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/GlobalAlias.h"
17 #include "llvm/IR/GlobalValue.h"
18 #include "llvm/IR/GlobalVariable.h"
19 #include "llvm/IR/LegacyPassManager.h"
20 #include "llvm/IR/Mangler.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCInstrInfo.h"
24 #include "llvm/MC/MCSectionMachO.h"
25 #include "llvm/MC/MCTargetOptions.h"
26 #include "llvm/MC/SectionKind.h"
27 #include "llvm/Target/TargetLoweringObjectFile.h"
28 using namespace llvm;
29 
30 //---------------------------------------------------------------------------
31 // TargetMachine Class
32 //
33 
34 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
35                              const Triple &TT, StringRef CPU, StringRef FS,
36                              const TargetOptions &Options)
37     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
38       TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
39       MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
40       O0WantsFastISel(false), DefaultOptions(Options), Options(Options) {}
41 
42 TargetMachine::~TargetMachine() = default;
43 
44 bool TargetMachine::isPositionIndependent() const {
45   return getRelocationModel() == Reloc::PIC_;
46 }
47 
48 /// Reset the target options based on the function's attributes.
49 /// setFunctionAttributes should have made the raw attribute value consistent
50 /// with the command line flag if used.
51 //
52 // FIXME: This function needs to go away for a number of reasons:
53 // a) global state on the TargetMachine is terrible in general,
54 // b) these target options should be passed only on the function
55 //    and not on the TargetMachine (via TargetOptions) at all.
56 void TargetMachine::resetTargetOptions(const Function &F) const {
57 #define RESET_OPTION(X, Y)                                              \
58   do {                                                                  \
59     Options.X = F.getFnAttribute(Y).getValueAsBool();     \
60   } while (0)
61 
62   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
63   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
64   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
65   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
66 }
67 
68 /// Returns the code generation relocation model. The choices are static, PIC,
69 /// and dynamic-no-pic.
70 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
71 
72 /// Returns the code model. The choices are small, kernel, medium, large, and
73 /// target default.
74 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
75 
76 /// Get the IR-specified TLS model for Var.
77 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
78   switch (GV->getThreadLocalMode()) {
79   case GlobalVariable::NotThreadLocal:
80     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
81     break;
82   case GlobalVariable::GeneralDynamicTLSModel:
83     return TLSModel::GeneralDynamic;
84   case GlobalVariable::LocalDynamicTLSModel:
85     return TLSModel::LocalDynamic;
86   case GlobalVariable::InitialExecTLSModel:
87     return TLSModel::InitialExec;
88   case GlobalVariable::LocalExecTLSModel:
89     return TLSModel::LocalExec;
90   }
91   llvm_unreachable("invalid TLS model");
92 }
93 
94 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
95                                          const GlobalValue *GV) const {
96   const Triple &TT = getTargetTriple();
97   Reloc::Model RM = getRelocationModel();
98 
99   // According to the llvm language reference, we should be able to
100   // just return false in here if we have a GV, as we know it is
101   // dso_preemptable.  At this point in time, the various IR producers
102   // have not been transitioned to always produce a dso_local when it
103   // is possible to do so.
104   // In the case of ExternalSymbolSDNode, GV is null and we should just return
105   // false. However, COFF currently relies on this to be true
106   //
107   // As a result we still have some logic in here to improve the quality of the
108   // generated code.
109   // FIXME: Add a module level metadata for whether intrinsics should be assumed
110   // local.
111   if (!GV)
112     return TT.isOSBinFormatCOFF();
113 
114   // If the IR producer requested that this GV be treated as dso local, obey.
115   if (GV->isDSOLocal())
116     return true;
117 
118   if (TT.isOSBinFormatCOFF()) {
119     // DLLImport explicitly marks the GV as external.
120     if (GV->hasDLLImportStorageClass())
121       return false;
122 
123     // On MinGW, variables that haven't been declared with DLLImport may still
124     // end up automatically imported by the linker. To make this feasible,
125     // don't assume the variables to be DSO local unless we actually know
126     // that for sure. This only has to be done for variables; for functions
127     // the linker can insert thunks for calling functions from another DLL.
128     if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
129         isa<GlobalVariable>(GV))
130       return false;
131 
132     // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
133     // unresolved in the link, they can be resolved to zero, which is outside
134     // the current DSO.
135     if (GV->hasExternalWeakLinkage())
136       return false;
137 
138     // Every other GV is local on COFF.
139     return true;
140   }
141 
142   if (TT.isOSBinFormatMachO()) {
143     // Make an exception for windows OS in the triple: Some firmware builds use
144     // *-win32-macho triples. This (accidentally?) produced windows relocations
145     // without GOT tables in older clang versions; Keep this behaviour.
146     if (TT.isOSWindows())
147       return true;
148 
149     if (RM == Reloc::Static)
150       return true;
151     return GV->isStrongDefinitionForLinker();
152   }
153 
154   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
155          TT.isOSBinFormatXCOFF());
156   return false;
157 }
158 
159 bool TargetMachine::useEmulatedTLS() const {
160   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
161   // was specified explicitly; otherwise uses target triple to decide default.
162   if (Options.ExplicitEmulatedTLS)
163     return Options.EmulatedTLS;
164   return getTargetTriple().hasDefaultEmulatedTLS();
165 }
166 
167 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
168   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
169   Reloc::Model RM = getRelocationModel();
170   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
171   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
172 
173   TLSModel::Model Model;
174   if (IsSharedLibrary) {
175     if (IsLocal)
176       Model = TLSModel::LocalDynamic;
177     else
178       Model = TLSModel::GeneralDynamic;
179   } else {
180     if (IsLocal)
181       Model = TLSModel::LocalExec;
182     else
183       Model = TLSModel::InitialExec;
184   }
185 
186   // If the user specified a more specific model, use that.
187   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
188   if (SelectedModel > Model)
189     return SelectedModel;
190 
191   return Model;
192 }
193 
194 /// Returns the optimization level: None, Less, Default, or Aggressive.
195 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
196 
197 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
198 
199 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
200   return TargetTransformInfo(F.getParent()->getDataLayout());
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   // XCOFF symbols could have special naming convention.
219   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
220     return TargetSymbol;
221 
222   SmallString<128> NameStr;
223   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
224   return TLOF->getContext().getOrCreateSymbol(NameStr);
225 }
226 
227 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
228   // Since Analysis can't depend on Target, use a std::function to invert the
229   // dependency.
230   return TargetIRAnalysis(
231       [this](const Function &F) { return this->getTargetTransformInfo(F); });
232 }
233 
234 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
235   if (Version == "none")
236     return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
237   std::pair<int, int> Ret;
238   if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
239     Version.consumeInteger(10, Ret.second);
240   return Ret;
241 }
242