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).getValueAsString() == "true");     \
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   // DLLImport explicitly marks the GV as external.
119   if (GV->hasDLLImportStorageClass())
120     return false;
121 
122   // On MinGW, variables that haven't been declared with DLLImport may still
123   // end up automatically imported by the linker. To make this feasible,
124   // don't assume the variables to be DSO local unless we actually know
125   // that for sure. This only has to be done for variables; for functions
126   // the linker can insert thunks for calling functions from another DLL.
127   if (TT.isWindowsGNUEnvironment() && TT.isOSBinFormatCOFF() &&
128       GV->isDeclarationForLinker() && isa<GlobalVariable>(GV))
129     return false;
130 
131   // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
132   // remain unresolved in the link, they can be resolved to zero, which is
133   // outside the current DSO.
134   if (TT.isOSBinFormatCOFF() && GV->hasExternalWeakLinkage())
135     return false;
136 
137   // Every other GV is local on COFF.
138   // Make an exception for windows OS in the triple: Some firmware builds use
139   // *-win32-macho triples. This (accidentally?) produced windows relocations
140   // without GOT tables in older clang versions; Keep this behaviour.
141   // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables
142   // either.
143   if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
144     return true;
145 
146   if (TT.isOSBinFormatMachO()) {
147     if (RM == Reloc::Static)
148       return true;
149     return GV->isStrongDefinitionForLinker();
150   }
151 
152   // Due to the AIX linkage model, any global with default visibility is
153   // considered non-local.
154   if (TT.isOSBinFormatXCOFF())
155     return false;
156 
157   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm());
158   assert(RM != Reloc::DynamicNoPIC);
159 
160   bool IsExecutable =
161       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
162   if (IsExecutable) {
163     // If the symbol is defined, it cannot be preempted.
164     if (!GV->isDeclarationForLinker())
165       return true;
166   } else if (TT.isOSBinFormatELF()) {
167     // If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
168     // alias, set the flag. We cannot set dso_local for other global values,
169     // because otherwise direct accesses to a probably interposable symbol (even
170     // if the codegen assumes not) will be rejected by the linker.
171     if (!GV->canBenefitFromLocalAlias())
172       return false;
173     return TT.isX86() && M.noSemanticInterposition();
174   }
175 
176   // ELF & wasm support preemption of other symbols.
177   return false;
178 }
179 
180 bool TargetMachine::useEmulatedTLS() const {
181   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
182   // was specified explicitly; otherwise uses target triple to decide default.
183   if (Options.ExplicitEmulatedTLS)
184     return Options.EmulatedTLS;
185   return getTargetTriple().hasDefaultEmulatedTLS();
186 }
187 
188 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
189   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
190   Reloc::Model RM = getRelocationModel();
191   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
192   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
193 
194   TLSModel::Model Model;
195   if (IsSharedLibrary) {
196     if (IsLocal)
197       Model = TLSModel::LocalDynamic;
198     else
199       Model = TLSModel::GeneralDynamic;
200   } else {
201     if (IsLocal)
202       Model = TLSModel::LocalExec;
203     else
204       Model = TLSModel::InitialExec;
205   }
206 
207   // If the user specified a more specific model, use that.
208   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
209   if (SelectedModel > Model)
210     return SelectedModel;
211 
212   return Model;
213 }
214 
215 /// Returns the optimization level: None, Less, Default, or Aggressive.
216 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
217 
218 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
219 
220 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
221   return TargetTransformInfo(F.getParent()->getDataLayout());
222 }
223 
224 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
225                                       const GlobalValue *GV, Mangler &Mang,
226                                       bool MayAlwaysUsePrivate) const {
227   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
228     // Simple case: If GV is not private, it is not important to find out if
229     // private labels are legal in this case or not.
230     Mang.getNameWithPrefix(Name, GV, false);
231     return;
232   }
233   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
234   TLOF->getNameWithPrefix(Name, GV, *this);
235 }
236 
237 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
238   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
239   // XCOFF symbols could have special naming convention.
240   if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
241     return TargetSymbol;
242 
243   SmallString<128> NameStr;
244   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
245   return TLOF->getContext().getOrCreateSymbol(NameStr);
246 }
247 
248 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
249   // Since Analysis can't depend on Target, use a std::function to invert the
250   // dependency.
251   return TargetIRAnalysis(
252       [this](const Function &F) { return this->getTargetTransformInfo(F); });
253 }
254