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
TargetMachine(const Target & T,StringRef DataLayoutString,const Triple & TT,StringRef CPU,StringRef FS,const TargetOptions & Options)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
isPositionIndependent() const44 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.
resetTargetOptions(const Function & F) const56 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.
getRelocationModel() const70 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
71
72 /// Returns the code model. The choices are small, kernel, medium, large, and
73 /// target default.
getCodeModel() const74 CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
75
76 /// Get the IR-specified TLS model for Var.
getSelectedTLSModel(const GlobalValue * GV)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
shouldAssumeDSOLocal(const Module & M,const GlobalValue * GV) const94 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
useEmulatedTLS() const180 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
getTLSModel(const GlobalValue * GV) const188 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.
getOptLevel() const216 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
217
setOptLevel(CodeGenOpt::Level Level)218 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
219
getTargetTransformInfo(const Function & F)220 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
221 return TargetTransformInfo(F.getParent()->getDataLayout());
222 }
223
getNameWithPrefix(SmallVectorImpl<char> & Name,const GlobalValue * GV,Mangler & Mang,bool MayAlwaysUsePrivate) const224 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
getSymbol(const GlobalValue * GV) const237 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
getTargetIRAnalysis()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