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 
13 #include "llvm/Target/TargetMachine.h"
14 #include "llvm/Analysis/TargetTransformInfo.h"
15 #include "llvm/IR/Function.h"
16 #include "llvm/IR/GlobalValue.h"
17 #include "llvm/IR/GlobalVariable.h"
18 #include "llvm/IR/Mangler.h"
19 #include "llvm/MC/MCAsmInfo.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCInstrInfo.h"
22 #include "llvm/MC/MCRegisterInfo.h"
23 #include "llvm/MC/MCSubtargetInfo.h"
24 #include "llvm/Target/TargetLoweringObjectFile.h"
25 using namespace llvm;
26 
27 //---------------------------------------------------------------------------
28 // TargetMachine Class
29 //
30 
31 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
32                              const Triple &TT, StringRef CPU, StringRef FS,
33                              const TargetOptions &Options)
34     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
35       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
36       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
37       O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
38 
39 TargetMachine::~TargetMachine() = default;
40 
41 bool TargetMachine::isPositionIndependent() const {
42   return getRelocationModel() == Reloc::PIC_;
43 }
44 
45 /// Reset the target options based on the function's attributes.
46 /// setFunctionAttributes should have made the raw attribute value consistent
47 /// with the command line flag if used.
48 //
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.
53 void TargetMachine::resetTargetOptions(const Function &F) const {
54 #define RESET_OPTION(X, Y)                                              \
55   do {                                                                  \
56     Options.X = F.getFnAttribute(Y).getValueAsBool();     \
57   } while (0)
58 
59   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
60   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
61   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
62   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
63   RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
64 }
65 
66 /// Returns the code generation relocation model. The choices are static, PIC,
67 /// and dynamic-no-pic.
68 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
69 
70 /// Get the IR-specified TLS model for Var.
71 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
72   switch (GV->getThreadLocalMode()) {
73   case GlobalVariable::NotThreadLocal:
74     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
75     break;
76   case GlobalVariable::GeneralDynamicTLSModel:
77     return TLSModel::GeneralDynamic;
78   case GlobalVariable::LocalDynamicTLSModel:
79     return TLSModel::LocalDynamic;
80   case GlobalVariable::InitialExecTLSModel:
81     return TLSModel::InitialExec;
82   case GlobalVariable::LocalExecTLSModel:
83     return TLSModel::LocalExec;
84   }
85   llvm_unreachable("invalid TLS model");
86 }
87 
88 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
89                                          const GlobalValue *GV) const {
90   const Triple &TT = getTargetTriple();
91   Reloc::Model RM = getRelocationModel();
92 
93   // According to the llvm language reference, we should be able to
94   // just return false in here if we have a GV, as we know it is
95   // dso_preemptable.  At this point in time, the various IR producers
96   // have not been transitioned to always produce a dso_local when it
97   // is possible to do so.
98   //
99   // As a result we still have some logic in here to improve the quality of the
100   // generated code.
101   if (!GV)
102     return false;
103 
104   // If the IR producer requested that this GV be treated as dso local, obey.
105   if (GV->isDSOLocal())
106     return true;
107 
108   if (TT.isOSBinFormatCOFF()) {
109     // DLLImport explicitly marks the GV as external.
110     if (GV->hasDLLImportStorageClass())
111       return false;
112 
113     // On MinGW, variables that haven't been declared with DLLImport may still
114     // end up automatically imported by the linker. To make this feasible,
115     // don't assume the variables to be DSO local unless we actually know
116     // that for sure. This only has to be done for variables; for functions
117     // the linker can insert thunks for calling functions from another DLL.
118     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
119         isa<GlobalVariable>(GV))
120       return false;
121 
122     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
123     // unresolved in the link, they can be resolved to zero, which is outside
124     // the current DSO.
125     if (GV->hasExternalWeakLinkage())
126       return false;
127 
128     // Every other GV is local on COFF.
129     return true;
130   }
131 
132   if (TT.isOSBinFormatGOFF())
133     return true;
134 
135   if (TT.isOSBinFormatMachO()) {
136     if (RM == Reloc::Static)
137       return true;
138     return GV->isStrongDefinitionForLinker();
139   }
140 
141   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
142          TT.isOSBinFormatXCOFF());
143   return false;
144 }
145 
146 bool TargetMachine::useEmulatedTLS() const {
147   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
148   // was specified explicitly; otherwise uses target triple to decide default.
149   if (Options.ExplicitEmulatedTLS)
150     return Options.EmulatedTLS;
151   return getTargetTriple().hasDefaultEmulatedTLS();
152 }
153 
154 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
155   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
156   Reloc::Model RM = getRelocationModel();
157   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
158   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
159 
160   TLSModel::Model Model;
161   if (IsSharedLibrary) {
162     if (IsLocal)
163       Model = TLSModel::LocalDynamic;
164     else
165       Model = TLSModel::GeneralDynamic;
166   } else {
167     if (IsLocal)
168       Model = TLSModel::LocalExec;
169     else
170       Model = TLSModel::InitialExec;
171   }
172 
173   // If the user specified a more specific model, use that.
174   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
175   if (SelectedModel > Model)
176     return SelectedModel;
177 
178   return Model;
179 }
180 
181 /// Returns the optimization level: None, Less, Default, or Aggressive.
182 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
183 
184 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
185 
186 TargetTransformInfo
187 TargetMachine::getTargetTransformInfo(const Function &F) const {
188   return TargetTransformInfo(F.getParent()->getDataLayout());
189 }
190 
191 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
192                                       const GlobalValue *GV, Mangler &Mang,
193                                       bool MayAlwaysUsePrivate) const {
194   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
195     // Simple case: If GV is not private, it is not important to find out if
196     // private labels are legal in this case or not.
197     Mang.getNameWithPrefix(Name, GV, false);
198     return;
199   }
200   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
201   TLOF->getNameWithPrefix(Name, GV, *this);
202 }
203 
204 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
205   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
206   // XCOFF symbols could have special naming convention.
207   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
208     return TargetSymbol;
209 
210   SmallString<128> NameStr;
211   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
212   return TLOF->getContext().getOrCreateSymbol(NameStr);
213 }
214 
215 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
216   // Since Analysis can't depend on Target, use a std::function to invert the
217   // dependency.
218   return TargetIRAnalysis(
219       [this](const Function &F) { return this->getTargetTransformInfo(F); });
220 }
221 
222 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
223   if (Version == "none")
224     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
225   std::pair<int, int> Ret;
226   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
227     Version.consumeInteger(10, Ret.second);
228   return Ret;
229 }
230