LLVM  9.0.0svn
TargetMachine.cpp
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1 //===-- TargetMachine.cpp - General Target Information ---------------------==//
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 describes the general parts of a Target machine.
10 //
11 //===----------------------------------------------------------------------===//
12 
15 #include "llvm/IR/Function.h"
16 #include "llvm/IR/GlobalAlias.h"
17 #include "llvm/IR/GlobalValue.h"
18 #include "llvm/IR/GlobalVariable.h"
20 #include "llvm/IR/Mangler.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCInstrInfo.h"
24 #include "llvm/MC/MCSectionMachO.h"
26 #include "llvm/MC/SectionKind.h"
28 using namespace llvm;
29 
30 //---------------------------------------------------------------------------
31 // TargetMachine Class
32 //
33 
35  const Triple &TT, StringRef CPU, StringRef FS,
36  const TargetOptions &Options)
37  : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
38  TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
39  RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) {
40 }
41 
43 
45  return getRelocationModel() == Reloc::PIC_;
46 }
47 
48 /// Reset the target options based on the function's attributes.
49 // FIXME: This function needs to go away for a number of reasons:
50 // a) global state on the TargetMachine is terrible in general,
51 // b) these target options should be passed only on the function
52 // and not on the TargetMachine (via TargetOptions) at all.
54 #define RESET_OPTION(X, Y) \
55  do { \
56  if (F.hasFnAttribute(Y)) \
57  Options.X = (F.getFnAttribute(Y).getValueAsString() == "true"); \
58  else \
59  Options.X = DefaultOptions.X; \
60  } while (0)
61 
62  RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
63  RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
64  RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
65  RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
66  RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
67 
68  StringRef Denormal =
69  F.getFnAttribute("denormal-fp-math").getValueAsString();
70  if (Denormal == "ieee")
72  else if (Denormal == "preserve-sign")
74  else if (Denormal == "positive-zero")
76  else
78 }
79 
80 /// Returns the code generation relocation model. The choices are static, PIC,
81 /// and dynamic-no-pic.
83 
84 /// Returns the code model. The choices are small, kernel, medium, large, and
85 /// target default.
87 
88 /// Get the IR-specified TLS model for Var.
90  switch (GV->getThreadLocalMode()) {
92  llvm_unreachable("getSelectedTLSModel for non-TLS variable");
93  break;
99  return TLSModel::InitialExec;
101  return TLSModel::LocalExec;
102  }
103  llvm_unreachable("invalid TLS model");
104 }
105 
107  const GlobalValue *GV) const {
108  // If the IR producer requested that this GV be treated as dso local, obey.
109  if (GV && GV->isDSOLocal())
110  return true;
111 
112  // If we are not supossed to use a PLT, we cannot assume that intrinsics are
113  // local since the linker can convert some direct access to access via plt.
114  if (M.getRtLibUseGOT() && !GV)
115  return false;
116 
117  // According to the llvm language reference, we should be able to
118  // just return false in here if we have a GV, as we know it is
119  // dso_preemptable. At this point in time, the various IR producers
120  // have not been transitioned to always produce a dso_local when it
121  // is possible to do so.
122  // In the case of intrinsics, GV is null and there is nowhere to put
123  // dso_local. Returning false for those will produce worse code in some
124  // architectures. For example, on x86 the caller has to set ebx before calling
125  // a plt.
126  // As a result we still have some logic in here to improve the quality of the
127  // generated code.
128  // FIXME: Add a module level metadata for whether intrinsics should be assumed
129  // local.
130 
132  const Triple &TT = getTargetTriple();
133 
134  // DLLImport explicitly marks the GV as external.
135  if (GV && GV->hasDLLImportStorageClass())
136  return false;
137 
138  // On MinGW, variables that haven't been declared with DLLImport may still
139  // end up automatically imported by the linker. To make this feasible,
140  // don't assume the variables to be DSO local unless we actually know
141  // that for sure. This only has to be done for variables; for functions
142  // the linker can insert thunks for calling functions from another DLL.
143  if (TT.isWindowsGNUEnvironment() && GV && GV->isDeclarationForLinker() &&
144  isa<GlobalVariable>(GV))
145  return false;
146 
147  // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
148  // remain unresolved in the link, they can be resolved to zero, which is
149  // outside the current DSO.
150  if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
151  return false;
152 
153  // Every other GV is local on COFF.
154  // Make an exception for windows OS in the triple: Some firmware builds use
155  // *-win32-macho triples. This (accidentally?) produced windows relocations
156  // without GOT tables in older clang versions; Keep this behaviour.
157  if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
158  return true;
159 
160  // Most PIC code sequences that assume that a symbol is local cannot
161  // produce a 0 if it turns out the symbol is undefined. While this
162  // is ABI and relocation depended, it seems worth it to handle it
163  // here.
164  if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
165  return false;
166 
167  if (GV && !GV->hasDefaultVisibility())
168  return true;
169 
170  if (TT.isOSBinFormatMachO()) {
171  if (RM == Reloc::Static)
172  return true;
173  return GV && GV->isStrongDefinitionForLinker();
174  }
175 
176  // Due to the AIX linkage model, any global with default visibility is
177  // considered non-local.
178  if (TT.isOSBinFormatXCOFF())
179  return false;
180 
183 
184  bool IsExecutable =
186  if (IsExecutable) {
187  // If the symbol is defined, it cannot be preempted.
188  if (GV && !GV->isDeclarationForLinker())
189  return true;
190 
191  // A symbol marked nonlazybind should not be accessed with a plt. If the
192  // symbol turns out to be external, the linker will convert a direct
193  // access to an access via the plt, so don't assume it is local.
194  const Function *F = dyn_cast_or_null<Function>(GV);
195  if (F && F->hasFnAttribute(Attribute::NonLazyBind))
196  return false;
197 
198  bool IsTLS = GV && GV->isThreadLocal();
199  bool IsAccessViaCopyRelocs =
200  GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
201  Triple::ArchType Arch = TT.getArch();
202  bool IsPPC =
203  Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
204  // Check if we can use copy relocations. PowerPC has no copy relocations.
205  if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
206  return true;
207  }
208 
209  // ELF & wasm support preemption of other symbols.
210  return false;
211 }
212 
214  // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
215  // was specified explicitly; otherwise uses target triple to decide default.
217  return Options.EmulatedTLS;
219 }
220 
222  bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
224  bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
225  bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
226 
228  if (IsSharedLibrary) {
229  if (IsLocal)
230  Model = TLSModel::LocalDynamic;
231  else
232  Model = TLSModel::GeneralDynamic;
233  } else {
234  if (IsLocal)
235  Model = TLSModel::LocalExec;
236  else
237  Model = TLSModel::InitialExec;
238  }
239 
240  // If the user specified a more specific model, use that.
241  TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
242  if (SelectedModel > Model)
243  return SelectedModel;
244 
245  return Model;
246 }
247 
248 /// Returns the optimization level: None, Less, Default, or Aggressive.
250 
252 
255 }
256 
258  const GlobalValue *GV, Mangler &Mang,
259  bool MayAlwaysUsePrivate) const {
260  if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
261  // Simple case: If GV is not private, it is not important to find out if
262  // private labels are legal in this case or not.
263  Mang.getNameWithPrefix(Name, GV, false);
264  return;
265  }
267  TLOF->getNameWithPrefix(Name, GV, *this);
268 }
269 
272  SmallString<128> NameStr;
273  getNameWithPrefix(NameStr, GV, TLOF->getMangler());
274  return TLOF->getContext().getOrCreateSymbol(NameStr);
275 }
276 
278  // Since Analysis can't depend on Target, use a std::function to invert the
279  // dependency.
280  return TargetIRAnalysis(
281  [this](const Function &F) { return this->getTargetTransformInfo(F); });
282 }
bool isDeclarationForLinker() const
Definition: GlobalValue.h:533
TargetMachine(const Target &T, StringRef DataLayoutString, const Triple &TargetTriple, StringRef CPU, StringRef FS, const TargetOptions &Options)
ThreadLocalMode getThreadLocalMode() const
Definition: GlobalValue.h:258
MCTargetOptions MCOptions
Machine level options.
bool hasPrivateLinkage() const
Definition: GlobalValue.h:444
This class represents lattice values for constants.
Definition: AllocatorList.h:23
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:41
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:65
amdgpu Simplify well known AMD library false FunctionCallee Value const Twine & Name
bool isOSBinFormatELF() const
Tests whether the OS uses the ELF binary format.
Definition: Triple.h:623
static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV)
Get the IR-specified TLS model for Var.
Analysis pass providing the TargetTransformInfo.
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.h:323
bool hasDLLImportStorageClass() const
Definition: GlobalValue.h:265
F(f)
bool hasExternalWeakLinkage() const
Definition: GlobalValue.h:446
virtual ~TargetMachine()
CodeGenOpt::Level OptLevel
Definition: TargetMachine.h:90
void resetTargetOptions(const Function &F) const
Reset the target options based on the function&#39;s attributes.
const DataLayout & getDataLayout() const
Get the data layout for the module&#39;s target platform.
Definition: Module.cpp:369
bool isDSOLocal() const
Definition: GlobalValue.h:283
bool hasDefaultEmulatedTLS() const
Tests whether the target uses emulated TLS as default.
Definition: Triple.h:739
#define RESET_OPTION(X, Y)
void getNameWithPrefix(SmallVectorImpl< char > &Name, const GlobalValue *GV, Mangler &Mang, bool MayAlwaysUsePrivate=false) const
ArchType getArch() const
getArch - Get the parsed architecture type of this triple.
Definition: Triple.h:296
Reloc::Model getRelocationModel() const
Returns the code generation relocation model.
TLSModel::Model getTLSModel(const GlobalValue *GV) const
Returns the TLS model which should be used for the given global variable.
bool isWindowsGNUEnvironment() const
Definition: Triple.h:565
virtual TargetTransformInfo getTargetTransformInfo(const Function &F)
Return a TargetTransformInfo for a given function.
bool useEmulatedTLS() const
Returns true if this target uses emulated TLS.
bool isOSWindows() const
Tests whether the OS is Windows.
Definition: Triple.h:538
CodeGenOpt::Level getOptLevel() const
Returns the optimization level: None, Less, Default, or Aggressive.
unsigned const MachineRegisterInfo * MRI
bool shouldAssumeDSOLocal(const Module &M, const GlobalValue *GV) const
PIELevel::Level getPIELevel() const
Returns the PIE level (small or large model)
Definition: Module.cpp:502
unsigned ExplicitEmulatedTLS
Whether -emulated-tls or -no-emulated-tls is set.
bool isOSBinFormatCOFF() const
Tests whether the OS uses the COFF binary format.
Definition: Triple.h:628
CodeModel::Model CMModel
Definition: TargetMachine.h:89
TargetIRAnalysis getTargetIRAnalysis()
Get a TargetIRAnalysis appropriate for the target.
MCSymbol * getSymbol(const GlobalValue *GV) const
const Triple & getTargetTriple() const
bool isOSBinFormatMachO() const
Tests whether the environment is MachO.
Definition: Triple.h:633
FPDenormal::DenormalMode FPDenormalMode
FPDenormalMode - This flags specificies which denormal numbers the code is permitted to require...
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
Triple - Helper class for working with autoconf configuration names.
Definition: Triple.h:43
const TargetOptions DefaultOptions
virtual TargetLoweringObjectFile * getObjFileLowering() const
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
Target - Wrapper for Target specific information.
CodeModel::Model getCodeModel() const
Returns the code model.
bool isOSBinFormatXCOFF() const
Tests whether the OS uses the XCOFF binary format.
Definition: Triple.h:643
unsigned EmulatedTLS
EmulatedTLS - This flag enables emulated TLS model, using emutls function in the runtime library...
bool getRtLibUseGOT() const
Returns true if PLT should be avoided for RTLib calls.
Definition: Module.cpp:550
bool isStrongDefinitionForLinker() const
Returns true if this global&#39;s definition will be the one chosen by the linker.
Definition: GlobalValue.h:546
MCSymbol * getOrCreateSymbol(const Twine &Name)
Lookup the symbol inside with the specified Name.
Definition: MCContext.cpp:127
StringRef getValueAsString() const
Return the attribute&#39;s value as a string.
Definition: Attributes.cpp:223
bool isPositionIndependent() const
TargetOptions Options
void setOptLevel(CodeGenOpt::Level Level)
Overrides the optimization level.
virtual void getNameWithPrefix(SmallVectorImpl< char > &OutName, const GlobalValue *GV, const TargetMachine &TM) const
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:575
Attribute getFnAttribute(Attribute::AttrKind Kind) const
Return the attribute for the given attribute kind.
Definition: Function.h:333
bool hasDefaultVisibility() const
Definition: GlobalValue.h:237
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:111
bool isThreadLocal() const
If the value is "Thread Local", its value isn&#39;t shared by the threads.
Definition: GlobalValue.h:250
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
This pass exposes codegen information to IR-level passes.
bool isOSBinFormatWasm() const
Tests whether the OS uses the Wasm binary format.
Definition: Triple.h:638