LLVM  7.0.0svn
TargetLoweringObjectFile.cpp
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1 //===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements classes used to handle lowerings specific to common
11 // object file formats.
12 //
13 //===----------------------------------------------------------------------===//
14 
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/DerivedTypes.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/GlobalVariable.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCStreamer.h"
26 #include "llvm/MC/MCSymbol.h"
31 using namespace llvm;
32 
33 //===----------------------------------------------------------------------===//
34 // Generic Code
35 //===----------------------------------------------------------------------===//
36 
37 /// Initialize - this method must be called before any actual lowering is
38 /// done. This specifies the current context for codegen, and gives the
39 /// lowering implementations a chance to set up their default sections.
41  const TargetMachine &TM) {
42  Ctx = &ctx;
43  // `Initialize` can be called more than once.
44  delete Mang;
45  Mang = new Mangler();
48 }
49 
51  delete Mang;
52 }
53 
54 static bool isNullOrUndef(const Constant *C) {
55  // Check that the constant isn't all zeros or undefs.
56  if (C->isNullValue() || isa<UndefValue>(C))
57  return true;
58  if (!isa<ConstantAggregate>(C))
59  return false;
60  for (auto Operand : C->operand_values()) {
61  if (!isNullOrUndef(cast<Constant>(Operand)))
62  return false;
63  }
64  return true;
65 }
66 
67 static bool isSuitableForBSS(const GlobalVariable *GV) {
68  const Constant *C = GV->getInitializer();
69 
70  // Must have zero initializer.
71  if (!isNullOrUndef(C))
72  return false;
73 
74  // Leave constant zeros in readonly constant sections, so they can be shared.
75  if (GV->isConstant())
76  return false;
77 
78  // If the global has an explicit section specified, don't put it in BSS.
79  if (GV->hasSection())
80  return false;
81 
82  // Otherwise, put it in BSS!
83  return true;
84 }
85 
86 /// IsNullTerminatedString - Return true if the specified constant (which is
87 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
88 /// nul value and contains no other nuls in it. Note that this is more general
89 /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
90 static bool IsNullTerminatedString(const Constant *C) {
91  // First check: is we have constant array terminated with zero
92  if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
93  unsigned NumElts = CDS->getNumElements();
94  assert(NumElts != 0 && "Can't have an empty CDS");
95 
96  if (CDS->getElementAsInteger(NumElts-1) != 0)
97  return false; // Not null terminated.
98 
99  // Verify that the null doesn't occur anywhere else in the string.
100  for (unsigned i = 0; i != NumElts-1; ++i)
101  if (CDS->getElementAsInteger(i) == 0)
102  return false;
103  return true;
104  }
105 
106  // Another possibility: [1 x i8] zeroinitializer
107  if (isa<ConstantAggregateZero>(C))
108  return cast<ArrayType>(C->getType())->getNumElements() == 1;
109 
110  return false;
111 }
112 
114  const GlobalValue *GV, StringRef Suffix, const TargetMachine &TM) const {
115  assert(!Suffix.empty());
116 
117  SmallString<60> NameStr;
118  NameStr += GV->getParent()->getDataLayout().getPrivateGlobalPrefix();
119  TM.getNameWithPrefix(NameStr, GV, *Mang);
120  NameStr.append(Suffix.begin(), Suffix.end());
121  return Ctx->getOrCreateSymbol(NameStr);
122 }
123 
125  const GlobalValue *GV, const TargetMachine &TM,
126  MachineModuleInfo *MMI) const {
127  return TM.getSymbol(GV);
128 }
129 
131  const DataLayout &,
132  const MCSymbol *Sym) const {
133 }
134 
135 
136 /// getKindForGlobal - This is a top-level target-independent classifier for
137 /// a global object. Given a global variable and information from the TM, this
138 /// function classifies the global in a target independent manner. This function
139 /// may be overridden by the target implementation.
141  const TargetMachine &TM){
143  "Can only be used for global definitions");
144 
145  // Functions are classified as text sections.
146  if (isa<Function>(GO))
147  return SectionKind::getText();
148 
149  // Global variables require more detailed analysis.
150  const auto *GVar = cast<GlobalVariable>(GO);
151 
152  // Handle thread-local data first.
153  if (GVar->isThreadLocal()) {
154  if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS)
155  return SectionKind::getThreadBSS();
157  }
158 
159  // Variables with common linkage always get classified as common.
160  if (GVar->hasCommonLinkage())
161  return SectionKind::getCommon();
162 
163  // Most non-mergeable zero data can be put in the BSS section unless otherwise
164  // specified.
165  if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS) {
166  if (GVar->hasLocalLinkage())
167  return SectionKind::getBSSLocal();
168  else if (GVar->hasExternalLinkage())
169  return SectionKind::getBSSExtern();
170  return SectionKind::getBSS();
171  }
172 
173  // If the global is marked constant, we can put it into a mergable section,
174  // a mergable string section, or general .data if it contains relocations.
175  if (GVar->isConstant()) {
176  // If the initializer for the global contains something that requires a
177  // relocation, then we may have to drop this into a writable data section
178  // even though it is marked const.
179  const Constant *C = GVar->getInitializer();
180  if (!C->needsRelocation()) {
181  // If the global is required to have a unique address, it can't be put
182  // into a mergable section: just drop it into the general read-only
183  // section instead.
184  if (!GVar->hasGlobalUnnamedAddr())
185  return SectionKind::getReadOnly();
186 
187  // If initializer is a null-terminated string, put it in a "cstring"
188  // section of the right width.
189  if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
190  if (IntegerType *ITy =
191  dyn_cast<IntegerType>(ATy->getElementType())) {
192  if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
193  ITy->getBitWidth() == 32) &&
195  if (ITy->getBitWidth() == 8)
197  if (ITy->getBitWidth() == 16)
199 
200  assert(ITy->getBitWidth() == 32 && "Unknown width");
202  }
203  }
204  }
205 
206  // Otherwise, just drop it into a mergable constant section. If we have
207  // a section for this size, use it, otherwise use the arbitrary sized
208  // mergable section.
209  switch (
210  GVar->getParent()->getDataLayout().getTypeAllocSize(C->getType())) {
211  case 4: return SectionKind::getMergeableConst4();
212  case 8: return SectionKind::getMergeableConst8();
213  case 16: return SectionKind::getMergeableConst16();
214  case 32: return SectionKind::getMergeableConst32();
215  default:
216  return SectionKind::getReadOnly();
217  }
218 
219  } else {
220  // In static, ROPI and RWPI relocation models, the linker will resolve
221  // all addresses, so the relocation entries will actually be constants by
222  // the time the app starts up. However, we can't put this into a
223  // mergable section, because the linker doesn't take relocations into
224  // consideration when it tries to merge entries in the section.
225  Reloc::Model ReloModel = TM.getRelocationModel();
226  if (ReloModel == Reloc::Static || ReloModel == Reloc::ROPI ||
227  ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI)
228  return SectionKind::getReadOnly();
229 
230  // Otherwise, the dynamic linker needs to fix it up, put it in the
231  // writable data.rel section.
233  }
234  }
235 
236  // Okay, this isn't a constant.
237  return SectionKind::getData();
238 }
239 
240 /// This method computes the appropriate section to emit the specified global
241 /// variable or function definition. This should not be passed external (or
242 /// available externally) globals.
244  const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
245  // Select section name.
246  if (GO->hasSection())
247  return getExplicitSectionGlobal(GO, Kind, TM);
248 
249  if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
250  auto Attrs = GVar->getAttributes();
251  if ((Attrs.hasAttribute("bss-section") && Kind.isBSS()) ||
252  (Attrs.hasAttribute("data-section") && Kind.isData()) ||
253  (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly())) {
254  return getExplicitSectionGlobal(GO, Kind, TM);
255  }
256  }
257 
258  if (auto *F = dyn_cast<Function>(GO)) {
259  if (F->hasFnAttribute("implicit-section-name"))
260  return getExplicitSectionGlobal(GO, Kind, TM);
261  }
262 
263  // Use default section depending on the 'type' of global
264  return SelectSectionForGlobal(GO, Kind, TM);
265 }
266 
268  const Function &F, const TargetMachine &TM) const {
269  unsigned Align = 0;
271  SectionKind::getReadOnly(), /*C=*/nullptr,
272  Align);
273 }
274 
276  bool UsesLabelDifference, const Function &F) const {
277  // In PIC mode, we need to emit the jump table to the same section as the
278  // function body itself, otherwise the label differences won't make sense.
279  // FIXME: Need a better predicate for this: what about custom entries?
280  if (UsesLabelDifference)
281  return true;
282 
283  // We should also do if the section name is NULL or function is declared
284  // in discardable section
285  // FIXME: this isn't the right predicate, should be based on the MCSection
286  // for the function.
287  return F.isWeakForLinker();
288 }
289 
290 /// Given a mergable constant with the specified size and relocation
291 /// information, return a section that it should be placed in.
293  const DataLayout &DL, SectionKind Kind, const Constant *C,
294  unsigned &Align) const {
295  if (Kind.isReadOnly() && ReadOnlySection != nullptr)
296  return ReadOnlySection;
297 
298  return DataSection;
299 }
300 
301 /// getTTypeGlobalReference - Return an MCExpr to use for a
302 /// reference to the specified global variable from exception
303 /// handling information.
305  const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
306  MachineModuleInfo *MMI, MCStreamer &Streamer) const {
307  const MCSymbolRefExpr *Ref =
309 
310  return getTTypeReference(Ref, Encoding, Streamer);
311 }
312 
314 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
315  MCStreamer &Streamer) const {
316  switch (Encoding & 0x70) {
317  default:
318  report_fatal_error("We do not support this DWARF encoding yet!");
320  // Do nothing special
321  return Sym;
322  case dwarf::DW_EH_PE_pcrel: {
323  // Emit a label to the streamer for the current position. This gives us
324  // .-foo addressing.
325  MCSymbol *PCSym = getContext().createTempSymbol();
326  Streamer.EmitLabel(PCSym);
327  const MCExpr *PC = MCSymbolRefExpr::create(PCSym, getContext());
328  return MCBinaryExpr::createSub(Sym, PC, getContext());
329  }
330  }
331 }
332 
334  // FIXME: It's not clear what, if any, default this should have - perhaps a
335  // null return could mean 'no location' & we should just do that here.
336  return MCSymbolRefExpr::create(Sym, *Ctx);
337 }
338 
340  SmallVectorImpl<char> &OutName, const GlobalValue *GV,
341  const TargetMachine &TM) const {
342  Mang->getNameWithPrefix(OutName, GV, /*CannotUsePrivateLabel=*/false);
343 }
uint64_t CallInst * C
Instances of this class represent a uniqued identifier for a section in the current translation unit...
Definition: MCSection.h:39
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:111
constexpr char Align[]
Key for Kernel::Arg::Metadata::mAlign.
static SectionKind getData()
Definition: SectionKind.h:202
static bool isNullOrUndef(const Constant *C)
static const MCSymbolRefExpr * create(const MCSymbol *Symbol, MCContext &Ctx)
Definition: MCExpr.h:321
static SectionKind getMergeableConst32()
Definition: SectionKind.h:195
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:115
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
virtual void emitPersonalityValue(MCStreamer &Streamer, const DataLayout &TM, const MCSymbol *Sym) const
MCSection * SectionForGlobal(const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const
This method computes the appropriate section to emit the specified global variable or function defini...
StringRef getPrivateGlobalPrefix() const
Definition: DataLayout.h:294
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:42
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry...
Definition: Constants.cpp:478
bool hasAvailableExternallyLinkage() const
Definition: GlobalValue.h:422
static SectionKind getMergeableConst8()
Definition: SectionKind.h:193
static SectionKind getMergeableConst16()
Definition: SectionKind.h:194
static SectionKind getMergeable1ByteCString()
Definition: SectionKind.h:183
const MCExpr * getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding, MCStreamer &Streamer) const
static SectionKind getCommon()
Definition: SectionKind.h:201
F(f)
static SectionKind getMergeableConst4()
Definition: SectionKind.h:192
static SectionKind getBSS()
Definition: SectionKind.h:198
static SectionKind getMergeable4ByteCString()
Definition: SectionKind.h:189
const DataLayout & getDataLayout() const
Get the data layout for the module&#39;s target platform.
Definition: Module.cpp:361
virtual void Initialize(MCContext &ctx, const TargetMachine &TM)
This method must be called before any actual lowering is done.
bool isConstant() const
If the value is a global constant, its value is immutable throughout the runtime execution of the pro...
Base class for the full range of assembler expressions which are needed for parsing.
Definition: MCExpr.h:36
The access may reference the value stored in memory.
Represent a reference to a symbol from inside an expression.
Definition: MCExpr.h:166
void getNameWithPrefix(SmallVectorImpl< char > &Name, const GlobalValue *GV, Mangler &Mang, bool MayAlwaysUsePrivate=false) const
Context object for machine code objects.
Definition: MCContext.h:63
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:85
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
static const MCBinaryExpr * createSub(const MCExpr *LHS, const MCExpr *RHS, MCContext &Ctx)
Definition: MCExpr.h:544
ConstantDataSequential - A vector or array constant whose element type is a simple 1/2/4/8-byte integ...
Definition: Constants.h:570
Class to represent array types.
Definition: DerivedTypes.h:369
LLVM_NODISCARD LLVM_ATTRIBUTE_ALWAYS_INLINE bool empty() const
empty - Check if the string is empty.
Definition: StringRef.h:133
SmallString - A SmallString is just a SmallVector with methods and accessors that make it work better...
Definition: SmallString.h:26
Reloc::Model getRelocationModel() const
Returns the code generation relocation model.
static SectionKind getThreadData()
Definition: SectionKind.h:197
constexpr char Attrs[]
Key for Kernel::Metadata::mAttrs.
MCSection * DataSection
Section directive for standard data.
static bool isWeakForLinker(LinkageTypes Linkage)
Whether the definition of this global may be replaced at link time.
Definition: GlobalValue.h:369
static SectionKind getBSSLocal()
Definition: SectionKind.h:199
Streaming machine code generation interface.
Definition: MCStreamer.h:183
MCSymbol * createTempSymbol(bool CanBeUnnamed=true)
Create and return a new assembler temporary symbol with a unique but unspecified name.
Definition: MCContext.cpp:217
virtual bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference, const Function &F) const
This is an important base class in LLVM.
Definition: Constant.h:42
This file contains the declarations for the subclasses of Constant, which represent the different fla...
virtual MCSection * getSectionForConstant(const DataLayout &DL, SectionKind Kind, const Constant *C, unsigned &Align) const
Given a constant with the SectionKind, return a section that it should be placed in.
MCSymbol * getSymbol(const GlobalValue *GV) const
MCSymbol * getSymbolWithGlobalValueBase(const GlobalValue *GV, StringRef Suffix, const TargetMachine &TM) const
Return the MCSymbol for a private symbol with global value name as its base, with the specified suffi...
SectionKind - This is a simple POD value that classifies the properties of a section.
Definition: SectionKind.h:23
const Triple & getTargetTriple() const
virtual const MCExpr * getTTypeGlobalReference(const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM, MachineModuleInfo *MMI, MCStreamer &Streamer) const
Return an MCExpr to use for a reference to the specified global variable from exception handling info...
Class to represent integer types.
Definition: DerivedTypes.h:40
unsigned NoZerosInBSS
NoZerosInBSS - By default some codegens place zero-initialized data to .bss section.
bool isBSS() const
Definition: SectionKind.h:160
static SectionKind getThreadBSS()
Definition: SectionKind.h:196
bool hasSection() const
Check if this global has a custom object file section.
Definition: GlobalObject.h:82
static SectionKind getReadOnlyWithRel()
Definition: SectionKind.h:203
static bool isSuitableForBSS(const GlobalVariable *GV)
This file contains constants used for implementing Dwarf debug support.
CodeModel::Model getCodeModel() const
Returns the code model.
iterator begin() const
Definition: StringRef.h:106
static bool IsNullTerminatedString(const Constant *C)
IsNullTerminatedString - Return true if the specified constant (which is known to have a type that is...
bool isReadOnly() const
Definition: SectionKind.h:123
static SectionKind getMergeable2ByteCString()
Definition: SectionKind.h:186
void InitMCObjectFileInfo(const Triple &TT, bool PIC, MCContext &ctx, bool LargeCodeModel=false)
MCSymbol * getOrCreateSymbol(const Twine &Name)
Lookup the symbol inside with the specified Name.
Definition: MCContext.cpp:123
bool isPositionIndependent() const
TargetOptions Options
Definition: TargetMachine.h:98
iterator_range< value_op_iterator > operand_values()
Definition: User.h:262
static SectionKind getBSSExtern()
Definition: SectionKind.h:200
virtual void getNameWithPrefix(SmallVectorImpl< char > &OutName, const GlobalValue *GV, const TargetMachine &TM) const
virtual MCSection * getExplicitSectionGlobal(const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const =0
Targets should implement this method to assign a section to globals with an explicit section specfied...
bool isDeclaration() const
Return true if the primary definition of this global value is outside of the current translation unit...
Definition: Globals.cpp:201
const unsigned Kind
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:565
bool isData() const
Definition: SectionKind.h:166
virtual MCSection * SelectSectionForGlobal(const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const =0
virtual void EmitLabel(MCSymbol *Symbol, SMLoc Loc=SMLoc())
Emit a label for Symbol into the current section.
Definition: MCStreamer.cpp:322
Primary interface to the complete machine description for the target machine.
Definition: TargetMachine.h:59
void getNameWithPrefix(raw_ostream &OS, const GlobalValue *GV, bool CannotUsePrivateLabel) const
Print the appropriate prefix and the specified global variable&#39;s name.
Definition: Mangler.cpp:112
virtual MCSection * getSectionForJumpTable(const Function &F, const TargetMachine &TM) const
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
MCSection * ReadOnlySection
Section that is readonly and can contain arbitrary initialized data.
static SectionKind getKindForGlobal(const GlobalObject *GO, const TargetMachine &TM)
Classify the specified global variable into a set of target independent categories embodied in Sectio...
virtual MCSymbol * getCFIPersonalitySymbol(const GlobalValue *GV, const TargetMachine &TM, MachineModuleInfo *MMI) const
virtual const MCExpr * getDebugThreadLocalSymbol(const MCSymbol *Sym) const
Create a symbol reference to describe the given TLS variable when emitting the address in debug info...
iterator end() const
Definition: StringRef.h:108
static SectionKind getReadOnly()
Definition: SectionKind.h:182
This class contains meta information specific to a module.
static SectionKind getText()
Definition: SectionKind.h:180