Bug Summary

File:llvm/lib/CodeGen/Analysis.cpp
Warning:line 178, column 14
Value stored to 'V' is never read

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name Analysis.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/lib/CodeGen -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/include -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/llvm/include -D NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/lib/CodeGen -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e=. -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2021-09-04-040900-46481-1 -x c++ /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/llvm/lib/CodeGen/Analysis.cpp
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/LLVMContext.h"
25#include "llvm/IR/Module.h"
26#include "llvm/Support/ErrorHandling.h"
27#include "llvm/Support/MathExtras.h"
28#include "llvm/Target/TargetMachine.h"
29#include "llvm/Transforms/Utils/GlobalStatus.h"
30
31using namespace llvm;
32
33/// Compute the linearized index of a member in a nested aggregate/struct/array
34/// by recursing and accumulating CurIndex as long as there are indices in the
35/// index list.
36unsigned llvm::ComputeLinearIndex(Type *Ty,
37 const unsigned *Indices,
38 const unsigned *IndicesEnd,
39 unsigned CurIndex) {
40 // Base case: We're done.
41 if (Indices && Indices == IndicesEnd)
42 return CurIndex;
43
44 // Given a struct type, recursively traverse the elements.
45 if (StructType *STy = dyn_cast<StructType>(Ty)) {
46 for (auto I : llvm::enumerate(STy->elements())) {
47 Type *ET = I.value();
48 if (Indices && *Indices == I.index())
49 return ComputeLinearIndex(ET, Indices + 1, IndicesEnd, CurIndex);
50 CurIndex = ComputeLinearIndex(ET, nullptr, nullptr, CurIndex);
51 }
52 assert(!Indices && "Unexpected out of bound")(static_cast<void> (0));
53 return CurIndex;
54 }
55 // Given an array type, recursively traverse the elements.
56 else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
57 Type *EltTy = ATy->getElementType();
58 unsigned NumElts = ATy->getNumElements();
59 // Compute the Linear offset when jumping one element of the array
60 unsigned EltLinearOffset = ComputeLinearIndex(EltTy, nullptr, nullptr, 0);
61 if (Indices) {
62 assert(*Indices < NumElts && "Unexpected out of bound")(static_cast<void> (0));
63 // If the indice is inside the array, compute the index to the requested
64 // elt and recurse inside the element with the end of the indices list
65 CurIndex += EltLinearOffset* *Indices;
66 return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
67 }
68 CurIndex += EltLinearOffset*NumElts;
69 return CurIndex;
70 }
71 // We haven't found the type we're looking for, so keep searching.
72 return CurIndex + 1;
73}
74
75/// ComputeValueVTs - Given an LLVM IR type, compute a sequence of
76/// EVTs that represent all the individual underlying
77/// non-aggregate types that comprise it.
78///
79/// If Offsets is non-null, it points to a vector to be filled in
80/// with the in-memory offsets of each of the individual values.
81///
82void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
83 Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
84 SmallVectorImpl<EVT> *MemVTs,
85 SmallVectorImpl<uint64_t> *Offsets,
86 uint64_t StartingOffset) {
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 uint64_t EltOffset = SL ? SL->getElementOffset(EI - EB) : 0;
99 ComputeValueVTs(TLI, DL, *EI, ValueVTs, MemVTs, Offsets,
100 StartingOffset + EltOffset);
101 }
102 return;
103 }
104 // Given an array type, recursively traverse the elements.
105 if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
106 Type *EltTy = ATy->getElementType();
107 uint64_t EltSize = DL.getTypeAllocSize(EltTy).getFixedValue();
108 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
109 ComputeValueVTs(TLI, DL, EltTy, ValueVTs, MemVTs, Offsets,
110 StartingOffset + i * EltSize);
111 return;
112 }
113 // Interpret void as zero return values.
114 if (Ty->isVoidTy())
115 return;
116 // Base case: we can get an EVT for this LLVM IR type.
117 ValueVTs.push_back(TLI.getValueType(DL, Ty));
118 if (MemVTs)
119 MemVTs->push_back(TLI.getMemValueType(DL, Ty));
120 if (Offsets)
121 Offsets->push_back(StartingOffset);
122}
123
124void llvm::ComputeValueVTs(const TargetLowering &TLI, const DataLayout &DL,
125 Type *Ty, SmallVectorImpl<EVT> &ValueVTs,
126 SmallVectorImpl<uint64_t> *Offsets,
127 uint64_t StartingOffset) {
128 return ComputeValueVTs(TLI, DL, Ty, ValueVTs, /*MemVTs=*/nullptr, Offsets,
129 StartingOffset);
130}
131
132void llvm::computeValueLLTs(const DataLayout &DL, Type &Ty,
133 SmallVectorImpl<LLT> &ValueTys,
134 SmallVectorImpl<uint64_t> *Offsets,
135 uint64_t StartingOffset) {
136 // Given a struct type, recursively traverse the elements.
137 if (StructType *STy = dyn_cast<StructType>(&Ty)) {
138 // If the Offsets aren't needed, don't query the struct layout. This allows
139 // us to support structs with scalable vectors for operations that don't
140 // need offsets.
141 const StructLayout *SL = Offsets ? DL.getStructLayout(STy) : nullptr;
142 for (unsigned I = 0, E = STy->getNumElements(); I != E; ++I) {
143 uint64_t EltOffset = SL ? SL->getElementOffset(I) : 0;
144 computeValueLLTs(DL, *STy->getElementType(I), ValueTys, Offsets,
145 StartingOffset + EltOffset);
146 }
147 return;
148 }
149 // Given an array type, recursively traverse the elements.
150 if (ArrayType *ATy = dyn_cast<ArrayType>(&Ty)) {
151 Type *EltTy = ATy->getElementType();
152 uint64_t EltSize = DL.getTypeAllocSize(EltTy).getFixedValue();
153 for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
154 computeValueLLTs(DL, *EltTy, ValueTys, Offsets,
155 StartingOffset + i * EltSize);
156 return;
157 }
158 // Interpret void as zero return values.
159 if (Ty.isVoidTy())
160 return;
161 // Base case: we can get an LLT for this LLVM IR type.
162 ValueTys.push_back(getLLTForType(Ty, DL));
163 if (Offsets != nullptr)
164 Offsets->push_back(StartingOffset * 8);
165}
166
167/// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
168GlobalValue *llvm::ExtractTypeInfo(Value *V) {
169 V = V->stripPointerCasts();
170 GlobalValue *GV = dyn_cast<GlobalValue>(V);
171 GlobalVariable *Var = dyn_cast<GlobalVariable>(V);
172
173 if (Var && Var->getName() == "llvm.eh.catch.all.value") {
174 assert(Var->hasInitializer() &&(static_cast<void> (0))
175 "The EH catch-all value must have an initializer")(static_cast<void> (0));
176 Value *Init = Var->getInitializer();
177 GV = dyn_cast<GlobalValue>(Init);
178 if (!GV) V = cast<ConstantPointerNull>(Init);
Value stored to 'V' is never read
179 }
180
181 assert((GV || isa<ConstantPointerNull>(V)) &&(static_cast<void> (0))
182 "TypeInfo must be a global variable or NULL")(static_cast<void> (0));
183 return GV;
184}
185
186/// getFCmpCondCode - Return the ISD condition code corresponding to
187/// the given LLVM IR floating-point condition code. This includes
188/// consideration of global floating-point math flags.
189///
190ISD::CondCode llvm::getFCmpCondCode(FCmpInst::Predicate Pred) {
191 switch (Pred) {
192 case FCmpInst::FCMP_FALSE: return ISD::SETFALSE;
193 case FCmpInst::FCMP_OEQ: return ISD::SETOEQ;
194 case FCmpInst::FCMP_OGT: return ISD::SETOGT;
195 case FCmpInst::FCMP_OGE: return ISD::SETOGE;
196 case FCmpInst::FCMP_OLT: return ISD::SETOLT;
197 case FCmpInst::FCMP_OLE: return ISD::SETOLE;
198 case FCmpInst::FCMP_ONE: return ISD::SETONE;
199 case FCmpInst::FCMP_ORD: return ISD::SETO;
200 case FCmpInst::FCMP_UNO: return ISD::SETUO;
201 case FCmpInst::FCMP_UEQ: return ISD::SETUEQ;
202 case FCmpInst::FCMP_UGT: return ISD::SETUGT;
203 case FCmpInst::FCMP_UGE: return ISD::SETUGE;
204 case FCmpInst::FCMP_ULT: return ISD::SETULT;
205 case FCmpInst::FCMP_ULE: return ISD::SETULE;
206 case FCmpInst::FCMP_UNE: return ISD::SETUNE;
207 case FCmpInst::FCMP_TRUE: return ISD::SETTRUE;
208 default: llvm_unreachable("Invalid FCmp predicate opcode!")__builtin_unreachable();
209 }
210}
211
212ISD::CondCode llvm::getFCmpCodeWithoutNaN(ISD::CondCode CC) {
213 switch (CC) {
214 case ISD::SETOEQ: case ISD::SETUEQ: return ISD::SETEQ;
215 case ISD::SETONE: case ISD::SETUNE: return ISD::SETNE;
216 case ISD::SETOLT: case ISD::SETULT: return ISD::SETLT;
217 case ISD::SETOLE: case ISD::SETULE: return ISD::SETLE;
218 case ISD::SETOGT: case ISD::SETUGT: return ISD::SETGT;
219 case ISD::SETOGE: case ISD::SETUGE: return ISD::SETGE;
220 default: return CC;
221 }
222}
223
224/// getICmpCondCode - Return the ISD condition code corresponding to
225/// the given LLVM IR integer condition code.
226///
227ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
228 switch (Pred) {
229 case ICmpInst::ICMP_EQ: return ISD::SETEQ;
230 case ICmpInst::ICMP_NE: return ISD::SETNE;
231 case ICmpInst::ICMP_SLE: return ISD::SETLE;
232 case ICmpInst::ICMP_ULE: return ISD::SETULE;
233 case ICmpInst::ICMP_SGE: return ISD::SETGE;
234 case ICmpInst::ICMP_UGE: return ISD::SETUGE;
235 case ICmpInst::ICMP_SLT: return ISD::SETLT;
236 case ICmpInst::ICMP_ULT: return ISD::SETULT;
237 case ICmpInst::ICMP_SGT: return ISD::SETGT;
238 case ICmpInst::ICMP_UGT: return ISD::SETUGT;
239 default:
240 llvm_unreachable("Invalid ICmp predicate opcode!")__builtin_unreachable();
241 }
242}
243
244static bool isNoopBitcast(Type *T1, Type *T2,
245 const TargetLoweringBase& TLI) {
246 return T1 == T2 || (T1->isPointerTy() && T2->isPointerTy()) ||
247 (isa<VectorType>(T1) && isa<VectorType>(T2) &&
248 TLI.isTypeLegal(EVT::getEVT(T1)) && TLI.isTypeLegal(EVT::getEVT(T2)));
249}
250
251/// Look through operations that will be free to find the earliest source of
252/// this value.
253///
254/// @param ValLoc If V has aggregate type, we will be interested in a particular
255/// scalar component. This records its address; the reverse of this list gives a
256/// sequence of indices appropriate for an extractvalue to locate the important
257/// value. This value is updated during the function and on exit will indicate
258/// similar information for the Value returned.
259///
260/// @param DataBits If this function looks through truncate instructions, this
261/// will record the smallest size attained.
262static const Value *getNoopInput(const Value *V,
263 SmallVectorImpl<unsigned> &ValLoc,
264 unsigned &DataBits,
265 const TargetLoweringBase &TLI,
266 const DataLayout &DL) {
267 while (true) {
268 // Try to look through V1; if V1 is not an instruction, it can't be looked
269 // through.
270 const Instruction *I = dyn_cast<Instruction>(V);
271 if (!I || I->getNumOperands() == 0) return V;
272 const Value *NoopInput = nullptr;
273
274 Value *Op = I->getOperand(0);
275 if (isa<BitCastInst>(I)) {
276 // Look through truly no-op bitcasts.
277 if (isNoopBitcast(Op->getType(), I->getType(), TLI))
278 NoopInput = Op;
279 } else if (isa<GetElementPtrInst>(I)) {
280 // Look through getelementptr
281 if (cast<GetElementPtrInst>(I)->hasAllZeroIndices())
282 NoopInput = Op;
283 } else if (isa<IntToPtrInst>(I)) {
284 // Look through inttoptr.
285 // Make sure this isn't a truncating or extending cast. We could
286 // support this eventually, but don't bother for now.
287 if (!isa<VectorType>(I->getType()) &&
288 DL.getPointerSizeInBits() ==
289 cast<IntegerType>(Op->getType())->getBitWidth())
290 NoopInput = Op;
291 } else if (isa<PtrToIntInst>(I)) {
292 // Look through ptrtoint.
293 // Make sure this isn't a truncating or extending cast. We could
294 // support this eventually, but don't bother for now.
295 if (!isa<VectorType>(I->getType()) &&
296 DL.getPointerSizeInBits() ==
297 cast<IntegerType>(I->getType())->getBitWidth())
298 NoopInput = Op;
299 } else if (isa<TruncInst>(I) &&
300 TLI.allowTruncateForTailCall(Op->getType(), I->getType())) {
301 DataBits = std::min((uint64_t)DataBits,
302 I->getType()->getPrimitiveSizeInBits().getFixedSize());
303 NoopInput = Op;
304 } else if (auto *CB = dyn_cast<CallBase>(I)) {
305 const Value *ReturnedOp = CB->getReturnedArgOperand();
306 if (ReturnedOp && isNoopBitcast(ReturnedOp->getType(), I->getType(), TLI))
307 NoopInput = ReturnedOp;
308 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(V)) {
309 // Value may come from either the aggregate or the scalar
310 ArrayRef<unsigned> InsertLoc = IVI->getIndices();
311 if (ValLoc.size() >= InsertLoc.size() &&
312 std::equal(InsertLoc.begin(), InsertLoc.end(), ValLoc.rbegin())) {
313 // The type being inserted is a nested sub-type of the aggregate; we
314 // have to remove those initial indices to get the location we're
315 // interested in for the operand.
316 ValLoc.resize(ValLoc.size() - InsertLoc.size());
317 NoopInput = IVI->getInsertedValueOperand();
318 } else {
319 // The struct we're inserting into has the value we're interested in, no
320 // change of address.
321 NoopInput = Op;
322 }
323 } else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
324 // The part we're interested in will inevitably be some sub-section of the
325 // previous aggregate. Combine the two paths to obtain the true address of
326 // our element.
327 ArrayRef<unsigned> ExtractLoc = EVI->getIndices();
328 ValLoc.append(ExtractLoc.rbegin(), ExtractLoc.rend());
329 NoopInput = Op;
330 }
331 // Terminate if we couldn't find anything to look through.
332 if (!NoopInput)
333 return V;
334
335 V = NoopInput;
336 }
337}
338
339/// Return true if this scalar return value only has bits discarded on its path
340/// from the "tail call" to the "ret". This includes the obvious noop
341/// instructions handled by getNoopInput above as well as free truncations (or
342/// extensions prior to the call).
343static bool slotOnlyDiscardsData(const Value *RetVal, const Value *CallVal,
344 SmallVectorImpl<unsigned> &RetIndices,
345 SmallVectorImpl<unsigned> &CallIndices,
346 bool AllowDifferingSizes,
347 const TargetLoweringBase &TLI,
348 const DataLayout &DL) {
349
350 // Trace the sub-value needed by the return value as far back up the graph as
351 // possible, in the hope that it will intersect with the value produced by the
352 // call. In the simple case with no "returned" attribute, the hope is actually
353 // that we end up back at the tail call instruction itself.
354 unsigned BitsRequired = UINT_MAX(2147483647 *2U +1U);
355 RetVal = getNoopInput(RetVal, RetIndices, BitsRequired, TLI, DL);
356
357 // If this slot in the value returned is undef, it doesn't matter what the
358 // call puts there, it'll be fine.
359 if (isa<UndefValue>(RetVal))
360 return true;
361
362 // Now do a similar search up through the graph to find where the value
363 // actually returned by the "tail call" comes from. In the simple case without
364 // a "returned" attribute, the search will be blocked immediately and the loop
365 // a Noop.
366 unsigned BitsProvided = UINT_MAX(2147483647 *2U +1U);
367 CallVal = getNoopInput(CallVal, CallIndices, BitsProvided, TLI, DL);
368
369 // There's no hope if we can't actually trace them to (the same part of!) the
370 // same value.
371 if (CallVal != RetVal || CallIndices != RetIndices)
372 return false;
373
374 // However, intervening truncates may have made the call non-tail. Make sure
375 // all the bits that are needed by the "ret" have been provided by the "tail
376 // call". FIXME: with sufficiently cunning bit-tracking, we could look through
377 // extensions too.
378 if (BitsProvided < BitsRequired ||
379 (!AllowDifferingSizes && BitsProvided != BitsRequired))
380 return false;
381
382 return true;
383}
384
385/// For an aggregate type, determine whether a given index is within bounds or
386/// not.
387static bool indexReallyValid(Type *T, unsigned Idx) {
388 if (ArrayType *AT = dyn_cast<ArrayType>(T))
389 return Idx < AT->getNumElements();
390
391 return Idx < cast<StructType>(T)->getNumElements();
392}
393
394/// Move the given iterators to the next leaf type in depth first traversal.
395///
396/// Performs a depth-first traversal of the type as specified by its arguments,
397/// stopping at the next leaf node (which may be a legitimate scalar type or an
398/// empty struct or array).
399///
400/// @param SubTypes List of the partial components making up the type from
401/// outermost to innermost non-empty aggregate. The element currently
402/// represented is SubTypes.back()->getTypeAtIndex(Path.back() - 1).
403///
404/// @param Path Set of extractvalue indices leading from the outermost type
405/// (SubTypes[0]) to the leaf node currently represented.
406///
407/// @returns true if a new type was found, false otherwise. Calling this
408/// function again on a finished iterator will repeatedly return
409/// false. SubTypes.back()->getTypeAtIndex(Path.back()) is either an empty
410/// aggregate or a non-aggregate
411static bool advanceToNextLeafType(SmallVectorImpl<Type *> &SubTypes,
412 SmallVectorImpl<unsigned> &Path) {
413 // First march back up the tree until we can successfully increment one of the
414 // coordinates in Path.
415 while (!Path.empty() && !indexReallyValid(SubTypes.back(), Path.back() + 1)) {
416 Path.pop_back();
417 SubTypes.pop_back();
418 }
419
420 // If we reached the top, then the iterator is done.
421 if (Path.empty())
422 return false;
423
424 // We know there's *some* valid leaf now, so march back down the tree picking
425 // out the left-most element at each node.
426 ++Path.back();
427 Type *DeeperType =
428 ExtractValueInst::getIndexedType(SubTypes.back(), Path.back());
429 while (DeeperType->isAggregateType()) {
430 if (!indexReallyValid(DeeperType, 0))
431 return true;
432
433 SubTypes.push_back(DeeperType);
434 Path.push_back(0);
435
436 DeeperType = ExtractValueInst::getIndexedType(DeeperType, 0);
437 }
438
439 return true;
440}
441
442/// Find the first non-empty, scalar-like type in Next and setup the iterator
443/// components.
444///
445/// Assuming Next is an aggregate of some kind, this function will traverse the
446/// tree from left to right (i.e. depth-first) looking for the first
447/// non-aggregate type which will play a role in function return.
448///
449/// For example, if Next was {[0 x i64], {{}, i32, {}}, i32} then we would setup
450/// Path as [1, 1] and SubTypes as [Next, {{}, i32, {}}] to represent the first
451/// i32 in that type.
452static bool firstRealType(Type *Next, SmallVectorImpl<Type *> &SubTypes,
453 SmallVectorImpl<unsigned> &Path) {
454 // First initialise the iterator components to the first "leaf" node
455 // (i.e. node with no valid sub-type at any index, so {} does count as a leaf
456 // despite nominally being an aggregate).
457 while (Type *FirstInner = ExtractValueInst::getIndexedType(Next, 0)) {
458 SubTypes.push_back(Next);
459 Path.push_back(0);
460 Next = FirstInner;
461 }
462
463 // If there's no Path now, Next was originally scalar already (or empty
464 // leaf). We're done.
465 if (Path.empty())
466 return true;
467
468 // Otherwise, use normal iteration to keep looking through the tree until we
469 // find a non-aggregate type.
470 while (ExtractValueInst::getIndexedType(SubTypes.back(), Path.back())
471 ->isAggregateType()) {
472 if (!advanceToNextLeafType(SubTypes, Path))
473 return false;
474 }
475
476 return true;
477}
478
479/// Set the iterator data-structures to the next non-empty, non-aggregate
480/// subtype.
481static bool nextRealType(SmallVectorImpl<Type *> &SubTypes,
482 SmallVectorImpl<unsigned> &Path) {
483 do {
484 if (!advanceToNextLeafType(SubTypes, Path))
485 return false;
486
487 assert(!Path.empty() && "found a leaf but didn't set the path?")(static_cast<void> (0));
488 } while (ExtractValueInst::getIndexedType(SubTypes.back(), Path.back())
489 ->isAggregateType());
490
491 return true;
492}
493
494
495/// Test if the given instruction is in a position to be optimized
496/// with a tail-call. This roughly means that it's in a block with
497/// a return and there's nothing that needs to be scheduled
498/// between it and the return.
499///
500/// This function only tests target-independent requirements.
501bool llvm::isInTailCallPosition(const CallBase &Call, const TargetMachine &TM) {
502 const BasicBlock *ExitBB = Call.getParent();
503 const Instruction *Term = ExitBB->getTerminator();
504 const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
505
506 // The block must end in a return statement or unreachable.
507 //
508 // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
509 // an unreachable, for now. The way tailcall optimization is currently
510 // implemented means it will add an epilogue followed by a jump. That is
511 // not profitable. Also, if the callee is a special function (e.g.
512 // longjmp on x86), it can end up causing miscompilation that has not
513 // been fully understood.
514 if (!Ret && ((!TM.Options.GuaranteedTailCallOpt &&
515 Call.getCallingConv() != CallingConv::Tail &&
516 Call.getCallingConv() != CallingConv::SwiftTail) ||
517 !isa<UnreachableInst>(Term)))
518 return false;
519
520 // If I will have a chain, make sure no other instruction that will have a
521 // chain interposes between I and the return.
522 // Check for all calls including speculatable functions.
523 for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) {
524 if (&*BBI == &Call)
525 break;
526 // Debug info intrinsics do not get in the way of tail call optimization.
527 if (isa<DbgInfoIntrinsic>(BBI))
528 continue;
529 // Pseudo probe intrinsics do not block tail call optimization either.
530 if (isa<PseudoProbeInst>(BBI))
531 continue;
532 // A lifetime end, assume or noalias.decl intrinsic should not stop tail
533 // call optimization.
534 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
535 if (II->getIntrinsicID() == Intrinsic::lifetime_end ||
536 II->getIntrinsicID() == Intrinsic::assume ||
537 II->getIntrinsicID() == Intrinsic::experimental_noalias_scope_decl)
538 continue;
539 if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
540 !isSafeToSpeculativelyExecute(&*BBI))
541 return false;
542 }
543
544 const Function *F = ExitBB->getParent();
545 return returnTypeIsEligibleForTailCall(
546 F, &Call, Ret, *TM.getSubtargetImpl(*F)->getTargetLowering());
547}
548
549bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I,
550 const ReturnInst *Ret,
551 const TargetLoweringBase &TLI,
552 bool *AllowDifferingSizes) {
553 // ADS may be null, so don't write to it directly.
554 bool DummyADS;
555 bool &ADS = AllowDifferingSizes ? *AllowDifferingSizes : DummyADS;
556 ADS = true;
557
558 AttrBuilder CallerAttrs(F->getAttributes(), AttributeList::ReturnIndex);
559 AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
560 AttributeList::ReturnIndex);
561
562 // Following attributes are completely benign as far as calling convention
563 // goes, they shouldn't affect whether the call is a tail call.
564 for (const auto &Attr : {Attribute::Alignment, Attribute::Dereferenceable,
565 Attribute::DereferenceableOrNull, Attribute::NoAlias,
566 Attribute::NonNull}) {
567 CallerAttrs.removeAttribute(Attr);
568 CalleeAttrs.removeAttribute(Attr);
569 }
570
571 if (CallerAttrs.contains(Attribute::ZExt)) {
572 if (!CalleeAttrs.contains(Attribute::ZExt))
573 return false;
574
575 ADS = false;
576 CallerAttrs.removeAttribute(Attribute::ZExt);
577 CalleeAttrs.removeAttribute(Attribute::ZExt);
578 } else if (CallerAttrs.contains(Attribute::SExt)) {
579 if (!CalleeAttrs.contains(Attribute::SExt))
580 return false;
581
582 ADS = false;
583 CallerAttrs.removeAttribute(Attribute::SExt);
584 CalleeAttrs.removeAttribute(Attribute::SExt);
585 }
586
587 // Drop sext and zext return attributes if the result is not used.
588 // This enables tail calls for code like:
589 //
590 // define void @caller() {
591 // entry:
592 // %unused_result = tail call zeroext i1 @callee()
593 // br label %retlabel
594 // retlabel:
595 // ret void
596 // }
597 if (I->use_empty()) {
598 CalleeAttrs.removeAttribute(Attribute::SExt);
599 CalleeAttrs.removeAttribute(Attribute::ZExt);
600 }
601
602 // If they're still different, there's some facet we don't understand
603 // (currently only "inreg", but in future who knows). It may be OK but the
604 // only safe option is to reject the tail call.
605 return CallerAttrs == CalleeAttrs;
606}
607
608/// Check whether B is a bitcast of a pointer type to another pointer type,
609/// which is equal to A.
610static bool isPointerBitcastEqualTo(const Value *A, const Value *B) {
611 assert(A && B && "Expected non-null inputs!")(static_cast<void> (0));
612
613 auto *BitCastIn = dyn_cast<BitCastInst>(B);
614
615 if (!BitCastIn)
616 return false;
617
618 if (!A->getType()->isPointerTy() || !B->getType()->isPointerTy())
619 return false;
620
621 return A == BitCastIn->getOperand(0);
622}
623
624bool llvm::returnTypeIsEligibleForTailCall(const Function *F,
625 const Instruction *I,
626 const ReturnInst *Ret,
627 const TargetLoweringBase &TLI) {
628 // If the block ends with a void return or unreachable, it doesn't matter
629 // what the call's return type is.
630 if (!Ret || Ret->getNumOperands() == 0) return true;
631
632 // If the return value is undef, it doesn't matter what the call's
633 // return type is.
634 if (isa<UndefValue>(Ret->getOperand(0))) return true;
635
636 // Make sure the attributes attached to each return are compatible.
637 bool AllowDifferingSizes;
638 if (!attributesPermitTailCall(F, I, Ret, TLI, &AllowDifferingSizes))
639 return false;
640
641 const Value *RetVal = Ret->getOperand(0), *CallVal = I;
642 // Intrinsic like llvm.memcpy has no return value, but the expanded
643 // libcall may or may not have return value. On most platforms, it
644 // will be expanded as memcpy in libc, which returns the first
645 // argument. On other platforms like arm-none-eabi, memcpy may be
646 // expanded as library call without return value, like __aeabi_memcpy.
647 const CallInst *Call = cast<CallInst>(I);
648 if (Function *F = Call->getCalledFunction()) {
649 Intrinsic::ID IID = F->getIntrinsicID();
650 if (((IID == Intrinsic::memcpy &&
651 TLI.getLibcallName(RTLIB::MEMCPY) == StringRef("memcpy")) ||
652 (IID == Intrinsic::memmove &&
653 TLI.getLibcallName(RTLIB::MEMMOVE) == StringRef("memmove")) ||
654 (IID == Intrinsic::memset &&
655 TLI.getLibcallName(RTLIB::MEMSET) == StringRef("memset"))) &&
656 (RetVal == Call->getArgOperand(0) ||
657 isPointerBitcastEqualTo(RetVal, Call->getArgOperand(0))))
658 return true;
659 }
660
661 SmallVector<unsigned, 4> RetPath, CallPath;
662 SmallVector<Type *, 4> RetSubTypes, CallSubTypes;
663
664 bool RetEmpty = !firstRealType(RetVal->getType(), RetSubTypes, RetPath);
665 bool CallEmpty = !firstRealType(CallVal->getType(), CallSubTypes, CallPath);
666
667 // Nothing's actually returned, it doesn't matter what the callee put there
668 // it's a valid tail call.
669 if (RetEmpty)
670 return true;
671
672 // Iterate pairwise through each of the value types making up the tail call
673 // and the corresponding return. For each one we want to know whether it's
674 // essentially going directly from the tail call to the ret, via operations
675 // that end up not generating any code.
676 //
677 // We allow a certain amount of covariance here. For example it's permitted
678 // for the tail call to define more bits than the ret actually cares about
679 // (e.g. via a truncate).
680 do {
681 if (CallEmpty) {
682 // We've exhausted the values produced by the tail call instruction, the
683 // rest are essentially undef. The type doesn't really matter, but we need
684 // *something*.
685 Type *SlotType =
686 ExtractValueInst::getIndexedType(RetSubTypes.back(), RetPath.back());
687 CallVal = UndefValue::get(SlotType);
688 }
689
690 // The manipulations performed when we're looking through an insertvalue or
691 // an extractvalue would happen at the front of the RetPath list, so since
692 // we have to copy it anyway it's more efficient to create a reversed copy.
693 SmallVector<unsigned, 4> TmpRetPath(RetPath.rbegin(), RetPath.rend());
694 SmallVector<unsigned, 4> TmpCallPath(CallPath.rbegin(), CallPath.rend());
695
696 // Finally, we can check whether the value produced by the tail call at this
697 // index is compatible with the value we return.
698 if (!slotOnlyDiscardsData(RetVal, CallVal, TmpRetPath, TmpCallPath,
699 AllowDifferingSizes, TLI,
700 F->getParent()->getDataLayout()))
701 return false;
702
703 CallEmpty = !nextRealType(CallSubTypes, CallPath);
704 } while(nextRealType(RetSubTypes, RetPath));
705
706 return true;
707}
708
709static void collectEHScopeMembers(
710 DenseMap<const MachineBasicBlock *, int> &EHScopeMembership, int EHScope,
711 const MachineBasicBlock *MBB) {
712 SmallVector<const MachineBasicBlock *, 16> Worklist = {MBB};
713 while (!Worklist.empty()) {
714 const MachineBasicBlock *Visiting = Worklist.pop_back_val();
715 // Don't follow blocks which start new scopes.
716 if (Visiting->isEHPad() && Visiting != MBB)
717 continue;
718
719 // Add this MBB to our scope.
720 auto P = EHScopeMembership.insert(std::make_pair(Visiting, EHScope));
721
722 // Don't revisit blocks.
723 if (!P.second) {
724 assert(P.first->second == EHScope && "MBB is part of two scopes!")(static_cast<void> (0));
725 continue;
726 }
727
728 // Returns are boundaries where scope transfer can occur, don't follow
729 // successors.
730 if (Visiting->isEHScopeReturnBlock())
731 continue;
732
733 append_range(Worklist, Visiting->successors());
734 }
735}
736
737DenseMap<const MachineBasicBlock *, int>
738llvm::getEHScopeMembership(const MachineFunction &MF) {
739 DenseMap<const MachineBasicBlock *, int> EHScopeMembership;
740
741 // We don't have anything to do if there aren't any EH pads.
742 if (!MF.hasEHScopes())
743 return EHScopeMembership;
744
745 int EntryBBNumber = MF.front().getNumber();
746 bool IsSEH = isAsynchronousEHPersonality(
747 classifyEHPersonality(MF.getFunction().getPersonalityFn()));
748
749 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
750 SmallVector<const MachineBasicBlock *, 16> EHScopeBlocks;
751 SmallVector<const MachineBasicBlock *, 16> UnreachableBlocks;
752 SmallVector<const MachineBasicBlock *, 16> SEHCatchPads;
753 SmallVector<std::pair<const MachineBasicBlock *, int>, 16> CatchRetSuccessors;
754 for (const MachineBasicBlock &MBB : MF) {
755 if (MBB.isEHScopeEntry()) {
756 EHScopeBlocks.push_back(&MBB);
757 } else if (IsSEH && MBB.isEHPad()) {
758 SEHCatchPads.push_back(&MBB);
759 } else if (MBB.pred_empty()) {
760 UnreachableBlocks.push_back(&MBB);
761 }
762
763 MachineBasicBlock::const_iterator MBBI = MBB.getFirstTerminator();
764
765 // CatchPads are not scopes for SEH so do not consider CatchRet to
766 // transfer control to another scope.
767 if (MBBI == MBB.end() || MBBI->getOpcode() != TII->getCatchReturnOpcode())
768 continue;
769
770 // FIXME: SEH CatchPads are not necessarily in the parent function:
771 // they could be inside a finally block.
772 const MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB();
773 const MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB();
774 CatchRetSuccessors.push_back(
775 {Successor, IsSEH ? EntryBBNumber : SuccessorColor->getNumber()});
776 }
777
778 // We don't have anything to do if there aren't any EH pads.
779 if (EHScopeBlocks.empty())
780 return EHScopeMembership;
781
782 // Identify all the basic blocks reachable from the function entry.
783 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, &MF.front());
784 // All blocks not part of a scope are in the parent function.
785 for (const MachineBasicBlock *MBB : UnreachableBlocks)
786 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB);
787 // Next, identify all the blocks inside the scopes.
788 for (const MachineBasicBlock *MBB : EHScopeBlocks)
789 collectEHScopeMembers(EHScopeMembership, MBB->getNumber(), MBB);
790 // SEH CatchPads aren't really scopes, handle them separately.
791 for (const MachineBasicBlock *MBB : SEHCatchPads)
792 collectEHScopeMembers(EHScopeMembership, EntryBBNumber, MBB);
793 // Finally, identify all the targets of a catchret.
794 for (std::pair<const MachineBasicBlock *, int> CatchRetPair :
795 CatchRetSuccessors)
796 collectEHScopeMembers(EHScopeMembership, CatchRetPair.second,
797 CatchRetPair.first);
798 return EHScopeMembership;
799}