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/GlobalAlias.h"
17 #include "llvm/IR/GlobalValue.h"
18 #include "llvm/IR/GlobalVariable.h"
19 #include "llvm/IR/LegacyPassManager.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"
25 #include "llvm/MC/MCTargetOptions.h"
26 #include "llvm/MC/SectionKind.h"
27 #include "llvm/Target/TargetLoweringObjectFile.h"
28 using namespace llvm;
29 
30 //---------------------------------------------------------------------------
31 // TargetMachine Class
32 //
33 
34 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
35                              const Triple &TT, StringRef CPU, StringRef FS,
36                              const TargetOptions &Options)
37     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
38       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
39       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
40       O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
41 
42 TargetMachine::~TargetMachine() = default;
43 
44 bool TargetMachine::isPositionIndependent() const {
45   return getRelocationModel() == Reloc::PIC_;
46 }
47 
48 /// Reset the target options based on the function's attributes.
49 /// setFunctionAttributes should have made the raw attribute value consistent
50 /// with the command line flag if used.
51 //
52 // FIXME: This function needs to go away for a number of reasons:
53 // a) global state on the TargetMachine is terrible in general,
54 // b) these target options should be passed only on the function
55 //    and not on the TargetMachine (via TargetOptions) at all.
56 void TargetMachine::resetTargetOptions(const Function &F) const {
57 #define RESET_OPTION(X, Y)                                              \
58   do {                                                                  \
59     Options.X = F.getFnAttribute(Y).getValueAsBool();     \
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.
70 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
71 
72 /// Returns the code model. The choices are small, kernel, medium, large, and
73 /// target default.
74 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
75 
76 /// Get the IR-specified TLS model for Var.
77 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
78   switch (GV->getThreadLocalMode()) {
79   case GlobalVariable::NotThreadLocal:
80     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
81     break;
82   case GlobalVariable::GeneralDynamicTLSModel:
83     return TLSModel::GeneralDynamic;
84   case GlobalVariable::LocalDynamicTLSModel:
85     return TLSModel::LocalDynamic;
86   case GlobalVariable::InitialExecTLSModel:
87     return TLSModel::InitialExec;
88   case GlobalVariable::LocalExecTLSModel:
89     return TLSModel::LocalExec;
90   }
91   llvm_unreachable("invalid TLS model");
92 }
93 
94 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
95                                          const GlobalValue *GV) const {
96   const Triple &TT = getTargetTriple();
97   Reloc::Model RM = getRelocationModel();
98 
99   // According to the llvm language reference, we should be able to
100   // just return false in here if we have a GV, as we know it is
101   // dso_preemptable.  At this point in time, the various IR producers
102   // have not been transitioned to always produce a dso_local when it
103   // is possible to do so.
104   //
105   // As a result we still have some logic in here to improve the quality of the
106   // generated code.
107   if (!GV)
108     return false;
109 
110   // If the IR producer requested that this GV be treated as dso local, obey.
111   if (GV->isDSOLocal())
112     return true;
113 
114   if (TT.isOSBinFormatCOFF()) {
115     // DLLImport explicitly marks the GV as external.
116     if (GV->hasDLLImportStorageClass())
117       return false;
118 
119     // On MinGW, variables that haven't been declared with DLLImport may still
120     // end up automatically imported by the linker. To make this feasible,
121     // don't assume the variables to be DSO local unless we actually know
122     // that for sure. This only has to be done for variables; for functions
123     // the linker can insert thunks for calling functions from another DLL.
124     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
125         isa<GlobalVariable>(GV))
126       return false;
127 
128     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
129     // unresolved in the link, they can be resolved to zero, which is outside
130     // the current DSO.
131     if (GV->hasExternalWeakLinkage())
132       return false;
133 
134     // Every other GV is local on COFF.
135     return true;
136   }
137 
138   if (TT.isOSBinFormatGOFF())
139     return true;
140 
141   if (TT.isOSBinFormatMachO()) {
142     if (RM == Reloc::Static)
143       return true;
144     return GV->isStrongDefinitionForLinker();
145   }
146 
147   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
148          TT.isOSBinFormatXCOFF());
149   return false;
150 }
151 
152 bool TargetMachine::useEmulatedTLS() const {
153   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
154   // was specified explicitly; otherwise uses target triple to decide default.
155   if (Options.ExplicitEmulatedTLS)
156     return Options.EmulatedTLS;
157   return getTargetTriple().hasDefaultEmulatedTLS();
158 }
159 
160 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
161   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
162   Reloc::Model RM = getRelocationModel();
163   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
164   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
165 
166   TLSModel::Model Model;
167   if (IsSharedLibrary) {
168     if (IsLocal)
169       Model = TLSModel::LocalDynamic;
170     else
171       Model = TLSModel::GeneralDynamic;
172   } else {
173     if (IsLocal)
174       Model = TLSModel::LocalExec;
175     else
176       Model = TLSModel::InitialExec;
177   }
178 
179   // If the user specified a more specific model, use that.
180   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
181   if (SelectedModel > Model)
182     return SelectedModel;
183 
184   return Model;
185 }
186 
187 /// Returns the optimization level: None, Less, Default, or Aggressive.
188 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
189 
190 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
191 
192 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
193   return TargetTransformInfo(F.getParent()->getDataLayout());
194 }
195 
196 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
197                                       const GlobalValue *GV, Mangler &Mang,
198                                       bool MayAlwaysUsePrivate) const {
199   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
200     // Simple case: If GV is not private, it is not important to find out if
201     // private labels are legal in this case or not.
202     Mang.getNameWithPrefix(Name, GV, false);
203     return;
204   }
205   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
206   TLOF->getNameWithPrefix(Name, GV, *this);
207 }
208 
209 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
210   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
211   // XCOFF symbols could have special naming convention.
212   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
213     return TargetSymbol;
214 
215   SmallString<128> NameStr;
216   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
217   return TLOF->getContext().getOrCreateSymbol(NameStr);
218 }
219 
220 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
221   // Since Analysis can't depend on Target, use a std::function to invert the
222   // dependency.
223   return TargetIRAnalysis(
224       [this](const Function &F) { return this->getTargetTransformInfo(F); });
225 }
226 
227 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
228   if (Version == "none")
229     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
230   std::pair<int, int> Ret;
231   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
232     Version.consumeInteger(10, Ret.second);
233   return Ret;
234 }
235