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), DefaultOptions(Options), 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) these target options should be passed only on the function
67 //    and not on the TargetMachine (via TargetOptions) at all.
68 void TargetMachine::resetTargetOptions(const Function &F) const {
69 #define RESET_OPTION(X, Y)                                                     \
70   do {                                                                         \
71     if (F.hasFnAttribute(Y))                                                   \
72       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
73     else                                                                       \
74       Options.X = DefaultOptions.X;                                            \
75   } while (0)
76 
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(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
81   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
82 
83   StringRef Denormal =
84     F.getFnAttribute("denormal-fp-math").getValueAsString();
85   if (Denormal == "ieee")
86     Options.FPDenormalMode = FPDenormal::IEEE;
87   else if (Denormal == "preserve-sign")
88     Options.FPDenormalMode = FPDenormal::PreserveSign;
89   else if (Denormal == "positive-zero")
90     Options.FPDenormalMode = FPDenormal::PositiveZero;
91   else
92     Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
93 }
94 
95 /// Returns the code generation relocation model. The choices are static, PIC,
96 /// and dynamic-no-pic.
97 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
98 
99 /// Returns the code model. The choices are small, kernel, medium, large, and
100 /// target default.
101 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
102 
103 /// Get the IR-specified TLS model for Var.
104 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
105   switch (GV->getThreadLocalMode()) {
106   case GlobalVariable::NotThreadLocal:
107     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
108     break;
109   case GlobalVariable::GeneralDynamicTLSModel:
110     return TLSModel::GeneralDynamic;
111   case GlobalVariable::LocalDynamicTLSModel:
112     return TLSModel::LocalDynamic;
113   case GlobalVariable::InitialExecTLSModel:
114     return TLSModel::InitialExec;
115   case GlobalVariable::LocalExecTLSModel:
116     return TLSModel::LocalExec;
117   }
118   llvm_unreachable("invalid TLS model");
119 }
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     bool IsAccessViaCopyRelocs =
158         Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
159     Triple::ArchType Arch = TT.getArch();
160     bool IsPPC =
161         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
162     // Check if we can use copy relocations. PowerPC has no copy relocations.
163     if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
164       return true;
165   }
166 
167   // ELF supports preemption of other symbols.
168   return false;
169 }
170 
171 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
172   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
173   Reloc::Model RM = getRelocationModel();
174   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
175   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
176 
177   TLSModel::Model Model;
178   if (IsSharedLibrary) {
179     if (IsLocal)
180       Model = TLSModel::LocalDynamic;
181     else
182       Model = TLSModel::GeneralDynamic;
183   } else {
184     if (IsLocal)
185       Model = TLSModel::LocalExec;
186     else
187       Model = TLSModel::InitialExec;
188   }
189 
190   // If the user specified a more specific model, use that.
191   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
192   if (SelectedModel > Model)
193     return SelectedModel;
194 
195   return Model;
196 }
197 
198 /// Returns the optimization level: None, Less, Default, or Aggressive.
199 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
200 
201 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
202 
203 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
204   return TargetIRAnalysis([](const Function &F) {
205     return TargetTransformInfo(F.getParent()->getDataLayout());
206   });
207 }
208 
209 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
210                                       const GlobalValue *GV, Mangler &Mang,
211                                       bool MayAlwaysUsePrivate) const {
212   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
213     // Simple case: If GV is not private, it is not important to find out if
214     // private labels are legal in this case or not.
215     Mang.getNameWithPrefix(Name, GV, false);
216     return;
217   }
218   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
219   TLOF->getNameWithPrefix(Name, GV, *this);
220 }
221 
222 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
223   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
224   SmallString<128> NameStr;
225   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
226   return TLOF->getContext().getOrCreateSymbol(NameStr);
227 }
228