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   RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
67 }
68 
69 /// Returns the code generation relocation model. The choices are static, PIC,
70 /// and dynamic-no-pic.
71 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
72 
73 /// Returns the code model. The choices are small, kernel, medium, large, and
74 /// target default.
75 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
76 
77 /// Get the IR-specified TLS model for Var.
78 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
79   switch (GV->getThreadLocalMode()) {
80   case GlobalVariable::NotThreadLocal:
81     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
82     break;
83   case GlobalVariable::GeneralDynamicTLSModel:
84     return TLSModel::GeneralDynamic;
85   case GlobalVariable::LocalDynamicTLSModel:
86     return TLSModel::LocalDynamic;
87   case GlobalVariable::InitialExecTLSModel:
88     return TLSModel::InitialExec;
89   case GlobalVariable::LocalExecTLSModel:
90     return TLSModel::LocalExec;
91   }
92   llvm_unreachable("invalid TLS model");
93 }
94 
95 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
96                                          const GlobalValue *GV) const {
97   const Triple &TT = getTargetTriple();
98   Reloc::Model RM = getRelocationModel();
99 
100   // According to the llvm language reference, we should be able to
101   // just return false in here if we have a GV, as we know it is
102   // dso_preemptable.  At this point in time, the various IR producers
103   // have not been transitioned to always produce a dso_local when it
104   // is possible to do so.
105   //
106   // As a result we still have some logic in here to improve the quality of the
107   // generated code.
108   if (!GV)
109     return false;
110 
111   // If the IR producer requested that this GV be treated as dso local, obey.
112   if (GV->isDSOLocal())
113     return true;
114 
115   if (TT.isOSBinFormatCOFF()) {
116     // DLLImport explicitly marks the GV as external.
117     if (GV->hasDLLImportStorageClass())
118       return false;
119 
120     // On MinGW, variables that haven't been declared with DLLImport may still
121     // end up automatically imported by the linker. To make this feasible,
122     // don't assume the variables to be DSO local unless we actually know
123     // that for sure. This only has to be done for variables; for functions
124     // the linker can insert thunks for calling functions from another DLL.
125     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
126         isa<GlobalVariable>(GV))
127       return false;
128 
129     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
130     // unresolved in the link, they can be resolved to zero, which is outside
131     // the current DSO.
132     if (GV->hasExternalWeakLinkage())
133       return false;
134 
135     // Every other GV is local on COFF.
136     return true;
137   }
138 
139   if (TT.isOSBinFormatGOFF())
140     return true;
141 
142   if (TT.isOSBinFormatMachO()) {
143     if (RM == Reloc::Static)
144       return true;
145     return GV->isStrongDefinitionForLinker();
146   }
147 
148   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
149          TT.isOSBinFormatXCOFF());
150   return false;
151 }
152 
153 bool TargetMachine::useEmulatedTLS() const {
154   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
155   // was specified explicitly; otherwise uses target triple to decide default.
156   if (Options.ExplicitEmulatedTLS)
157     return Options.EmulatedTLS;
158   return getTargetTriple().hasDefaultEmulatedTLS();
159 }
160 
161 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
162   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
163   Reloc::Model RM = getRelocationModel();
164   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
165   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
166 
167   TLSModel::Model Model;
168   if (IsSharedLibrary) {
169     if (IsLocal)
170       Model = TLSModel::LocalDynamic;
171     else
172       Model = TLSModel::GeneralDynamic;
173   } else {
174     if (IsLocal)
175       Model = TLSModel::LocalExec;
176     else
177       Model = TLSModel::InitialExec;
178   }
179 
180   // If the user specified a more specific model, use that.
181   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
182   if (SelectedModel > Model)
183     return SelectedModel;
184 
185   return Model;
186 }
187 
188 /// Returns the optimization level: None, Less, Default, or Aggressive.
189 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
190 
191 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
192 
193 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
194   return TargetTransformInfo(F.getParent()->getDataLayout());
195 }
196 
197 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
198                                       const GlobalValue *GV, Mangler &Mang,
199                                       bool MayAlwaysUsePrivate) const {
200   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
201     // Simple case: If GV is not private, it is not important to find out if
202     // private labels are legal in this case or not.
203     Mang.getNameWithPrefix(Name, GV, false);
204     return;
205   }
206   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
207   TLOF->getNameWithPrefix(Name, GV, *this);
208 }
209 
210 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
211   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
212   // XCOFF symbols could have special naming convention.
213   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
214     return TargetSymbol;
215 
216   SmallString<128> NameStr;
217   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
218   return TLOF->getContext().getOrCreateSymbol(NameStr);
219 }
220 
221 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
222   // Since Analysis can't depend on Target, use a std::function to invert the
223   // dependency.
224   return TargetIRAnalysis(
225       [this](const Function &F) { return this->getTargetTransformInfo(F); });
226 }
227 
228 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
229   if (Version == "none")
230     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
231   std::pair<int, int> Ret;
232   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
233     Version.consumeInteger(10, Ret.second);
234   return Ret;
235 }
236