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 
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/DataLayout.h"
20 #include "llvm/IR/DerivedTypes.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/GlobalVariable.h"
23 #include "llvm/IR/Mangler.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCExpr.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/MC/MCSymbol.h"
32 using namespace llvm;
33 
34 //===----------------------------------------------------------------------===//
35 // Generic Code
36 //===----------------------------------------------------------------------===//
37 
38 /// Initialize - this method must be called before any actual lowering is
39 /// done. This specifies the current context for codegen, and gives the
40 /// lowering implementations a chance to set up their default sections.
42  const TargetMachine &TM) {
43  Ctx = &ctx;
44  // `Initialize` can be called more than once.
45  delete Mang;
46  Mang = new Mangler();
49 }
50 
52  delete Mang;
53 }
54 
55 static bool isNullOrUndef(const Constant *C) {
56  // Check that the constant isn't all zeros or undefs.
57  if (C->isNullValue() || isa<UndefValue>(C))
58  return true;
59  if (!isa<ConstantAggregate>(C))
60  return false;
61  for (auto Operand : C->operand_values()) {
62  if (!isNullOrUndef(cast<Constant>(Operand)))
63  return false;
64  }
65  return true;
66 }
67 
68 static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS) {
69  const Constant *C = GV->getInitializer();
70 
71  // Must have zero initializer.
72  if (!isNullOrUndef(C))
73  return false;
74 
75  // Leave constant zeros in readonly constant sections, so they can be shared.
76  if (GV->isConstant())
77  return false;
78 
79  // If the global has an explicit section specified, don't put it in BSS.
80  if (GV->hasSection())
81  return false;
82 
83  // If -nozero-initialized-in-bss is specified, don't ever use BSS.
84  if (NoZerosInBSS)
85  return false;
86 
87  // Otherwise, put it in BSS!
88  return true;
89 }
90 
91 /// IsNullTerminatedString - Return true if the specified constant (which is
92 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
93 /// nul value and contains no other nuls in it. Note that this is more general
94 /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
95 static bool IsNullTerminatedString(const Constant *C) {
96  // First check: is we have constant array terminated with zero
97  if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
98  unsigned NumElts = CDS->getNumElements();
99  assert(NumElts != 0 && "Can't have an empty CDS");
100 
101  if (CDS->getElementAsInteger(NumElts-1) != 0)
102  return false; // Not null terminated.
103 
104  // Verify that the null doesn't occur anywhere else in the string.
105  for (unsigned i = 0; i != NumElts-1; ++i)
106  if (CDS->getElementAsInteger(i) == 0)
107  return false;
108  return true;
109  }
110 
111  // Another possibility: [1 x i8] zeroinitializer
112  if (isa<ConstantAggregateZero>(C))
113  return cast<ArrayType>(C->getType())->getNumElements() == 1;
114 
115  return false;
116 }
117 
119  const GlobalValue *GV, StringRef Suffix, const TargetMachine &TM) const {
120  assert(!Suffix.empty());
121 
122  SmallString<60> NameStr;
123  NameStr += GV->getParent()->getDataLayout().getPrivateGlobalPrefix();
124  TM.getNameWithPrefix(NameStr, GV, *Mang);
125  NameStr.append(Suffix.begin(), Suffix.end());
126  return Ctx->getOrCreateSymbol(NameStr);
127 }
128 
130  const GlobalValue *GV, const TargetMachine &TM,
131  MachineModuleInfo *MMI) const {
132  return TM.getSymbol(GV);
133 }
134 
136  const DataLayout &,
137  const MCSymbol *Sym) const {
138 }
139 
140 
141 /// getKindForGlobal - This is a top-level target-independent classifier for
142 /// a global variable. Given an global variable and information from TM, it
143 /// classifies the global in a variety of ways that make various target
144 /// implementations simpler. The target implementation is free to ignore this
145 /// extra info of course.
147  const TargetMachine &TM){
149  "Can only be used for global definitions");
150 
151  Reloc::Model ReloModel = TM.getRelocationModel();
152 
153  // Early exit - functions should be always in text sections.
154  const auto *GVar = dyn_cast<GlobalVariable>(GO);
155  if (!GVar)
156  return SectionKind::getText();
157 
158  // Handle thread-local data first.
159  if (GVar->isThreadLocal()) {
160  if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
161  return SectionKind::getThreadBSS();
163  }
164 
165  // Variables with common linkage always get classified as common.
166  if (GVar->hasCommonLinkage())
167  return SectionKind::getCommon();
168 
169  // Variable can be easily put to BSS section.
170  if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
171  if (GVar->hasLocalLinkage())
172  return SectionKind::getBSSLocal();
173  else if (GVar->hasExternalLinkage())
174  return SectionKind::getBSSExtern();
175  return SectionKind::getBSS();
176  }
177 
178  const Constant *C = GVar->getInitializer();
179 
180  // If the global is marked constant, we can put it into a mergable section,
181  // a mergable string section, or general .data if it contains relocations.
182  if (GVar->isConstant()) {
183  // If the initializer for the global contains something that requires a
184  // relocation, then we may have to drop this into a writable data section
185  // even though it is marked const.
186  if (!C->needsRelocation()) {
187  // If the global is required to have a unique address, it can't be put
188  // into a mergable section: just drop it into the general read-only
189  // section instead.
190  if (!GVar->hasGlobalUnnamedAddr())
191  return SectionKind::getReadOnly();
192 
193  // If initializer is a null-terminated string, put it in a "cstring"
194  // section of the right width.
195  if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
196  if (IntegerType *ITy =
197  dyn_cast<IntegerType>(ATy->getElementType())) {
198  if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
199  ITy->getBitWidth() == 32) &&
201  if (ITy->getBitWidth() == 8)
203  if (ITy->getBitWidth() == 16)
205 
206  assert(ITy->getBitWidth() == 32 && "Unknown width");
208  }
209  }
210  }
211 
212  // Otherwise, just drop it into a mergable constant section. If we have
213  // a section for this size, use it, otherwise use the arbitrary sized
214  // mergable section.
215  switch (
216  GVar->getParent()->getDataLayout().getTypeAllocSize(C->getType())) {
217  case 4: return SectionKind::getMergeableConst4();
218  case 8: return SectionKind::getMergeableConst8();
219  case 16: return SectionKind::getMergeableConst16();
220  case 32: return SectionKind::getMergeableConst32();
221  default:
222  return SectionKind::getReadOnly();
223  }
224 
225  } else {
226  // In static, ROPI and RWPI relocation models, the linker will resolve
227  // all addresses, so the relocation entries will actually be constants by
228  // the time the app starts up. However, we can't put this into a
229  // mergable section, because the linker doesn't take relocations into
230  // consideration when it tries to merge entries in the section.
231  if (ReloModel == Reloc::Static || ReloModel == Reloc::ROPI ||
232  ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI)
233  return SectionKind::getReadOnly();
234 
235  // Otherwise, the dynamic linker needs to fix it up, put it in the
236  // writable data.rel section.
238  }
239  }
240 
241  // Okay, this isn't a constant.
242  return SectionKind::getData();
243 }
244 
245 /// This method computes the appropriate section to emit the specified global
246 /// variable or function definition. This should not be passed external (or
247 /// available externally) globals.
249  const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
250  // Select section name.
251  if (GO->hasSection())
252  return getExplicitSectionGlobal(GO, Kind, TM);
253 
254  if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
255  auto Attrs = GVar->getAttributes();
256  if ((Attrs.hasAttribute("bss-section") && Kind.isBSS()) ||
257  (Attrs.hasAttribute("data-section") && Kind.isData()) ||
258  (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly())) {
259  return getExplicitSectionGlobal(GO, Kind, TM);
260  }
261  }
262 
263  if (auto *F = dyn_cast<Function>(GO)) {
264  if (F->hasFnAttribute("implicit-section-name"))
265  return getExplicitSectionGlobal(GO, Kind, TM);
266  }
267 
268  // Use default section depending on the 'type' of global
269  return SelectSectionForGlobal(GO, Kind, TM);
270 }
271 
273  const Function &F, const TargetMachine &TM) const {
274  unsigned Align = 0;
276  SectionKind::getReadOnly(), /*C=*/nullptr,
277  Align);
278 }
279 
281  bool UsesLabelDifference, const Function &F) const {
282  // In PIC mode, we need to emit the jump table to the same section as the
283  // function body itself, otherwise the label differences won't make sense.
284  // FIXME: Need a better predicate for this: what about custom entries?
285  if (UsesLabelDifference)
286  return true;
287 
288  // We should also do if the section name is NULL or function is declared
289  // in discardable section
290  // FIXME: this isn't the right predicate, should be based on the MCSection
291  // for the function.
292  return F.isWeakForLinker();
293 }
294 
295 /// Given a mergable constant with the specified size and relocation
296 /// information, return a section that it should be placed in.
298  const DataLayout &DL, SectionKind Kind, const Constant *C,
299  unsigned &Align) const {
300  if (Kind.isReadOnly() && ReadOnlySection != nullptr)
301  return ReadOnlySection;
302 
303  return DataSection;
304 }
305 
306 /// getTTypeGlobalReference - Return an MCExpr to use for a
307 /// reference to the specified global variable from exception
308 /// handling information.
310  const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
311  MachineModuleInfo *MMI, MCStreamer &Streamer) const {
312  const MCSymbolRefExpr *Ref =
314 
315  return getTTypeReference(Ref, Encoding, Streamer);
316 }
317 
319 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
320  MCStreamer &Streamer) const {
321  switch (Encoding & 0x70) {
322  default:
323  report_fatal_error("We do not support this DWARF encoding yet!");
325  // Do nothing special
326  return Sym;
327  case dwarf::DW_EH_PE_pcrel: {
328  // Emit a label to the streamer for the current position. This gives us
329  // .-foo addressing.
330  MCSymbol *PCSym = getContext().createTempSymbol();
331  Streamer.EmitLabel(PCSym);
332  const MCExpr *PC = MCSymbolRefExpr::create(PCSym, getContext());
333  return MCBinaryExpr::createSub(Sym, PC, getContext());
334  }
335  }
336 }
337 
339  // FIXME: It's not clear what, if any, default this should have - perhaps a
340  // null return could mean 'no location' & we should just do that here.
341  return MCSymbolRefExpr::create(Sym, *Ctx);
342 }
343 
345  SmallVectorImpl<char> &OutName, const GlobalValue *GV,
346  const TargetMachine &TM) const {
347  Mang->getNameWithPrefix(OutName, GV, /*CannotUsePrivateLabel=*/false);
348 }
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:313
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:288
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:465
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
Represent a reference to a symbol from inside an expression.
Definition: MCExpr.h:165
void getNameWithPrefix(SmallVectorImpl< char > &Name, const GlobalValue *GV, Mangler &Mang, bool MayAlwaysUsePrivate=false) const
Context object for machine code objects.
Definition: MCContext.h:61
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:536
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:181
MCSymbol * createTempSymbol(bool CanBeUnnamed=true)
Create and return a new assembler temporary symbol with a unique but unspecified name.
Definition: MCContext.cpp:215
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
static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS)
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
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:121
bool isPositionIndependent() const
TargetOptions Options
Definition: TargetMachine.h:98
iterator_range< value_op_iterator > operand_values()
Definition: User.h:246
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:323
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
The access may reference the value stored in memory.
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:309
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:109
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.
This file describes how to lower LLVM code to machine code.
static SectionKind getText()
Definition: SectionKind.h:180