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 // If the IR producer requested that this GV be treated as dso local, obey.
97 if (GV && GV->isDSOLocal())
98 return true;
99
100 // If we are not supossed to use a PLT, we cannot assume that intrinsics are
101 // local since the linker can convert some direct access to access via plt.
102 if (M.getRtLibUseGOT() && !GV)
103 return false;
104
105 // According to the llvm language reference, we should be able to
106 // just return false in here if we have a GV, as we know it is
107 // dso_preemptable. At this point in time, the various IR producers
108 // have not been transitioned to always produce a dso_local when it
109 // is possible to do so.
110 // In the case of intrinsics, GV is null and there is nowhere to put
111 // dso_local. Returning false for those will produce worse code in some
112 // architectures. For example, on x86 the caller has to set ebx before calling
113 // a plt.
114 // As a result we still have some logic in here to improve the quality of the
115 // generated code.
116 // FIXME: Add a module level metadata for whether intrinsics should be assumed
117 // local.
118
119 Reloc::Model RM = getRelocationModel();
120 const Triple &TT = getTargetTriple();
121
122 // DLLImport explicitly marks the GV as external.
123 if (GV && GV->hasDLLImportStorageClass())
124 return false;
125
126 // On MinGW, variables that haven't been declared with DLLImport may still
127 // end up automatically imported by the linker. To make this feasible,
128 // don't assume the variables to be DSO local unless we actually know
129 // that for sure. This only has to be done for variables; for functions
130 // the linker can insert thunks for calling functions from another DLL.
131 if (TT.isWindowsGNUEnvironment() && TT.isOSBinFormatCOFF() && GV &&
132 GV->isDeclarationForLinker() && isa<GlobalVariable>(GV))
133 return false;
134
135 // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
136 // remain unresolved in the link, they can be resolved to zero, which is
137 // outside the current DSO.
138 if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
139 return false;
140
141 // Every other GV is local on COFF.
142 // Make an exception for windows OS in the triple: Some firmware builds use
143 // *-win32-macho triples. This (accidentally?) produced windows relocations
144 // without GOT tables in older clang versions; Keep this behaviour.
145 // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables
146 // either.
147 if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
148 return true;
149
150 // Most PIC code sequences that assume that a symbol is local cannot
151 // produce a 0 if it turns out the symbol is undefined. While this
152 // is ABI and relocation depended, it seems worth it to handle it
153 // here.
154 if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
155 return false;
156
157 if (GV && !GV->hasDefaultVisibility())
158 return true;
159
160 if (TT.isOSBinFormatMachO()) {
161 if (RM == Reloc::Static)
162 return true;
163 return GV && GV->isStrongDefinitionForLinker();
164 }
165
166 // Due to the AIX linkage model, any global with default visibility is
167 // considered non-local.
168 if (TT.isOSBinFormatXCOFF())
169 return false;
170
171 assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm());
172 assert(RM != Reloc::DynamicNoPIC);
173
174 bool IsExecutable =
175 RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
176 if (IsExecutable) {
177 // If the symbol is defined, it cannot be preempted.
178 if (GV && !GV->isDeclarationForLinker())
179 return true;
180
181 // A symbol marked nonlazybind should not be accessed with a plt. If the
182 // symbol turns out to be external, the linker will convert a direct
183 // access to an access via the plt, so don't assume it is local.
184 const Function *F = dyn_cast_or_null<Function>(GV);
185 if (F && F->hasFnAttribute(Attribute::NonLazyBind))
186 return false;
187 Triple::ArchType Arch = TT.getArch();
188
189 // PowerPC prefers avoiding copy relocations.
190 if (Arch == Triple::ppc || TT.isPPC64())
191 return false;
192
193 // Check if we can use copy relocations.
194 if (!(GV && GV->isThreadLocal()) && RM == Reloc::Static)
195 return true;
196 } else if (TT.isOSBinFormatELF()) {
197 // If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
198 // alias, set the flag. We cannot set dso_local for other global values,
199 // because otherwise direct accesses to a probably interposable symbol (even
200 // if the codegen assumes not) will be rejected by the linker.
201 if (!GV || !GV->canBenefitFromLocalAlias())
202 return false;
203 return TT.isX86() && M.noSemanticInterposition();
204 }
205
206 // ELF & wasm support preemption of other symbols.
207 return false;
208 }
209
useEmulatedTLS() const210 bool TargetMachine::useEmulatedTLS() const {
211 // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
212 // was specified explicitly; otherwise uses target triple to decide default.
213 if (Options.ExplicitEmulatedTLS)
214 return Options.EmulatedTLS;
215 return getTargetTriple().hasDefaultEmulatedTLS();
216 }
217
getTLSModel(const GlobalValue * GV) const218 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
219 bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
220 Reloc::Model RM = getRelocationModel();
221 bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
222 bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
223
224 TLSModel::Model Model;
225 if (IsSharedLibrary) {
226 if (IsLocal)
227 Model = TLSModel::LocalDynamic;
228 else
229 Model = TLSModel::GeneralDynamic;
230 } else {
231 if (IsLocal)
232 Model = TLSModel::LocalExec;
233 else
234 Model = TLSModel::InitialExec;
235 }
236
237 // If the user specified a more specific model, use that.
238 TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
239 if (SelectedModel > Model)
240 return SelectedModel;
241
242 return Model;
243 }
244
245 /// Returns the optimization level: None, Less, Default, or Aggressive.
getOptLevel() const246 CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
247
setOptLevel(CodeGenOpt::Level Level)248 void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
249
getTargetTransformInfo(const Function & F)250 TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
251 return TargetTransformInfo(F.getParent()->getDataLayout());
252 }
253
getNameWithPrefix(SmallVectorImpl<char> & Name,const GlobalValue * GV,Mangler & Mang,bool MayAlwaysUsePrivate) const254 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
255 const GlobalValue *GV, Mangler &Mang,
256 bool MayAlwaysUsePrivate) const {
257 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
258 // Simple case: If GV is not private, it is not important to find out if
259 // private labels are legal in this case or not.
260 Mang.getNameWithPrefix(Name, GV, false);
261 return;
262 }
263 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
264 TLOF->getNameWithPrefix(Name, GV, *this);
265 }
266
getSymbol(const GlobalValue * GV) const267 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
268 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
269 // XCOFF symbols could have special naming convention.
270 if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
271 return TargetSymbol;
272
273 SmallString<128> NameStr;
274 getNameWithPrefix(NameStr, GV, TLOF->getMangler());
275 return TLOF->getContext().getOrCreateSymbol(NameStr);
276 }
277
getTargetIRAnalysis()278 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
279 // Since Analysis can't depend on Target, use a std::function to invert the
280 // dependency.
281 return TargetIRAnalysis(
282 [this](const Function &F) { return this->getTargetTransformInfo(F); });
283 }
284