LLVM  10.0.0svn
TargetMachine.cpp
Go to the documentation of this file.
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 }
67 
68 /// Returns the code generation relocation model. The choices are static, PIC,
69 /// and dynamic-no-pic.
71 
72 /// Returns the code model. The choices are small, kernel, medium, large, and
73 /// target default.
75 
76 /// Get the IR-specified TLS model for Var.
78  switch (GV->getThreadLocalMode()) {
80  llvm_unreachable("getSelectedTLSModel for non-TLS variable");
81  break;
87  return TLSModel::InitialExec;
89  return TLSModel::LocalExec;
90  }
91  llvm_unreachable("invalid TLS model");
92 }
93 
95  const GlobalValue *GV) const {
96  // If the IR producer requested that this GV be treated as dso local, obey.
97  if (GV && GV->isDSOLocal())
98  return true;
99 
100  // If we are not supossed to use a PLT, we cannot assume that intrinsics are
101  // local since the linker can convert some direct access to access via plt.
102  if (M.getRtLibUseGOT() && !GV)
103  return false;
104 
105  // According to the llvm language reference, we should be able to
106  // just return false in here if we have a GV, as we know it is
107  // dso_preemptable. At this point in time, the various IR producers
108  // have not been transitioned to always produce a dso_local when it
109  // is possible to do so.
110  // In the case of intrinsics, GV is null and there is nowhere to put
111  // dso_local. Returning false for those will produce worse code in some
112  // architectures. For example, on x86 the caller has to set ebx before calling
113  // a plt.
114  // As a result we still have some logic in here to improve the quality of the
115  // generated code.
116  // FIXME: Add a module level metadata for whether intrinsics should be assumed
117  // local.
118 
120  const Triple &TT = getTargetTriple();
121 
122  // DLLImport explicitly marks the GV as external.
123  if (GV && GV->hasDLLImportStorageClass())
124  return false;
125 
126  // On MinGW, variables that haven't been declared with DLLImport may still
127  // end up automatically imported by the linker. To make this feasible,
128  // don't assume the variables to be DSO local unless we actually know
129  // that for sure. This only has to be done for variables; for functions
130  // the linker can insert thunks for calling functions from another DLL.
131  if (TT.isWindowsGNUEnvironment() && TT.isOSBinFormatCOFF() && GV &&
132  GV->isDeclarationForLinker() && isa<GlobalVariable>(GV))
133  return false;
134 
135  // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
136  // remain unresolved in the link, they can be resolved to zero, which is
137  // outside the current DSO.
138  if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
139  return false;
140 
141  // Every other GV is local on COFF.
142  // Make an exception for windows OS in the triple: Some firmware builds use
143  // *-win32-macho triples. This (accidentally?) produced windows relocations
144  // without GOT tables in older clang versions; Keep this behaviour.
145  // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables
146  // either.
147  if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
148  return true;
149 
150  // Most PIC code sequences that assume that a symbol is local cannot
151  // produce a 0 if it turns out the symbol is undefined. While this
152  // is ABI and relocation depended, it seems worth it to handle it
153  // here.
154  if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
155  return false;
156 
157  if (GV && !GV->hasDefaultVisibility())
158  return true;
159 
160  if (TT.isOSBinFormatMachO()) {
161  if (RM == Reloc::Static)
162  return true;
163  return GV && GV->isStrongDefinitionForLinker();
164  }
165 
166  // Due to the AIX linkage model, any global with default visibility is
167  // considered non-local.
168  if (TT.isOSBinFormatXCOFF())
169  return false;
170 
173 
174  bool IsExecutable =
176  if (IsExecutable) {
177  // If the symbol is defined, it cannot be preempted.
178  if (GV && !GV->isDeclarationForLinker())
179  return true;
180 
181  // A symbol marked nonlazybind should not be accessed with a plt. If the
182  // symbol turns out to be external, the linker will convert a direct
183  // access to an access via the plt, so don't assume it is local.
184  const Function *F = dyn_cast_or_null<Function>(GV);
185  if (F && F->hasFnAttribute(Attribute::NonLazyBind))
186  return false;
187 
188  bool IsTLS = GV && GV->isThreadLocal();
189  bool IsAccessViaCopyRelocs =
190  GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
191  Triple::ArchType Arch = TT.getArch();
192  bool IsPPC =
193  Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
194  // Check if we can use copy relocations. PowerPC has no copy relocations.
195  if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
196  return true;
197  }
198 
199  // ELF & wasm support preemption of other symbols.
200  return false;
201 }
202 
204  // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
205  // was specified explicitly; otherwise uses target triple to decide default.
207  return Options.EmulatedTLS;
209 }
210 
212  bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
214  bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
215  bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
216 
218  if (IsSharedLibrary) {
219  if (IsLocal)
220  Model = TLSModel::LocalDynamic;
221  else
222  Model = TLSModel::GeneralDynamic;
223  } else {
224  if (IsLocal)
225  Model = TLSModel::LocalExec;
226  else
227  Model = TLSModel::InitialExec;
228  }
229 
230  // If the user specified a more specific model, use that.
231  TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
232  if (SelectedModel > Model)
233  return SelectedModel;
234 
235  return Model;
236 }
237 
238 /// Returns the optimization level: None, Less, Default, or Aggressive.
240 
242 
245 }
246 
248  const GlobalValue *GV, Mangler &Mang,
249  bool MayAlwaysUsePrivate) const {
250  if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
251  // Simple case: If GV is not private, it is not important to find out if
252  // private labels are legal in this case or not.
253  Mang.getNameWithPrefix(Name, GV, false);
254  return;
255  }
257  TLOF->getNameWithPrefix(Name, GV, *this);
258 }
259 
262  SmallString<128> NameStr;
263  getNameWithPrefix(NameStr, GV, TLOF->getMangler());
264  return TLOF->getContext().getOrCreateSymbol(NameStr);
265 }
266 
268  // Since Analysis can't depend on Target, use a std::function to invert the
269  // dependency.
270  return TargetIRAnalysis(
271  [this](const Function &F) { return this->getTargetTransformInfo(F); });
272 }
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:66
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
#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
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:129
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
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