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  // Every other GV is local on COFF.
148  // Make an exception for windows OS in the triple: Some firmware builds use
149  // *-win32-macho triples. This (accidentally?) produced windows relocations
150  // without GOT tables in older clang versions; Keep this behaviour.
151  if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
152  return true;
153 
154  // Most PIC code sequences that assume that a symbol is local cannot
155  // produce a 0 if it turns out the symbol is undefined. While this
156  // is ABI and relocation depended, it seems worth it to handle it
157  // here.
158  if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
159  return false;
160 
161  if (GV && !GV->hasDefaultVisibility())
162  return true;
163 
164  if (TT.isOSBinFormatMachO() || TT.isOSBinFormatWasm()) {
165  if (RM == Reloc::Static)
166  return true;
167  return GV && GV->isStrongDefinitionForLinker();
168  }
169 
170  assert(TT.isOSBinFormatELF());
172 
173  bool IsExecutable =
175  if (IsExecutable) {
176  // If the symbol is defined, it cannot be preempted.
177  if (GV && !GV->isDeclarationForLinker())
178  return true;
179 
180  // A symbol marked nonlazybind should not be accessed with a plt. If the
181  // symbol turns out to be external, the linker will convert a direct
182  // access to an access via the plt, so don't assume it is local.
183  const Function *F = dyn_cast_or_null<Function>(GV);
184  if (F && F->hasFnAttribute(Attribute::NonLazyBind))
185  return false;
186 
187  bool IsTLS = GV && GV->isThreadLocal();
188  bool IsAccessViaCopyRelocs =
189  GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
190  Triple::ArchType Arch = TT.getArch();
191  bool IsPPC =
192  Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
193  // Check if we can use copy relocations. PowerPC has no copy relocations.
194  if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
195  return true;
196  }
197 
198  // ELF supports preemption of other symbols.
199  return false;
200 }
201 
203  // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
204  // was specified explicitly; otherwise uses target triple to decide default.
206  return Options.EmulatedTLS;
208 }
209 
211  bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
213  bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
214  bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
215 
217  if (IsSharedLibrary) {
218  if (IsLocal)
219  Model = TLSModel::LocalDynamic;
220  else
221  Model = TLSModel::GeneralDynamic;
222  } else {
223  if (IsLocal)
224  Model = TLSModel::LocalExec;
225  else
226  Model = TLSModel::InitialExec;
227  }
228 
229  // If the user specified a more specific model, use that.
230  TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
231  if (SelectedModel > Model)
232  return SelectedModel;
233 
234  return Model;
235 }
236 
237 /// Returns the optimization level: None, Less, Default, or Aggressive.
239 
241 
244 }
245 
247  const GlobalValue *GV, Mangler &Mang,
248  bool MayAlwaysUsePrivate) const {
249  if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
250  // Simple case: If GV is not private, it is not important to find out if
251  // private labels are legal in this case or not.
252  Mang.getNameWithPrefix(Name, GV, false);
253  return;
254  }
256  TLOF->getNameWithPrefix(Name, GV, *this);
257 }
258 
261  SmallString<128> NameStr;
262  getNameWithPrefix(NameStr, GV, TLOF->getMangler());
263  return TLOF->getContext().getOrCreateSymbol(NameStr);
264 }
265 
267  // Since Analysis can't depend on Target, use a std::function to invert the
268  // dependency.
269  return TargetIRAnalysis(
270  [this](const Function &F) { return this->getTargetTransformInfo(F); });
271 }
bool isDeclarationForLinker() const
Definition: GlobalValue.h:523
TargetMachine(const Target &T, StringRef DataLayoutString, const Triple &TargetTriple, StringRef CPU, StringRef FS, const TargetOptions &Options)
ThreadLocalMode getThreadLocalMode() const
Definition: GlobalValue.h:254
MCTargetOptions MCOptions
Machine level options.
bool hasPrivateLinkage() const
Definition: GlobalValue.h:434
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:608
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:320
bool hasDLLImportStorageClass() const
Definition: GlobalValue.h:261
F(f)
bool hasExternalWeakLinkage() const
Definition: GlobalValue.h:436
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:279
bool hasDefaultEmulatedTLS() const
Tests whether the target uses emulated TLS as default.
Definition: Triple.h:709
#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:290
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:555
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:528
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:613
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:618
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.
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:536
MCSymbol * getOrCreateSymbol(const Twine &Name)
Lookup the symbol inside with the specified Name.
Definition: MCContext.cpp:123
StringRef getValueAsString() const
Return the attribute&#39;s value as a string.
Definition: Attributes.cpp:194
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:565
Attribute getFnAttribute(Attribute::AttrKind Kind) const
Return the attribute for the given attribute kind.
Definition: Function.h:330
bool hasDefaultVisibility() const
Definition: GlobalValue.h:233
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:246
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:623