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/GlobalValue.h"
17 #include "llvm/IR/GlobalVariable.h"
18 #include "llvm/IR/Mangler.h"
19 #include "llvm/MC/MCAsmInfo.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCInstrInfo.h"
22 #include "llvm/MC/MCRegisterInfo.h"
23 #include "llvm/MC/MCSubtargetInfo.h"
24 #include "llvm/Support/CodeGen.h"
25 #include "llvm/Target/TargetLoweringObjectFile.h"
26 using namespace llvm;
27 
28 //---------------------------------------------------------------------------
29 // TargetMachine Class
30 //
31 
32 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
33                              const Triple &TT, StringRef CPU, StringRef FS,
34                              const TargetOptions &Options)
35     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
36       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
37       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
38       O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
39 
40 TargetMachine::~TargetMachine() = default;
41 
42 bool TargetMachine::isLargeData() const {
43   if (getTargetTriple().getArch() != Triple::x86_64)
44     return false;
45   // Large data under the large code model still needs to be thought about, so
46   // restrict this to medium.
47   if (getCodeModel() != CodeModel::Medium)
48     return false;
49   return true;
50 }
51 
52 bool TargetMachine::isPositionIndependent() const {
53   return getRelocationModel() == Reloc::PIC_;
54 }
55 
56 /// Reset the target options based on the function's attributes.
57 /// setFunctionAttributes should have made the raw attribute value consistent
58 /// with the command line flag if used.
59 //
60 // FIXME: This function needs to go away for a number of reasons:
61 // a) global state on the TargetMachine is terrible in general,
62 // b) these target options should be passed only on the function
63 //    and not on the TargetMachine (via TargetOptions) at all.
64 void TargetMachine::resetTargetOptions(const Function &F) const {
65 #define RESET_OPTION(X, Y)                                              \
66   do {                                                                  \
67     Options.X = F.getFnAttribute(Y).getValueAsBool();     \
68   } while (0)
69 
70   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
71   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
72   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
73   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
74   RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
75 }
76 
77 /// Returns the code generation relocation model. The choices are static, PIC,
78 /// and dynamic-no-pic.
79 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
80 
81 /// Get the IR-specified TLS model for Var.
82 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
83   switch (GV->getThreadLocalMode()) {
84   case GlobalVariable::NotThreadLocal:
85     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
86     break;
87   case GlobalVariable::GeneralDynamicTLSModel:
88     return TLSModel::GeneralDynamic;
89   case GlobalVariable::LocalDynamicTLSModel:
90     return TLSModel::LocalDynamic;
91   case GlobalVariable::InitialExecTLSModel:
92     return TLSModel::InitialExec;
93   case GlobalVariable::LocalExecTLSModel:
94     return TLSModel::LocalExec;
95   }
96   llvm_unreachable("invalid TLS model");
97 }
98 
99 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
100                                          const GlobalValue *GV) const {
101   const Triple &TT = getTargetTriple();
102   Reloc::Model RM = getRelocationModel();
103 
104   // According to the llvm language reference, we should be able to
105   // just return false in here if we have a GV, as we know it is
106   // dso_preemptable.  At this point in time, the various IR producers
107   // have not been transitioned to always produce a dso_local when it
108   // is possible to do so.
109   //
110   // As a result we still have some logic in here to improve the quality of the
111   // generated code.
112   if (!GV)
113     return false;
114 
115   // If the IR producer requested that this GV be treated as dso local, obey.
116   if (GV->isDSOLocal())
117     return true;
118 
119   if (TT.isOSBinFormatCOFF()) {
120     // DLLImport explicitly marks the GV as external.
121     if (GV->hasDLLImportStorageClass())
122       return false;
123 
124     // On MinGW, variables that haven't been declared with DLLImport may still
125     // end up automatically imported by the linker. To make this feasible,
126     // don't assume the variables to be DSO local unless we actually know
127     // that for sure. This only has to be done for variables; for functions
128     // the linker can insert thunks for calling functions from another DLL.
129     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
130         isa<GlobalVariable>(GV))
131       return false;
132 
133     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
134     // unresolved in the link, they can be resolved to zero, which is outside
135     // the current DSO.
136     if (GV->hasExternalWeakLinkage())
137       return false;
138 
139     // Every other GV is local on COFF.
140     return true;
141   }
142 
143   if (TT.isOSBinFormatGOFF())
144     return true;
145 
146   if (TT.isOSBinFormatMachO()) {
147     if (RM == Reloc::Static)
148       return true;
149     return GV->isStrongDefinitionForLinker();
150   }
151 
152   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
153          TT.isOSBinFormatXCOFF());
154   return false;
155 }
156 
157 bool TargetMachine::useEmulatedTLS() const { return Options.EmulatedTLS; }
158 
159 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
160   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
161   Reloc::Model RM = getRelocationModel();
162   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
163   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
164 
165   TLSModel::Model Model;
166   if (IsSharedLibrary) {
167     if (IsLocal)
168       Model = TLSModel::LocalDynamic;
169     else
170       Model = TLSModel::GeneralDynamic;
171   } else {
172     if (IsLocal)
173       Model = TLSModel::LocalExec;
174     else
175       Model = TLSModel::InitialExec;
176   }
177 
178   // If the user specified a more specific model, use that.
179   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
180   if (SelectedModel > Model)
181     return SelectedModel;
182 
183   return Model;
184 }
185 
186 /// Returns the optimization level: None, Less, Default, or Aggressive.
187 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
188 
189 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
190 
191 TargetTransformInfo
192 TargetMachine::getTargetTransformInfo(const Function &F) const {
193   return TargetTransformInfo(F.getParent()->getDataLayout());
194 }
195 
196 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
197                                       const GlobalValue *GV, Mangler &Mang,
198                                       bool MayAlwaysUsePrivate) const {
199   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
200     // Simple case: If GV is not private, it is not important to find out if
201     // private labels are legal in this case or not.
202     Mang.getNameWithPrefix(Name, GV, false);
203     return;
204   }
205   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
206   TLOF->getNameWithPrefix(Name, GV, *this);
207 }
208 
209 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
210   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
211   // XCOFF symbols could have special naming convention.
212   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
213     return TargetSymbol;
214 
215   SmallString<128> NameStr;
216   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
217   return TLOF->getContext().getOrCreateSymbol(NameStr);
218 }
219 
220 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
221   // Since Analysis can't depend on Target, use a std::function to invert the
222   // dependency.
223   return TargetIRAnalysis(
224       [this](const Function &F) { return this->getTargetTransformInfo(F); });
225 }
226 
227 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
228   if (Version == "none")
229     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
230   std::pair<int, int> Ret;
231   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
232     Version.consumeInteger(10, Ret.second);
233   return Ret;
234 }
235