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/CodeGen/MIRFormatter.h"
16 #include "llvm/IR/Function.h"
17 #include "llvm/IR/GlobalAlias.h"
18 #include "llvm/IR/GlobalValue.h"
19 #include "llvm/IR/GlobalVariable.h"
20 #include "llvm/IR/LegacyPassManager.h"
21 #include "llvm/IR/Mangler.h"
22 #include "llvm/MC/MCAsmInfo.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCSectionMachO.h"
26 #include "llvm/MC/MCTargetOptions.h"
27 #include "llvm/MC/SectionKind.h"
28 #include "llvm/Target/TargetLoweringObjectFile.h"
29 using namespace llvm;
30 
31 //---------------------------------------------------------------------------
32 // TargetMachine Class
33 //
34 
35 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
36                              const Triple &TT, StringRef CPU, StringRef FS,
37                              const TargetOptions &Options)
38     : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
39       TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
40       RequireStructuredCFG(false), O0WantsFastISel(false),
41       DefaultOptions(Options), Options(Options) {
42   MIRF = std::make_unique<MIRFormatter>();
43 }
44 
45 TargetMachine::~TargetMachine() = default;
46 
47 bool TargetMachine::isPositionIndependent() const {
48   return getRelocationModel() == Reloc::PIC_;
49 }
50 
51 /// Reset the target options based on the function's attributes.
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     if (F.hasFnAttribute(Y))                                                   \
60       Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
61     else                                                                       \
62       Options.X = DefaultOptions.X;                                            \
63   } while (0)
64 
65   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
66   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
67   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
68   RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
69 }
70 
71 /// Returns the code generation relocation model. The choices are static, PIC,
72 /// and dynamic-no-pic.
73 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
74 
75 /// Returns the code model. The choices are small, kernel, medium, large, and
76 /// target default.
77 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
78 
79 /// Get the IR-specified TLS model for Var.
80 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
81   switch (GV->getThreadLocalMode()) {
82   case GlobalVariable::NotThreadLocal:
83     llvm_unreachable("getSelectedTLSModel for non-TLS variable");
84     break;
85   case GlobalVariable::GeneralDynamicTLSModel:
86     return TLSModel::GeneralDynamic;
87   case GlobalVariable::LocalDynamicTLSModel:
88     return TLSModel::LocalDynamic;
89   case GlobalVariable::InitialExecTLSModel:
90     return TLSModel::InitialExec;
91   case GlobalVariable::LocalExecTLSModel:
92     return TLSModel::LocalExec;
93   }
94   llvm_unreachable("invalid TLS model");
95 }
96 
97 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
98                                          const GlobalValue *GV) const {
99   // If the IR producer requested that this GV be treated as dso local, obey.
100   if (GV && GV->isDSOLocal())
101     return true;
102 
103   // If we are not supossed to use a PLT, we cannot assume that intrinsics are
104   // local since the linker can convert some direct access to access via plt.
105   if (M.getRtLibUseGOT() && !GV)
106     return false;
107 
108   // According to the llvm language reference, we should be able to
109   // just return false in here if we have a GV, as we know it is
110   // dso_preemptable.  At this point in time, the various IR producers
111   // have not been transitioned to always produce a dso_local when it
112   // is possible to do so.
113   // In the case of intrinsics, GV is null and there is nowhere to put
114   // dso_local. Returning false for those will produce worse code in some
115   // architectures. For example, on x86 the caller has to set ebx before calling
116   // a plt.
117   // As a result we still have some logic in here to improve the quality of the
118   // generated code.
119   // FIXME: Add a module level metadata for whether intrinsics should be assumed
120   // local.
121 
122   Reloc::Model RM = getRelocationModel();
123   const Triple &TT = getTargetTriple();
124 
125   // DLLImport explicitly marks the GV as external.
126   if (GV && GV->hasDLLImportStorageClass())
127     return false;
128 
129   // On MinGW, variables that haven't been declared with DLLImport may still
130   // end up automatically imported by the linker. To make this feasible,
131   // don't assume the variables to be DSO local unless we actually know
132   // that for sure. This only has to be done for variables; for functions
133   // the linker can insert thunks for calling functions from another DLL.
134   if (TT.isWindowsGNUEnvironment() && TT.isOSBinFormatCOFF() && GV &&
135       GV->isDeclarationForLinker() && isa<GlobalVariable>(GV))
136     return false;
137 
138   // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
139   // remain unresolved in the link, they can be resolved to zero, which is
140   // outside the current DSO.
141   if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
142     return false;
143 
144   // Every other GV is local on COFF.
145   // Make an exception for windows OS in the triple: Some firmware builds use
146   // *-win32-macho triples. This (accidentally?) produced windows relocations
147   // without GOT tables in older clang versions; Keep this behaviour.
148   // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables
149   // either.
150   if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
151     return true;
152 
153   // Most PIC code sequences that assume that a symbol is local cannot
154   // produce a 0 if it turns out the symbol is undefined. While this
155   // is ABI and relocation depended, it seems worth it to handle it
156   // here.
157   if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
158     return false;
159 
160   if (GV && !GV->hasDefaultVisibility())
161     return true;
162 
163   if (TT.isOSBinFormatMachO()) {
164     if (RM == Reloc::Static)
165       return true;
166     return GV && GV->isStrongDefinitionForLinker();
167   }
168 
169   // Due to the AIX linkage model, any global with default visibility is
170   // considered non-local.
171   if (TT.isOSBinFormatXCOFF())
172     return false;
173 
174   assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm());
175   assert(RM != Reloc::DynamicNoPIC);
176 
177   bool IsExecutable =
178       RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
179   if (IsExecutable) {
180     // If the symbol is defined, it cannot be preempted.
181     if (GV && !GV->isDeclarationForLinker())
182       return true;
183 
184     // A symbol marked nonlazybind should not be accessed with a plt. If the
185     // symbol turns out to be external, the linker will convert a direct
186     // access to an access via the plt, so don't assume it is local.
187     const Function *F = dyn_cast_or_null<Function>(GV);
188     if (F && F->hasFnAttribute(Attribute::NonLazyBind))
189       return false;
190     Triple::ArchType Arch = TT.getArch();
191 
192     // PowerPC prefers avoiding copy relocations.
193     if (Arch == Triple::ppc || TT.isPPC64())
194       return false;
195 
196     // Check if we can use copy relocations.
197     if (!(GV && GV->isThreadLocal()) && RM == Reloc::Static)
198       return true;
199   }
200 
201   // ELF & wasm support preemption of other symbols.
202   return false;
203 }
204 
205 bool TargetMachine::useEmulatedTLS() const {
206   // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
207   // was specified explicitly; otherwise uses target triple to decide default.
208   if (Options.ExplicitEmulatedTLS)
209     return Options.EmulatedTLS;
210   return getTargetTriple().hasDefaultEmulatedTLS();
211 }
212 
213 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
214   bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
215   Reloc::Model RM = getRelocationModel();
216   bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
217   bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
218 
219   TLSModel::Model Model;
220   if (IsSharedLibrary) {
221     if (IsLocal)
222       Model = TLSModel::LocalDynamic;
223     else
224       Model = TLSModel::GeneralDynamic;
225   } else {
226     if (IsLocal)
227       Model = TLSModel::LocalExec;
228     else
229       Model = TLSModel::InitialExec;
230   }
231 
232   // If the user specified a more specific model, use that.
233   TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
234   if (SelectedModel > Model)
235     return SelectedModel;
236 
237   return Model;
238 }
239 
240 /// Returns the optimization level: None, Less, Default, or Aggressive.
241 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
242 
243 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
244 
245 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
246   return TargetTransformInfo(F.getParent()->getDataLayout());
247 }
248 
249 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
250                                       const GlobalValue *GV, Mangler &Mang,
251                                       bool MayAlwaysUsePrivate) const {
252   if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
253     // Simple case: If GV is not private, it is not important to find out if
254     // private labels are legal in this case or not.
255     Mang.getNameWithPrefix(Name, GV, false);
256     return;
257   }
258   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
259   TLOF->getNameWithPrefix(Name, GV, *this);
260 }
261 
262 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
263   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
264   SmallString<128> NameStr;
265   getNameWithPrefix(NameStr, GV, TLOF->getMangler());
266   return TLOF->getContext().getOrCreateSymbol(NameStr);
267 }
268 
269 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
270   // Since Analysis can't depend on Target, use a std::function to invert the
271   // dependency.
272   return TargetIRAnalysis(
273       [this](const Function &F) { return this->getTargetTransformInfo(F); });
274 }
275