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 //---------------------------------------------------------------------------
35 // TargetMachine Class
36 //
37 
38 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
39                              const Triple &TT, StringRef CPU, StringRef FS,
40                              const TargetOptions &Options)
41     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
42       TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
43       RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) {
44 }
45 
46 TargetMachine::~TargetMachine() {
47   delete AsmInfo;
48   delete MRI;
49   delete MII;
50   delete STI;
51 }
52 
53 bool TargetMachine::isPositionIndependent() const {
54   return getRelocationModel() == Reloc::PIC_;
55 }
56 
57 /// \brief Reset the target options based on the function's attributes.
58 // FIXME: This function needs to go away for a number of reasons:
59 // a) global state on the TargetMachine is terrible in general,
60 // b) these target options should be passed only on the function
61 //    and not on the TargetMachine (via TargetOptions) at all.
62 void TargetMachine::resetTargetOptions(const Function &F) const {
63 #define RESET_OPTION(X, Y)                                                     \
64   do {                                                                         \
65     if (F.hasFnAttribute(Y))                                                   \
66       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
67     else                                                                       \
68       Options.X = DefaultOptions.X;                                            \
69   } while (0)
70 
71   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
72   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
73   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
74   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
75   RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
76 
77   StringRef Denormal =
78     F.getFnAttribute("denormal-fp-math").getValueAsString();
79   if (Denormal == "ieee")
80     Options.FPDenormalMode = FPDenormal::IEEE;
81   else if (Denormal == "preserve-sign")
82     Options.FPDenormalMode = FPDenormal::PreserveSign;
83   else if (Denormal == "positive-zero")
84     Options.FPDenormalMode = FPDenormal::PositiveZero;
85   else
86     Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
87 }
88 
89 /// Returns the code generation relocation model. The choices are static, PIC,
90 /// and dynamic-no-pic.
91 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
92 
93 /// Returns the code model. The choices are small, kernel, medium, large, and
94 /// target default.
95 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
96 
97 /// Get the IR-specified TLS model for Var.
98 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
99   switch (GV->getThreadLocalMode()) {
100   case GlobalVariable::NotThreadLocal:
101     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
102     break;
103   case GlobalVariable::GeneralDynamicTLSModel:
104     return TLSModel::GeneralDynamic;
105   case GlobalVariable::LocalDynamicTLSModel:
106     return TLSModel::LocalDynamic;
107   case GlobalVariable::InitialExecTLSModel:
108     return TLSModel::InitialExec;
109   case GlobalVariable::LocalExecTLSModel:
110     return TLSModel::LocalExec;
111   }
112   llvm_unreachable("invalid TLS model");
113 }
114 
115 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
116                                          const GlobalValue *GV) const {
117   // If the IR producer requested that this GV be treated as dso local, obey.
118   if (GV && GV->isDSOLocal())
119     return true;
120 
121   // According to the llvm language reference, we should be able to just return
122   // false in here if we have a GV, as we know it is dso_preemptable.
123   // At this point in time, the various IR producers have not been transitioned
124   // to always produce a dso_local when it is possible to do so. As a result we
125   // still have some pre-dso_local logic in here to improve the quality of the
126   // generated code:
127 
128   Reloc::Model RM = getRelocationModel();
129   const Triple &TT = getTargetTriple();
130 
131   // DLLImport explicitly marks the GV as external.
132   if (GV && GV->hasDLLImportStorageClass())
133     return false;
134 
135   // Every other GV is local on COFF.
136   // Make an exception for windows OS in the triple: Some firmwares builds use
137   // *-win32-macho triples. This (accidentally?) produced windows relocations
138   // without GOT tables in older clang versions; Keep this behaviour.
139   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
140     return true;
141 
142   // Most PIC code sequences that assume that a symbol is local cannot
143   // produce a 0 if it turns out the symbol is undefined. While this
144   // is ABI and relocation depended, it seems worth it to handle it
145   // here.
146   // FIXME: this is probably not ELF specific.
147   if (GV && isPositionIndependent() && TT.isOSBinFormatELF() &&
148       GV->hasExternalWeakLinkage())
149     return false;
150 
151   if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility()))
152     return true;
153 
154   if (TT.isOSBinFormatMachO()) {
155     if (RM == Reloc::Static)
156       return true;
157     return GV && GV->isStrongDefinitionForLinker();
158   }
159 
160   assert(TT.isOSBinFormatELF());
161   assert(RM != Reloc::DynamicNoPIC);
162 
163   bool IsExecutable =
164       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
165   if (IsExecutable) {
166     // If the symbol is defined, it cannot be preempted.
167     if (GV && !GV->isDeclarationForLinker())
168       return true;
169 
170     // A symbol marked nonlazybind should not be accessed with a plt. If the
171     // symbol turns out to be external, the linker will convert a direct
172     // access to an access via the plt, so don't assume it is local.
173     const Function *F = dyn_cast_or_null<Function>(GV);
174     if (F && F->hasFnAttribute(Attribute::NonLazyBind))
175       return false;
176 
177     bool IsTLS = GV && GV->isThreadLocal();
178     bool IsAccessViaCopyRelocs =
179         Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
180     Triple::ArchType Arch = TT.getArch();
181     bool IsPPC =
182         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
183     // Check if we can use copy relocations. PowerPC has no copy relocations.
184     if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
185       return true;
186   }
187 
188   // ELF supports preemption of other symbols.
189   return false;
190 }
191 
192 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
193   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
194   Reloc::Model RM = getRelocationModel();
195   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
196   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
197 
198   TLSModel::Model Model;
199   if (IsSharedLibrary) {
200     if (IsLocal)
201       Model = TLSModel::LocalDynamic;
202     else
203       Model = TLSModel::GeneralDynamic;
204   } else {
205     if (IsLocal)
206       Model = TLSModel::LocalExec;
207     else
208       Model = TLSModel::InitialExec;
209   }
210 
211   // If the user specified a more specific model, use that.
212   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
213   if (SelectedModel > Model)
214     return SelectedModel;
215 
216   return Model;
217 }
218 
219 /// Returns the optimization level: None, Less, Default, or Aggressive.
220 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
221 
222 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
223 
224 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
225   return TargetIRAnalysis([](const Function &F) {
226     return TargetTransformInfo(F.getParent()->getDataLayout());
227   });
228 }
229 
230 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
231                                       const GlobalValue *GV, Mangler &Mang,
232                                       bool MayAlwaysUsePrivate) const {
233   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
234     // Simple case: If GV is not private, it is not important to find out if
235     // private labels are legal in this case or not.
236     Mang.getNameWithPrefix(Name, GV, false);
237     return;
238   }
239   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
240   TLOF->getNameWithPrefix(Name, GV, *this);
241 }
242 
243 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
244   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
245   SmallString<128> NameStr;
246   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
247   return TLOF->getContext().getOrCreateSymbol(NameStr);
248 }
249