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 /// Returns the code model. The choices are small, kernel, medium, large, and
71 /// target default.
72 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
73 
74 /// Get the IR-specified TLS model for Var.
75 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
76   switch (GV->getThreadLocalMode()) {
77   case GlobalVariable::NotThreadLocal:
78     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
79     break;
80   case GlobalVariable::GeneralDynamicTLSModel:
81     return TLSModel::GeneralDynamic;
82   case GlobalVariable::LocalDynamicTLSModel:
83     return TLSModel::LocalDynamic;
84   case GlobalVariable::InitialExecTLSModel:
85     return TLSModel::InitialExec;
86   case GlobalVariable::LocalExecTLSModel:
87     return TLSModel::LocalExec;
88   }
89   llvm_unreachable("invalid TLS model");
90 }
91 
92 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
93                                          const GlobalValue *GV) const {
94   const Triple &TT = getTargetTriple();
95   Reloc::Model RM = getRelocationModel();
96 
97   // According to the llvm language reference, we should be able to
98   // just return false in here if we have a GV, as we know it is
99   // dso_preemptable.  At this point in time, the various IR producers
100   // have not been transitioned to always produce a dso_local when it
101   // is possible to do so.
102   //
103   // As a result we still have some logic in here to improve the quality of the
104   // generated code.
105   if (!GV)
106     return false;
107 
108   // If the IR producer requested that this GV be treated as dso local, obey.
109   if (GV->isDSOLocal())
110     return true;
111 
112   if (TT.isOSBinFormatCOFF()) {
113     // DLLImport explicitly marks the GV as external.
114     if (GV->hasDLLImportStorageClass())
115       return false;
116 
117     // On MinGW, variables that haven't been declared with DLLImport may still
118     // end up automatically imported by the linker. To make this feasible,
119     // don't assume the variables to be DSO local unless we actually know
120     // that for sure. This only has to be done for variables; for functions
121     // the linker can insert thunks for calling functions from another DLL.
122     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
123         isa<GlobalVariable>(GV))
124       return false;
125 
126     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
127     // unresolved in the link, they can be resolved to zero, which is outside
128     // the current DSO.
129     if (GV->hasExternalWeakLinkage())
130       return false;
131 
132     // Every other GV is local on COFF.
133     return true;
134   }
135 
136   if (TT.isOSBinFormatGOFF())
137     return true;
138 
139   if (TT.isOSBinFormatMachO()) {
140     if (RM == Reloc::Static)
141       return true;
142     return GV->isStrongDefinitionForLinker();
143   }
144 
145   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
146          TT.isOSBinFormatXCOFF());
147   return false;
148 }
149 
150 bool TargetMachine::useEmulatedTLS() const {
151   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
152   // was specified explicitly; otherwise uses target triple to decide default.
153   if (Options.ExplicitEmulatedTLS)
154     return Options.EmulatedTLS;
155   return getTargetTriple().hasDefaultEmulatedTLS();
156 }
157 
158 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
159   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
160   Reloc::Model RM = getRelocationModel();
161   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
162   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
163 
164   TLSModel::Model Model;
165   if (IsSharedLibrary) {
166     if (IsLocal)
167       Model = TLSModel::LocalDynamic;
168     else
169       Model = TLSModel::GeneralDynamic;
170   } else {
171     if (IsLocal)
172       Model = TLSModel::LocalExec;
173     else
174       Model = TLSModel::InitialExec;
175   }
176 
177   // If the user specified a more specific model, use that.
178   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
179   if (SelectedModel > Model)
180     return SelectedModel;
181 
182   return Model;
183 }
184 
185 /// Returns the optimization level: None, Less, Default, or Aggressive.
186 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
187 
188 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
189 
190 TargetTransformInfo
191 TargetMachine::getTargetTransformInfo(const Function &F) const {
192   return TargetTransformInfo(F.getParent()->getDataLayout());
193 }
194 
195 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
196                                       const GlobalValue *GV, Mangler &Mang,
197                                       bool MayAlwaysUsePrivate) const {
198   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
199     // Simple case: If GV is not private, it is not important to find out if
200     // private labels are legal in this case or not.
201     Mang.getNameWithPrefix(Name, GV, false);
202     return;
203   }
204   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
205   TLOF->getNameWithPrefix(Name, GV, *this);
206 }
207 
208 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
209   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
210   // XCOFF symbols could have special naming convention.
211   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
212     return TargetSymbol;
213 
214   SmallString<128> NameStr;
215   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
216   return TLOF->getContext().getOrCreateSymbol(NameStr);
217 }
218 
219 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
220   // Since Analysis can't depend on Target, use a std::function to invert the
221   // dependency.
222   return TargetIRAnalysis(
223       [this](const Function &F) { return this->getTargetTransformInfo(F); });
224 }
225 
226 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
227   if (Version == "none")
228     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
229   std::pair<int, int> Ret;
230   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
231     Version.consumeInteger(10, Ret.second);
232   return Ret;
233 }
234