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

source code of llvm/lib/CodeGen/Analysis.cpp