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/MCRegisterInfo.h"
25 #include "llvm/MC/MCSectionMachO.h"
26 #include "llvm/MC/MCSubtargetInfo.h"
27 #include "llvm/MC/MCTargetOptions.h"
28 #include "llvm/MC/SectionKind.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 using namespace llvm;
31 
32 //---------------------------------------------------------------------------
33 // TargetMachine Class
34 //
35 
36 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
37                              const Triple &TT, StringRef CPU, StringRef FS,
38                              const TargetOptions &Options)
39     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
40       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
41       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
42       O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
43 
44 TargetMachine::~TargetMachine() = default;
45 
46 bool TargetMachine::isPositionIndependent() const {
47   return getRelocationModel() == Reloc::PIC_;
48 }
49 
50 /// Reset the target options based on the function's attributes.
51 /// setFunctionAttributes should have made the raw attribute value consistent
52 /// with the command line flag if used.
53 //
54 // FIXME: This function needs to go away for a number of reasons:
55 // a) global state on the TargetMachine is terrible in general,
56 // b) these target options should be passed only on the function
57 //    and not on the TargetMachine (via TargetOptions) at all.
58 void TargetMachine::resetTargetOptions(const Function &F) const {
59 #define RESET_OPTION(X, Y)                                              \
60   do {                                                                  \
61     Options.X = F.getFnAttribute(Y).getValueAsBool();     \
62   } while (0)
63 
64   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
65   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
66   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
67   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
68   RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
69 }
70 
71 /// Returns the code generation relocation model. The choices are static, PIC,
72 /// and dynamic-no-pic.
73 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
74 
75 /// Returns the code model. The choices are small, kernel, medium, large, and
76 /// target default.
77 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
78 
79 /// Get the IR-specified TLS model for Var.
80 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
81   switch (GV->getThreadLocalMode()) {
82   case GlobalVariable::NotThreadLocal:
83     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
84     break;
85   case GlobalVariable::GeneralDynamicTLSModel:
86     return TLSModel::GeneralDynamic;
87   case GlobalVariable::LocalDynamicTLSModel:
88     return TLSModel::LocalDynamic;
89   case GlobalVariable::InitialExecTLSModel:
90     return TLSModel::InitialExec;
91   case GlobalVariable::LocalExecTLSModel:
92     return TLSModel::LocalExec;
93   }
94   llvm_unreachable("invalid TLS model");
95 }
96 
97 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
98                                          const GlobalValue *GV) const {
99   const Triple &TT = getTargetTriple();
100   Reloc::Model RM = getRelocationModel();
101 
102   // According to the llvm language reference, we should be able to
103   // just return false in here if we have a GV, as we know it is
104   // dso_preemptable.  At this point in time, the various IR producers
105   // have not been transitioned to always produce a dso_local when it
106   // is possible to do so.
107   //
108   // As a result we still have some logic in here to improve the quality of the
109   // generated code.
110   if (!GV)
111     return false;
112 
113   // If the IR producer requested that this GV be treated as dso local, obey.
114   if (GV->isDSOLocal())
115     return true;
116 
117   if (TT.isOSBinFormatCOFF()) {
118     // DLLImport explicitly marks the GV as external.
119     if (GV->hasDLLImportStorageClass())
120       return false;
121 
122     // On MinGW, variables that haven't been declared with DLLImport may still
123     // end up automatically imported by the linker. To make this feasible,
124     // don't assume the variables to be DSO local unless we actually know
125     // that for sure. This only has to be done for variables; for functions
126     // the linker can insert thunks for calling functions from another DLL.
127     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
128         isa<GlobalVariable>(GV))
129       return false;
130 
131     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
132     // unresolved in the link, they can be resolved to zero, which is outside
133     // the current DSO.
134     if (GV->hasExternalWeakLinkage())
135       return false;
136 
137     // Every other GV is local on COFF.
138     return true;
139   }
140 
141   if (TT.isOSBinFormatGOFF())
142     return true;
143 
144   if (TT.isOSBinFormatMachO()) {
145     if (RM == Reloc::Static)
146       return true;
147     return GV->isStrongDefinitionForLinker();
148   }
149 
150   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
151          TT.isOSBinFormatXCOFF());
152   return false;
153 }
154 
155 bool TargetMachine::useEmulatedTLS() const {
156   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
157   // was specified explicitly; otherwise uses target triple to decide default.
158   if (Options.ExplicitEmulatedTLS)
159     return Options.EmulatedTLS;
160   return getTargetTriple().hasDefaultEmulatedTLS();
161 }
162 
163 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
164   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
165   Reloc::Model RM = getRelocationModel();
166   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
167   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
168 
169   TLSModel::Model Model;
170   if (IsSharedLibrary) {
171     if (IsLocal)
172       Model = TLSModel::LocalDynamic;
173     else
174       Model = TLSModel::GeneralDynamic;
175   } else {
176     if (IsLocal)
177       Model = TLSModel::LocalExec;
178     else
179       Model = TLSModel::InitialExec;
180   }
181 
182   // If the user specified a more specific model, use that.
183   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
184   if (SelectedModel > Model)
185     return SelectedModel;
186 
187   return Model;
188 }
189 
190 /// Returns the optimization level: None, Less, Default, or Aggressive.
191 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
192 
193 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
194 
195 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
196   return TargetTransformInfo(F.getParent()->getDataLayout());
197 }
198 
199 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
200                                       const GlobalValue *GV, Mangler &Mang,
201                                       bool MayAlwaysUsePrivate) const {
202   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
203     // Simple case: If GV is not private, it is not important to find out if
204     // private labels are legal in this case or not.
205     Mang.getNameWithPrefix(Name, GV, false);
206     return;
207   }
208   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
209   TLOF->getNameWithPrefix(Name, GV, *this);
210 }
211 
212 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
213   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
214   // XCOFF symbols could have special naming convention.
215   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
216     return TargetSymbol;
217 
218   SmallString<128> NameStr;
219   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
220   return TLOF->getContext().getOrCreateSymbol(NameStr);
221 }
222 
223 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
224   // Since Analysis can't depend on Target, use a std::function to invert the
225   // dependency.
226   return TargetIRAnalysis(
227       [this](const Function &F) { return this->getTargetTransformInfo(F); });
228 }
229 
230 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
231   if (Version == "none")
232     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
233   std::pair<int, int> Ret;
234   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
235     Version.consumeInteger(10, Ret.second);
236   return Ret;
237 }
238