1 //===-- TargetMachine.cpp - General Target Information ---------------------==//
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 describes the general parts of a Target machine.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Target/TargetMachine.h"
15 #include "llvm/Analysis/TargetTransformInfo.h"
16 #include "llvm/IR/Function.h"
17 #include "llvm/IR/GlobalAlias.h"
18 #include "llvm/IR/GlobalValue.h"
19 #include "llvm/IR/GlobalVariable.h"
20 #include "llvm/IR/LegacyPassManager.h"
21 #include "llvm/IR/Mangler.h"
22 #include "llvm/MC/MCAsmInfo.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCSectionMachO.h"
26 #include "llvm/MC/MCTargetOptions.h"
27 #include "llvm/MC/SectionKind.h"
28 #include "llvm/Target/TargetLoweringObjectFile.h"
29 using namespace llvm;
30 
31 //---------------------------------------------------------------------------
32 // TargetMachine Class
33 //
34 
35 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
36                              const Triple &TT, StringRef CPU, StringRef FS,
37                              const TargetOptions &Options)
38     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
39       TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
40       RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) {
41 }
42 
43 TargetMachine::~TargetMachine() = default;
44 
45 bool TargetMachine::isPositionIndependent() const {
46   return getRelocationModel() == Reloc::PIC_;
47 }
48 
49 /// Reset the target options based on the function's attributes.
50 // FIXME: This function needs to go away for a number of reasons:
51 // a) global state on the TargetMachine is terrible in general,
52 // b) these target options should be passed only on the function
53 //    and not on the TargetMachine (via TargetOptions) at all.
54 void TargetMachine::resetTargetOptions(const Function &F) const {
55 #define RESET_OPTION(X, Y)                                                     \
56   do {                                                                         \
57     if (F.hasFnAttribute(Y))                                                   \
58       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
59     else                                                                       \
60       Options.X = DefaultOptions.X;                                            \
61   } while (0)
62 
63   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
64   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
65   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
66   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
67   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
68 
69   StringRef Denormal =
70     F.getFnAttribute("denormal-fp-math").getValueAsString();
71   if (Denormal == "ieee")
72     Options.FPDenormalMode = FPDenormal::IEEE;
73   else if (Denormal == "preserve-sign")
74     Options.FPDenormalMode = FPDenormal::PreserveSign;
75   else if (Denormal == "positive-zero")
76     Options.FPDenormalMode = FPDenormal::PositiveZero;
77   else
78     Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
79 }
80 
81 /// Returns the code generation relocation model. The choices are static, PIC,
82 /// and dynamic-no-pic.
83 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
84 
85 /// Returns the code model. The choices are small, kernel, medium, large, and
86 /// target default.
87 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
88 
89 /// Get the IR-specified TLS model for Var.
90 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
91   switch (GV->getThreadLocalMode()) {
92   case GlobalVariable::NotThreadLocal:
93     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
94     break;
95   case GlobalVariable::GeneralDynamicTLSModel:
96     return TLSModel::GeneralDynamic;
97   case GlobalVariable::LocalDynamicTLSModel:
98     return TLSModel::LocalDynamic;
99   case GlobalVariable::InitialExecTLSModel:
100     return TLSModel::InitialExec;
101   case GlobalVariable::LocalExecTLSModel:
102     return TLSModel::LocalExec;
103   }
104   llvm_unreachable("invalid TLS model");
105 }
106 
107 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
108                                          const GlobalValue *GV) const {
109   // If the IR producer requested that this GV be treated as dso local, obey.
110   if (GV && GV->isDSOLocal())
111     return true;
112 
113   // If we are not supossed to use a PLT, we cannot assume that intrinsics are
114   // local since the linker can convert some direct access to access via plt.
115   if (M.getRtLibUseGOT() && !GV)
116     return false;
117 
118   // According to the llvm language reference, we should be able to
119   // just return false in here if we have a GV, as we know it is
120   // dso_preemptable.  At this point in time, the various IR producers
121   // have not been transitioned to always produce a dso_local when it
122   // is possible to do so.
123   // In the case of intrinsics, GV is null and there is nowhere to put
124   // dso_local. Returning false for those will produce worse code in some
125   // architectures. For example, on x86 the caller has to set ebx before calling
126   // a plt.
127   // As a result we still have some logic in here to improve the quality of the
128   // generated code.
129   // FIXME: Add a module level metadata for whether intrinsics should be assumed
130   // local.
131 
132   Reloc::Model RM = getRelocationModel();
133   const Triple &TT = getTargetTriple();
134 
135   // DLLImport explicitly marks the GV as external.
136   if (GV && GV->hasDLLImportStorageClass())
137     return false;
138 
139   // On MinGW, variables that haven't been declared with DLLImport may still
140   // end up automatically imported by the linker. To make this feasible,
141   // don't assume the variables to be DSO local unless we actually know
142   // that for sure. This only has to be done for variables; for functions
143   // the linker can insert thunks for calling functions from another DLL.
144   if (TT.isWindowsGNUEnvironment() && GV && GV->isDeclarationForLinker() &&
145       isa<GlobalVariable>(GV))
146     return false;
147 
148   // Every other GV is local on COFF.
149   // Make an exception for windows OS in the triple: Some firmware builds use
150   // *-win32-macho triples. This (accidentally?) produced windows relocations
151   // without GOT tables in older clang versions; Keep this behaviour.
152   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
153     return true;
154 
155   // Most PIC code sequences that assume that a symbol is local cannot
156   // produce a 0 if it turns out the symbol is undefined. While this
157   // is ABI and relocation depended, it seems worth it to handle it
158   // here.
159   if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
160     return false;
161 
162   if (GV && !GV->hasDefaultVisibility())
163     return true;
164 
165   if (TT.isOSBinFormatMachO()) {
166     if (RM == Reloc::Static)
167       return true;
168     return GV && GV->isStrongDefinitionForLinker();
169   }
170 
171   assert(TT.isOSBinFormatELF());
172   assert(RM != Reloc::DynamicNoPIC);
173 
174   bool IsExecutable =
175       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
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 supports preemption of other symbols.
200   return false;
201 }
202 
203 bool TargetMachine::useEmulatedTLS() const {
204   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
205   // was specified explicitly; otherwise uses target triple to decide default.
206   if (Options.ExplicitEmulatedTLS)
207     return Options.EmulatedTLS;
208   return getTargetTriple().hasDefaultEmulatedTLS();
209 }
210 
211 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
212   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
213   Reloc::Model RM = getRelocationModel();
214   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
215   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
216 
217   TLSModel::Model Model;
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.
239 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
240 
241 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
242 
243 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
244   return TargetTransformInfo(F.getParent()->getDataLayout());
245 }
246 
247 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
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   }
256   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
257   TLOF->getNameWithPrefix(Name, GV, *this);
258 }
259 
260 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
261   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
262   SmallString<128> NameStr;
263   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
264   return TLOF->getContext().getOrCreateSymbol(NameStr);
265 }
266 
267 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
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 }
273