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 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
119                                          const GlobalValue *GV) const {
120   Reloc::Model RM = getRelocationModel();
121   const Triple &TT = getTargetTriple();
122 
123   // DLLImport explicitly marks the GV as external.
124   if (GV && GV->hasDLLImportStorageClass())
125     return false;
126 
127   // Every other GV is local on COFF.
128   // Make an exception for windows OS in the triple: Some firmwares builds use
129   // *-win32-macho triples. This (accidentally?) produced windows relocations
130   // without GOT tables in older clang versions; Keep this behaviour.
131   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
132     return true;
133 
134   if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility()))
135     return true;
136 
137   if (TT.isOSBinFormatMachO()) {
138     if (RM == Reloc::Static)
139       return true;
140     return GV && GV->isStrongDefinitionForLinker();
141   }
142 
143   assert(TT.isOSBinFormatELF());
144   assert(RM != Reloc::DynamicNoPIC);
145 
146   bool IsExecutable =
147       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
148   if (IsExecutable) {
149     // If the symbol is defined, it cannot be preempted.
150     if (GV && !GV->isDeclarationForLinker())
151       return true;
152 
153     bool IsTLS = GV && GV->isThreadLocal();
154     bool IsAccessViaCopyRelocs =
155         Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
156     // Check if we can use copy relocations.
157     if (!IsTLS && (RM == Reloc::Static || IsAccessViaCopyRelocs))
158       return true;
159   }
160 
161   // ELF supports preemption of other symbols.
162   return false;
163 }
164 
165 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
166   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
167   Reloc::Model RM = getRelocationModel();
168   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
169   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
170 
171   TLSModel::Model Model;
172   if (IsSharedLibrary) {
173     if (IsLocal)
174       Model = TLSModel::LocalDynamic;
175     else
176       Model = TLSModel::GeneralDynamic;
177   } else {
178     if (IsLocal)
179       Model = TLSModel::LocalExec;
180     else
181       Model = TLSModel::InitialExec;
182   }
183 
184   // If the user specified a more specific model, use that.
185   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
186   if (SelectedModel > Model)
187     return SelectedModel;
188 
189   return Model;
190 }
191 
192 /// Returns the optimization level: None, Less, Default, or Aggressive.
193 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
194 
195 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
196 
197 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
198   return TargetIRAnalysis([this](const Function &F) {
199     return TargetTransformInfo(F.getParent()->getDataLayout());
200   });
201 }
202 
203 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
204                                       const GlobalValue *GV, Mangler &Mang,
205                                       bool MayAlwaysUsePrivate) const {
206   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
207     // Simple case: If GV is not private, it is not important to find out if
208     // private labels are legal in this case or not.
209     Mang.getNameWithPrefix(Name, GV, false);
210     return;
211   }
212   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
213   TLOF->getNameWithPrefix(Name, GV, *this);
214 }
215 
216 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
217   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
218   SmallString<128> NameStr;
219   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
220   return TLOF->getContext().getOrCreateSymbol(NameStr);
221 }
222