1 //===-- TargetMachine.cpp - General Target Information ---------------------==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file describes the general parts of a Target machine.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Target/TargetMachine.h"
15 #include "llvm/Analysis/TargetTransformInfo.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/IR/Function.h"
18 #include "llvm/IR/GlobalAlias.h"
19 #include "llvm/IR/GlobalValue.h"
20 #include "llvm/IR/GlobalVariable.h"
21 #include "llvm/IR/LegacyPassManager.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/MC/MCAsmInfo.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCInstrInfo.h"
26 #include "llvm/MC/MCSectionMachO.h"
27 #include "llvm/MC/MCTargetOptions.h"
28 #include "llvm/MC/SectionKind.h"
29 #include "llvm/Target/TargetLowering.h"
30 #include "llvm/Target/TargetLoweringObjectFile.h"
31 #include "llvm/Target/TargetSubtargetInfo.h"
32 using namespace llvm;
33 
34 cl::opt<bool> EnableIPRA("enable-ipra", cl::init(false), cl::Hidden,
35                          cl::desc("Enable interprocedural register allocation "
36                                   "to reduce load/store at procedure calls."));
37 
38 //---------------------------------------------------------------------------
39 // TargetMachine Class
40 //
41 
42 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
43                              const Triple &TT, StringRef CPU, StringRef FS,
44                              const TargetOptions &Options)
45     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
46       TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
47       RequireStructuredCFG(false), Options(Options) {
48   if (EnableIPRA.getNumOccurrences())
49     this->Options.EnableIPRA = EnableIPRA;
50 }
51 
52 TargetMachine::~TargetMachine() {
53   delete AsmInfo;
54   delete MRI;
55   delete MII;
56   delete STI;
57 }
58 
59 bool TargetMachine::isPositionIndependent() const {
60   return getRelocationModel() == Reloc::PIC_;
61 }
62 
63 /// \brief Reset the target options based on the function's attributes.
64 // FIXME: This function needs to go away for a number of reasons:
65 // a) global state on the TargetMachine is terrible in general,
66 // b) there's no default state here to keep,
67 // c) these target options should be passed only on the function
68 //    and not on the TargetMachine (via TargetOptions) at all.
69 void TargetMachine::resetTargetOptions(const Function &F) const {
70 #define RESET_OPTION(X, Y)                                                     \
71   do {                                                                         \
72     if (F.hasFnAttribute(Y))                                                   \
73       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
74   } while (0)
75 
76   RESET_OPTION(LessPreciseFPMADOption, "less-precise-fpmad");
77   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
78   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
79   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
80   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
81 
82   StringRef Denormal =
83     F.getFnAttribute("denormal-fp-math").getValueAsString();
84   if (Denormal == "ieee")
85     Options.FPDenormalMode = FPDenormal::IEEE;
86   else if (Denormal == "preserve-sign")
87     Options.FPDenormalMode = FPDenormal::PreserveSign;
88   else if (Denormal == "positive-zero")
89     Options.FPDenormalMode = FPDenormal::PositiveZero;
90 }
91 
92 /// Returns the code generation relocation model. The choices are static, PIC,
93 /// and dynamic-no-pic.
94 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
95 
96 /// Returns the code model. The choices are small, kernel, medium, large, and
97 /// target default.
98 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
99 
100 /// Get the IR-specified TLS model for Var.
101 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
102   switch (GV->getThreadLocalMode()) {
103   case GlobalVariable::NotThreadLocal:
104     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
105     break;
106   case GlobalVariable::GeneralDynamicTLSModel:
107     return TLSModel::GeneralDynamic;
108   case GlobalVariable::LocalDynamicTLSModel:
109     return TLSModel::LocalDynamic;
110   case GlobalVariable::InitialExecTLSModel:
111     return TLSModel::InitialExec;
112   case GlobalVariable::LocalExecTLSModel:
113     return TLSModel::LocalExec;
114   }
115   llvm_unreachable("invalid TLS model");
116 }
117 
118 // FIXME: make this a proper option
119 static bool CanUseCopyRelocWithPIE = false;
120 
121 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
122                                          const GlobalValue *GV) const {
123   Reloc::Model RM = getRelocationModel();
124   const Triple &TT = getTargetTriple();
125 
126   // DLLImport explicitly marks the GV as external.
127   if (GV && GV->hasDLLImportStorageClass())
128     return false;
129 
130   // Every other GV is local on COFF.
131   // Make an exception for windows OS in the triple: Some firmwares builds use
132   // *-win32-macho triples. This (accidentally?) produced windows relocations
133   // without GOT tables in older clang versions; Keep this behaviour.
134   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
135     return true;
136 
137   if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility()))
138     return true;
139 
140   if (TT.isOSBinFormatMachO()) {
141     if (RM == Reloc::Static)
142       return true;
143     return GV && GV->isStrongDefinitionForLinker();
144   }
145 
146   assert(TT.isOSBinFormatELF());
147   assert(RM != Reloc::DynamicNoPIC);
148 
149   bool IsExecutable =
150       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
151   if (IsExecutable) {
152     // If the symbol is defined, it cannot be preempted.
153     if (GV && !GV->isDeclarationForLinker())
154       return true;
155 
156     bool IsTLS = GV && GV->isThreadLocal();
157     // Check if we can use copy relocations.
158     if (!IsTLS && (RM == Reloc::Static || CanUseCopyRelocWithPIE))
159       return true;
160   }
161 
162   // ELF supports preemption of other symbols.
163   return false;
164 }
165 
166 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
167   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
168   Reloc::Model RM = getRelocationModel();
169   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
170   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
171 
172   TLSModel::Model Model;
173   if (IsSharedLibrary) {
174     if (IsLocal)
175       Model = TLSModel::LocalDynamic;
176     else
177       Model = TLSModel::GeneralDynamic;
178   } else {
179     if (IsLocal)
180       Model = TLSModel::LocalExec;
181     else
182       Model = TLSModel::InitialExec;
183   }
184 
185   // If the user specified a more specific model, use that.
186   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
187   if (SelectedModel > Model)
188     return SelectedModel;
189 
190   return Model;
191 }
192 
193 /// Returns the optimization level: None, Less, Default, or Aggressive.
194 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
195 
196 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
197 
198 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
199   return TargetIRAnalysis([this](const Function &F) {
200     return TargetTransformInfo(F.getParent()->getDataLayout());
201   });
202 }
203 
204 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
205                                       const GlobalValue *GV, Mangler &Mang,
206                                       bool MayAlwaysUsePrivate) const {
207   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
208     // Simple case: If GV is not private, it is not important to find out if
209     // private labels are legal in this case or not.
210     Mang.getNameWithPrefix(Name, GV, false);
211     return;
212   }
213   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
214   TLOF->getNameWithPrefix(Name, GV, *this);
215 }
216 
217 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV, Mangler &Mang) const {
218   SmallString<128> NameStr;
219   getNameWithPrefix(NameStr, GV, Mang);
220   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
221   return TLOF->getContext().getOrCreateSymbol(NameStr);
222 }
223