getTypeAtIndex(0U);
473  }
474 
475  // If there's no Path now, Next was originally scalar already (or empty
476  // leaf). We're done.
477  if (Path.empty())
478  return true;
479 
480  // Otherwise, use normal iteration to keep looking through the tree until we
481  // find a non-aggregate type.
482  while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType()) {
483  if (!advanceToNextLeafType(SubTypes, Path))
484  return false;
485  }
486 
487  return true;
488 }
489 
490 /// Set the iterator data-structures to the next non-empty, non-aggregate
491 /// subtype.
494  do {
495  if (!advanceToNextLeafType(SubTypes, Path))
496  return false;
497 
498  assert(!Path.empty() && "found a leaf but didn't set the path?");
499  } while (SubTypes.back()->getTypeAtIndex(Path.back())->isAggregateType());
500 
501  return true;
502 }
503 
504 
505 /// Test if the given instruction is in a position to be optimized
506 /// with a tail-call. This roughly means that it's in a block with
507 /// a return and there's nothing that needs to be scheduled
508 /// between it and the return.
509 ///
510 /// This function only tests target-independent requirements.
512  const Instruction *I = CS.getInstruction();
513  const BasicBlock *ExitBB = I->getParent();
514  const Instruction *Term = ExitBB->getTerminator();
515  const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
516 
517  // The block must end in a return statement or unreachable.
518  //
519  // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
520  // an unreachable, for now. The way tailcall optimization is currently
521  // implemented means it will add an epilogue followed by a jump. That is
522  // not profitable. Also, if the callee is a special function (e.g.
523  // longjmp on x86), it can end up causing miscompilation that has not
524  // been fully understood.
525  if (!Ret &&
526  (!TM.Options.GuaranteedTailCallOpt || !isa<UnreachableInst>(Term)))
527  return false;
528 
529  // If I will have a chain, make sure no other instruction that will have a
530  // chain interposes between I and the return.
531  if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
533  for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) {
534  if (&*BBI == I)
535  break;
536  // Debug info intrinsics do not get in the way of tail call optimization.
537  if (isa<DbgInfoIntrinsic>(BBI))
538  continue;
539  // A lifetime end or assume intrinsic should not stop tail call
540  // optimization.
541  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
542  if (II->getIntrinsicID() == Intrinsic::lifetime_end ||
543  II->getIntrinsicID() == Intrinsic::assume)
544  continue;
545  if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
547  return false;
548  }
549 
550  const Function *F = ExitBB->getParent();
552  F, I, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering());
553 }
554 
556  const ReturnInst *Ret,
557  const TargetLoweringBase &TLI,
558  bool *AllowDifferingSizes) {
559  // ADS may be null, so don't write to it directly.
560  bool DummyADS;
561  bool &ADS = AllowDifferingSizes ? *AllowDifferingSizes : DummyADS;
562  ADS = true;
563 
565  AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
567 
568  // NoAlias and NonNull are completely benign as far as calling convention
569  // goes, they shouldn't affect whether the call is a tail call.
570  CallerAttrs.removeAttribute(Attribute::NoAlias);
571  CalleeAttrs.removeAttribute(Attribute::NoAlias);
572  CallerAttrs.removeAttribute(Attribute::NonNull);
573  CalleeAttrs.removeAttribute(Attribute::NonNull);
574 
575  if (CallerAttrs.contains(Attribute::ZExt)) {
576  if (!CalleeAttrs.contains(Attribute::ZExt))
577  return false;
578 
579  ADS = false;
580  CallerAttrs.removeAttribute(Attribute::ZExt);
581  CalleeAttrs.removeAttribute(Attribute::ZExt);
582  } else if (CallerAttrs.contains(Attribute::SExt)) {
583  if (!CalleeAttrs.contains(Attribute::SExt))
584  return false;
585 
586  ADS = false;
587  CallerAttrs.removeAttribute(Attribute::SExt);
588  CalleeAttrs.removeAttribute(Attribute::SExt);
589  }
590 
591  // Drop sext and zext return attributes if the result is not used.
592  // This enables tail calls for code like:
593  //
594  // define void @caller() {
595  // entry:
596  // %unused_result = tail call zeroext i1 @callee()
597  // br label %retlabel
598  // retlabel:
599  // ret void
600  // }
601  if (I->use_empty()) {
602  CalleeAttrs.removeAttribute(Attribute::SExt);
603  CalleeAttrs.removeAttribute(Attribute::ZExt);
604  }
605 
606  // If they're still different, there's some facet we don't understand
607  // (currently only "inreg", but in future who knows). It may be OK but the
608  // only safe option is to reject the tail call.
609  return CallerAttrs == CalleeAttrs;
610 }
611 
613  const Instruction *I,
614  const ReturnInst *Ret,
615  const TargetLoweringBase &TLI) {
616  // If the block ends with a void return or unreachable, it doesn't matter
617  // what the call's return type is.
618  if (!Ret || Ret->getNumOperands() == 0) return true;
619 
620  // If the return value is undef, it doesn't matter what the call's
621  // return type is.
622  if (isa<UndefValue>(Ret->getOperand(0))) return true;
623 
624  // Make sure the attributes attached to each return are compatible.
625  bool AllowDifferingSizes;
626  if (!attributesPermitTailCall(F, I, Ret, TLI, &AllowDifferingSizes))
627  return false;
628 
629  const Value *RetVal = Ret->getOperand(0), *CallVal = I;
630  // Intrinsic like llvm.memcpy has no return value, but the expanded
631  // libcall may or may not have return value. On most platforms, it
632  // will be expanded as memcpy in libc, which returns the first
633  // argument. On other platforms like arm-none-eabi, memcpy may be
634  // expanded as library call without return value, like __aeabi_memcpy.
635  const CallInst *Call = cast<CallInst>(I);
636  if (Function *F = Call->getCalledFunction()) {
637  Intrinsic::ID IID = F->getIntrinsicID();
638  if (((IID == Intrinsic::memcpy &&
639  TLI.getLibcallName(RTLIB::MEMCPY) == StringRef("memcpy")) ||
640  (IID == Intrinsic::memmove &&
641  TLI.getLibcallName(RTLIB::MEMMOVE) == StringRef("memmove")) ||
642  (IID == Intrinsic::memset &&
643  TLI.getLibcallName(RTLIB::MEMSET) == StringRef("memset"))) &&
644  RetVal == Call->getArgOperand(0))
645  return true;
646  }
647 
648  SmallVector<unsigned, 4> RetPath, CallPath;
649  SmallVector<CompositeType *, 4> RetSubTypes, CallSubTypes;
650 
651  bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath);
652  bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath);
653 
654  // Nothing's actually returned, it doesn't matter what the callee put there
655  // it's a valid tail call.
656  if (RetEmpty)
657  return true;
658 
659  // Iterate pairwise through each of the value types making up the tail call
660  // and the corresponding return. For each one we want to know whether it's
661  // essentially going directly from the tail call to the ret, via operations
662  // that end up not generating any code.
663  //
664  // We allow a certain amount of covariance here. For example it's permitted
665  // for the tail call to define more bits than the ret actually cares about
666  // (e.g. via a truncate).
667  do {
668  if (CallEmpty) {
669  // We've exhausted the values produced by the tail call instruction, the
670  // rest are essentially undef. The type doesn't really matter, but we need
671  // *something*.
672  Type *SlotType = RetSubTypes.back()->getTypeAtIndex(RetPath.back());
673  CallVal = UndefValue::get(SlotType);
674  }
675 
676  // The manipulations performed when we're looking through an insertvalue or
677  // an extractvalue would happen at the front of the RetPath list, so since
678  // we have to copy it anyway it's more efficient to create a reversed copy.
679  SmallVector<unsigned, 4> TmpRetPath(RetPath.rbegin(), RetPath.rend());
680  SmallVector<unsigned, 4> TmpCallPath(CallPath.rbegin(), CallPath.rend());
681 
682  // Finally, we can check whether the value produced by the tail call at this
683  // index is compatible with the value we return.
684  if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath,
685  AllowDifferingSizes, TLI,
686  F->getParent()->getDataLayout()))
687  return false;
688 
689  CallEmpty = !nextRealType(CallSubTypes, CallPath);
690  } while(nextRealType(RetSubTypes, RetPath));
691 
692  return true;
693 }
694 
696  DenseMap<const MachineBasicBlock *, int> &EHScopeMembership, int EHScope,
697  const MachineBasicBlock *MBB) {
699  while (!Worklist.empty()) {
700  const MachineBasicBlock *Visiting = Worklist.pop_back_val();
701  // Don't follow blocks which start new scopes.
702  if (Visiting->isEHPad() && Visiting != MBB)
703  continue;
704 
705  // Add this MBB to our scope.
706  auto P = EHScopeMembership.insert(std::make_pair(Visiting, EHScope));
707 
708  // Don't revisit blocks.
709  if (!P.second) {
710  assert(P.first->second == EHScope && "MBB is part of two scopes!");
711  continue;
712  }
713 
714  // Returns are boundaries where scope transfer can occur, don't follow
715  // successors.
716  if (Visiting->isEHScopeReturnBlock())
717  continue;
718 
719  for (const MachineBasicBlock *Succ : Visiting->successors())
720  Worklist.push_back(Succ);
721  }
722 }
723 
727 
728  // We don't have anything to do if there aren't any EH pads.
729  if (!MF.hasEHScopes())
730  return EHScopeMembership;
731 
732  int EntryBBNumber = MF.front().getNumber();
733  bool IsSEH = isAsynchronousEHPersonality(
735 
741  for (const MachineBasicBlock &MBB : MF) {
742  if (MBB.isEHScopeEntry()) {
743  EHScopeBlocks.push_back(&MBB);
744  } else if (IsSEH && MBB.isEHPad()) {
745  SEHCatchPads.push_back(&MBB);
746  } else if (MBB.pred_empty()) {
747  UnreachableBlocks.push_back(&MBB);
748  }
749 
750  MachineBasicBlock::const_iterator MBBI = MBB.getFirstTerminator();
751 
752  // CatchPads are not scopes for SEH so do not consider CatchRet to
753  // transfer control to another scope.
754  if (MBBI == MBB.end() || MBBI->getOpcode() != TII->getCatchReturnOpcode())
755  continue;
756 
757  // FIXME: SEH CatchPads are not necessarily in the parent function:
758  // they could be inside a finally block.
759  const MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB();
760  const MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB();
761  CatchRetSuccessors.push_back(
762  {Successor, IsSEH ? EntryBBNumber : SuccessorColor->getNumber()});
763  }
764 
765  // We don't have anything to do if there aren't any EH pads.
766  if (EHScopeBlocks.empty())
767  return EHScopeMembership;
768 
769  // Identify all the basic blocks reachable from the function entry.
770  collectEHScopeMembers(EHScopeMembership, EntryBBNumber, &MF.front());
771  // All blocks not part of a scope are in the parent function.
772  for (const MachineBasicBlock *MBB : UnreachableBlocks)
773  collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB);
774  // Next, identify all the blocks inside the scopes.
775  for (const MachineBasicBlock *MBB : EHScopeBlocks)
776  collectEHScopeMembers(EHScopeMembership, MBB->getNumber(), MBB);
777  // SEH CatchPads aren't really scopes, handle them separately.
778  for (const MachineBasicBlock *MBB : SEHCatchPads)
779  collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB);
780  // Finally, identify all the targets of a catchret.
781  for (std::pair<const MachineBasicBlock *, int> CatchRetPair :
782  CatchRetSuccessors)
783  collectEHScopeMembers(EHScopeMembership, CatchRetPair.second,
784  CatchRetPair.first);
785  return EHScopeMembership;
786 }
static unsigned getBitWidth(Type *Ty, const DataLayout &DL)
Returns the bitwidth of the given scalar or pointer type.
Return a value (possibly void), from a function.
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:111
ISD::CondCode getICmpCondCode(ICmpInst::Predicate Pred)
getICmpCondCode - Return the ISD condition code corresponding to the given LLVM IR integer condition ...
Definition: Analysis.cpp:238
This instruction extracts a struct member or array element value from an aggregate value...
bool isEHScopeReturnBlock() const
Convenience function that returns true if the bock ends in a EH scope return instruction.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
iterator begin() const
Definition: ArrayRef.h:136
const StructLayout * getStructLayout(StructType *Ty) const
Returns a StructLayout object, indicating the alignment of the struct, its size, and the offsets of i...
Definition: DataLayout.cpp:610
This class represents a function call, abstracting a target machine&#39;s calling convention.
virtual const TargetLowering * getTargetLowering() const
reverse_iterator rbegin() const
Definition: ArrayRef.h:139
unsigned less or equal
Definition: InstrTypes.h:758
static const Value * getNoopInput(const Value *V, SmallVectorImpl< unsigned > &ValLoc, unsigned &DataBits, const TargetLoweringBase &TLI, const DataLayout &DL)
Look through operations that will be free to find the earliest source of this value.
Definition: Analysis.cpp:273
The two locations do not alias at all.
Definition: AliasAnalysis.h:84
unsigned less than
Definition: InstrTypes.h:757
0 1 0 0 True if ordered and less than
Definition: InstrTypes.h:738
Offsets
Offsets in bytes from the start of the input buffer.
Definition: SIInstrInfo.h:1100
1 1 1 0 True if unordered or not equal
Definition: InstrTypes.h:748
unsigned getPointerSizeInBits(unsigned AS=0) const
Layout pointer size, in bits FIXME: The defaults need to be removed once all of the backends/clients ...
Definition: DataLayout.h:389
F(f)
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:137
GlobalValue * ExtractTypeInfo(Value *V)
ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
Definition: Analysis.cpp:158
bool returnTypeIsEligibleForTailCall(const Function *F, const Instruction *I, const ReturnInst *Ret, const TargetLoweringBase &TLI)
Test if given that the input instruction is in the tail call position if the return type or any attri...
Definition: Analysis.cpp:612
ConstraintCodeVector Codes
Code - The constraint code, either the register name (in braces) or the constraint letter/number...
Definition: InlineAsm.h:148
iterator_range< succ_iterator > successors()
Value * getArgOperand(unsigned i) const
Definition: InstrTypes.h:1241
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:221
1 0 0 1 True if unordered or equal
Definition: InstrTypes.h:743
Used to lazily calculate structure layout information for a target machine, based on the DataLayout s...
Definition: DataLayout.h:559
1 0 0 0 True if unordered: isnan(X) | isnan(Y)
Definition: InstrTypes.h:742
const DataLayout & getDataLayout() const
Get the data layout for the module&#39;s target platform.
Definition: Module.cpp:369
const HexagonInstrInfo * TII
Class to represent struct types.
Definition: DerivedTypes.h:233
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
0 1 0 1 True if ordered and less than or equal
Definition: InstrTypes.h:739
unsigned getCatchReturnOpcode() const
This class defines information used to lower LLVM code to legal SelectionDAG operators that the targe...
AttributeList getAttributes(LLVMContext &C, ID id)
Return the attributes for an intrinsic.
InstrTy * getInstruction() const
Definition: CallSite.h:96
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
Class to represent array types.
Definition: DerivedTypes.h:403
AttributeList getAttributes() const
Return the attribute list for this Function.
Definition: Function.h:223
CondCode
ISD::CondCode enum - These are ordered carefully to make the bitfields below work out...
Definition: ISDOpcodes.h:1012
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they&#39;re not in a MachineFuncti...
virtual const TargetInstrInfo * getInstrInfo() const
ISD::CondCode getFCmpCondCode(FCmpInst::Predicate Pred)
getFCmpCondCode - Return the ISD condition code corresponding to the given LLVM IR floating-point con...
Definition: Analysis.cpp:201
Type::subtype_iterator element_iterator
Definition: DerivedTypes.h:333
void ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL, Type *Ty, SmallVectorImpl< EVT > &ValueVTs, SmallVectorImpl< uint64_t > *Offsets=nullptr, uint64_t StartingOffset=0)
ComputeValueVTs - Given an LLVM IR type, compute a sequence of EVTs that represent all the individual...
Definition: Analysis.cpp:119
Value * getOperand(unsigned i) const
Definition: User.h:169
bool hasInlineAsmMemConstraint(InlineAsm::ConstraintInfoVector &CInfos, const TargetLowering &TLI)
hasInlineAsmMemConstraint - Return true if the inline asm instruction being processed uses a memory &#39;...
Definition: Analysis.cpp:179
TargetInstrInfo - Interface to description of machine instruction set.
bool isVoidTy() const
Return true if this is &#39;void&#39;.
Definition: Type.h:140
static bool indexReallyValid(CompositeType *T, unsigned Idx)
For an aggregate type, determine whether a given index is within bounds or not.
Definition: Analysis.cpp:397
static bool nextRealType(SmallVectorImpl< CompositeType *> &SubTypes, SmallVectorImpl< unsigned > &Path)
Set the iterator data-structures to the next non-empty, non-aggregate subtype.
Definition: Analysis.cpp:492
#define P(N)
LLVM Basic Block Representation.
Definition: BasicBlock.h:57
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
virtual ConstraintType getConstraintType(StringRef Constraint) const
Given a constraint, return the type of constraint it is for this target.
bool isIndirect
isIndirect - True if this operand is an indirect operand.
Definition: InlineAsm.h:144
size_t size() const
size - Get the array size.
Definition: ArrayRef.h:148
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
bool isPointerTy() const
True if this is an instance of PointerType.
Definition: Type.h:223
void computeValueLLTs(const DataLayout &DL, Type &Ty, SmallVectorImpl< LLT > &ValueTys, SmallVectorImpl< uint64_t > *Offsets=nullptr, uint64_t StartingOffset=0)
computeValueLLTs - Given an LLVM IR type, compute a sequence of LLTs that represent all the individua...
Definition: Analysis.cpp:127
bool mayHaveSideEffects() const
Return true if the instruction may have side effects.
Definition: Instruction.h:572
EHPersonality classifyEHPersonality(const Value *Pers)
See if the given exception handling personality function is one that we understand.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:732
unsigned GuaranteedTailCallOpt
GuaranteedTailCallOpt - This flag is enabled when -tailcallopt is specified on the commandline...
static bool firstRealType(Type *Next, SmallVectorImpl< CompositeType *> &SubTypes, SmallVectorImpl< unsigned > &Path)
Find the first non-empty, scalar-like type in Next and setup the iterator components.
Definition: Analysis.cpp:462
0 1 1 1 True if ordered (no nans)
Definition: InstrTypes.h:741
1 1 1 1 Always true (always folded)
Definition: InstrTypes.h:749
virtual bool allowTruncateForTailCall(Type *FromTy, Type *ToTy) const
Return true if a truncation from FromTy to ToTy is permitted when deciding whether a call is in tail ...
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1446
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:525
static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal, SmallVectorImpl< unsigned > &RetIndices, SmallVectorImpl< unsigned > &CallIndices, bool AllowDifferingSizes, const TargetLoweringBase &TLI, const DataLayout &DL)
Return true if this scalar return value only has bits discarded on its path from the "tail call" to t...
Definition: Analysis.cpp:353
const MachineBasicBlock & front() const
size_t size() const
Definition: SmallVector.h:52
1 1 0 1 True if unordered, less than, or equal
Definition: InstrTypes.h:747
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
EVT getValueType(const DataLayout &DL, Type *Ty, bool AllowUnknown=false) const
Return the EVT corresponding to this LLVM type.
bool isInTailCallPosition(ImmutableCallSite CS, const TargetMachine &TM)
Test if the given instruction is in a position to be optimized with a tail-call.
Definition: Analysis.cpp:511
signed greater than
Definition: InstrTypes.h:759
std::vector< ConstraintInfo > ConstraintInfoVector
Definition: InlineAsm.h:115
This base class for TargetLowering contains the SelectionDAG-independent parts that can be used from ...
LLT getLLTForType(Type &Ty, const DataLayout &DL)
Construct a low-level type based on an LLVM type.
0 0 1 0 True if ordered and greater than
Definition: InstrTypes.h:736
Iterator for intrusive lists based on ilist_node.
unsigned getNumOperands() const
Definition: User.h:191
static bool isNoopBitcast(Type *T1, Type *T2, const TargetLoweringBase &TLI)
Definition: Analysis.cpp:255
iterator end()
Definition: BasicBlock.h:270
1 1 0 0 True if unordered or less than
Definition: InstrTypes.h:746
Module.h This file contains the declarations for the Module class.
iterator end() const
Definition: ArrayRef.h:137
bool isAggregateType() const
Return true if the type is an aggregate type.
Definition: Type.h:257
signed less than
Definition: InstrTypes.h:761
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:374
DenseMap< const MachineBasicBlock *, int > getEHScopeMembership(const MachineFunction &MF)
Definition: Analysis.cpp:725
static bool advanceToNextLeafType(SmallVectorImpl< CompositeType *> &SubTypes, SmallVectorImpl< unsigned > &Path)
Move the given iterators to the next leaf type in depth first traversal.
Definition: Analysis.cpp:421
ISD::CondCode getFCmpCodeWithoutNaN(ISD::CondCode CC)
getFCmpCodeWithoutNaN - Given an ISD condition code comparing floats, return the equivalent code if w...
Definition: Analysis.cpp:223
Intrinsic::ID getIntrinsicID() const LLVM_READONLY
getIntrinsicID - This method returns the ID number of the specified function, or Intrinsic::not_intri...
Definition: Function.h:193
const Function & getFunction() const
Return the LLVM function that this machine code represents.
virtual const TargetSubtargetInfo * getSubtargetImpl(const Function &) const
Virtual method implemented by subclasses that returns a reference to that target&#39;s TargetSubtargetInf...
signed less or equal
Definition: InstrTypes.h:762
bool isTypeLegal(EVT VT) const
Return true if the target has native support for the specified value type.
void append(in_iter in_start, in_iter in_end)
Add the specified range to the end of the SmallVector.
Definition: SmallVector.h:387
Common super class of ArrayType, StructType and VectorType.
Definition: DerivedTypes.h:194
static void collectEHScopeMembers(DenseMap< const MachineBasicBlock *, int > &EHScopeMembership, int EHScope, const MachineBasicBlock *MBB)
Definition: Analysis.cpp:695
uint64_t getTypeAllocSize(Type *Ty) const
Returns the offset in bytes between successive objects of the specified type, including alignment pad...
Definition: DataLayout.h:470
reverse_iterator rend() const
Definition: ArrayRef.h:140
uint64_t getElementOffset(unsigned Idx) const
Definition: DataLayout.h:581
bool isEHPad() const
Returns true if the block is a landing pad.
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
unsigned greater or equal
Definition: InstrTypes.h:756
TargetOptions Options
Establish a view to a call site for examination.
Definition: CallSite.h:897
Function * getCalledFunction() const
Returns the function called, or null if this is an indirect function invocation.
Definition: InstrTypes.h:1287
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:106
#define I(x, y, z)
Definition: MD5.cpp:58
bool mayReadFromMemory() const
Return true if this instruction may read memory.
0 1 1 0 True if ordered and operands are unequal
Definition: InstrTypes.h:740
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:332
1 0 1 0 True if unordered or greater than
Definition: InstrTypes.h:744
static EVT getEVT(Type *Ty, bool HandleUnknown=false)
Return the value type corresponding to the specified type.
Definition: ValueTypes.cpp:473
EVT getMemValueType(const DataLayout &DL, Type *Ty, bool AllowUnknown=false) const
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
bool isAsynchronousEHPersonality(EHPersonality Pers)
Returns true if this personality function catches asynchronous exceptions.
bool isSafeToSpeculativelyExecute(const Value *V, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr)
Return true if the instruction does not have any effects besides calculating the result and does not ...
unsigned getPrimitiveSizeInBits() const LLVM_READONLY
Return the basic size of this type if it is a primitive type.
Definition: Type.cpp:114
0 0 0 1 True if ordered and equal
Definition: InstrTypes.h:735
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:575
LLVM Value Representation.
Definition: Value.h:73
Constant * getPersonalityFn() const
Get the personality function associated with this function.
Definition: Function.cpp:1384
1 0 1 1 True if unordered, greater than, or equal
Definition: InstrTypes.h:745
Primary interface to the complete machine description for the target machine.
Definition: TargetMachine.h:65
unsigned greater than
Definition: InstrTypes.h:755
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
bool attributesPermitTailCall(const Function *F, const Instruction *I, const ReturnInst *Ret, const TargetLoweringBase &TLI, bool *AllowDifferingSizes=nullptr)
Test if given that the input instruction is in the tail call position, if there is an attribute misma...
Definition: Analysis.cpp:555
0 0 1 1 True if ordered and greater than or equal
Definition: InstrTypes.h:737
unsigned ComputeLinearIndex(Type *Ty, const unsigned *Indices, const unsigned *IndicesEnd, unsigned CurIndex=0)
Compute the linearized index of a member in a nested aggregate/struct/array.
Definition: Analysis.cpp:35
bool use_empty() const
Definition: Value.h:342
#define T1
0 0 0 0 Always false (always folded)
Definition: InstrTypes.h:734
signed greater or equal
Definition: InstrTypes.h:760
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:43
This file describes how to lower LLVM code to machine code.
Type * getTypeAtIndex(const Value *V) const
Given an index value into the type, return the type of the element.
Definition: Type.cpp:531
const BasicBlock * getParent() const
Definition: Instruction.h:66
const char * getLibcallName(RTLIB::Libcall Call) const
Get the libcall routine name for the specified libcall.
This instruction inserts a struct field of array element value into an aggregate value.
void resize(size_type N)
Definition: SmallVector.h:344