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/GlobalValue.h"
17 #include "llvm/IR/GlobalVariable.h"
18 #include "llvm/IR/Mangler.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCInstrInfo.h"
23 #include "llvm/MC/MCRegisterInfo.h"
24 #include "llvm/MC/MCSubtargetInfo.h"
25 #include "llvm/Support/CodeGen.h"
26 #include "llvm/Target/TargetLoweringObjectFile.h"
27 using namespace llvm;
28
29 //---------------------------------------------------------------------------
30 // TargetMachine Class
31 //
32
TargetMachine(const Target & T,StringRef DataLayoutString,const Triple & TT,StringRef CPU,StringRef FS,const TargetOptions & Options)33 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
34 const Triple &TT, StringRef CPU, StringRef FS,
35 const TargetOptions &Options)
36 : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
37 TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
38 MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
39 O0WantsFastISel(false), Options(Options) {}
40
41 TargetMachine::~TargetMachine() = default;
42
isLargeGlobalValue(const GlobalValue * GVal) const43 bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
44 if (getTargetTriple().getArch() != Triple::x86_64)
45 return false;
46
47 // Remaining logic below is ELF-specific. For other object file formats where
48 // the large code model is mostly used for JIT compilation, just look at the
49 // code model.
50 if (!getTargetTriple().isOSBinFormatELF())
51 return getCodeModel() == CodeModel::Large;
52
53 auto *GO = GVal->getAliaseeObject();
54
55 // Be conservative if we can't find an underlying GlobalObject.
56 if (!GO)
57 return true;
58
59 auto *GV = dyn_cast<GlobalVariable>(GO);
60
61 auto IsPrefix = [](StringRef Name, StringRef Prefix) {
62 return Name.consume_front(Prefix) && (Name.empty() || Name[0] == '.');
63 };
64
65 // Functions/GlobalIFuncs are only large under the large code model.
66 if (!GV) {
67 // Handle explicit sections as we do for GlobalVariables with an explicit
68 // section, see comments below.
69 if (GO->hasSection()) {
70 StringRef Name = GO->getSection();
71 return IsPrefix(Name, ".ltext");
72 }
73 return getCodeModel() == CodeModel::Large;
74 }
75
76 if (GV->isThreadLocal())
77 return false;
78
79 // For x86-64, we treat an explicit GlobalVariable small code model to mean
80 // that the global should be placed in a small section, and ditto for large.
81 if (auto CM = GV->getCodeModel()) {
82 if (*CM == CodeModel::Small)
83 return false;
84 if (*CM == CodeModel::Large)
85 return true;
86 }
87
88 // Treat all globals in explicit sections as small, except for the standard
89 // large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
90 // together small and large sections, resulting in small references to large
91 // data sections. The code model attribute overrides this above.
92 if (GV->hasSection()) {
93 StringRef Name = GV->getSection();
94 return IsPrefix(Name, ".lbss") || IsPrefix(Name, ".ldata") ||
95 IsPrefix(Name, ".lrodata");
96 }
97
98 // Respect large data threshold for medium and large code models.
99 if (getCodeModel() == CodeModel::Medium ||
100 getCodeModel() == CodeModel::Large) {
101 if (!GV->getValueType()->isSized())
102 return true;
103 // Linker defined start/stop symbols can point to arbitrary points in the
104 // binary, so treat them as large.
105 if (GV->isDeclaration() && (GV->getName() == "__ehdr_start" ||
106 GV->getName().starts_with("__start_") ||
107 GV->getName().starts_with("__stop_")))
108 return true;
109 const DataLayout &DL = GV->getDataLayout();
110 uint64_t Size = DL.getTypeAllocSize(GV->getValueType());
111 return Size == 0 || Size > LargeDataThreshold;
112 }
113
114 return false;
115 }
116
isPositionIndependent() const117 bool TargetMachine::isPositionIndependent() const {
118 return getRelocationModel() == Reloc::PIC_;
119 }
120
121 /// Reset the target options based on the function's attributes.
122 /// setFunctionAttributes should have made the raw attribute value consistent
123 /// with the command line flag if used.
124 //
125 // FIXME: This function needs to go away for a number of reasons:
126 // a) global state on the TargetMachine is terrible in general,
127 // b) these target options should be passed only on the function
128 // and not on the TargetMachine (via TargetOptions) at all.
resetTargetOptions(const Function & F) const129 void TargetMachine::resetTargetOptions(const Function &F) const {
130 #define RESET_OPTION(X, Y) \
131 do { \
132 Options.X = F.getFnAttribute(Y).getValueAsBool(); \
133 } while (0)
134
135 RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
136 RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
137 RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
138 RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
139 RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
140 }
141
142 /// Returns the code generation relocation model. The choices are static, PIC,
143 /// and dynamic-no-pic.
getRelocationModel() const144 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
145
getMaxCodeSize() const146 uint64_t TargetMachine::getMaxCodeSize() const {
147 switch (getCodeModel()) {
148 case CodeModel::Tiny:
149 return llvm::maxUIntN(10);
150 case CodeModel::Small:
151 case CodeModel::Kernel:
152 case CodeModel::Medium:
153 return llvm::maxUIntN(31);
154 case CodeModel::Large:
155 return llvm::maxUIntN(64);
156 }
157 llvm_unreachable("Unhandled CodeModel enum");
158 }
159
160 /// Get the IR-specified TLS model for Var.
getSelectedTLSModel(const GlobalValue * GV)161 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
162 switch (GV->getThreadLocalMode()) {
163 case GlobalVariable::NotThreadLocal:
164 llvm_unreachable("getSelectedTLSModel for non-TLS variable");
165 break;
166 case GlobalVariable::GeneralDynamicTLSModel:
167 return TLSModel::GeneralDynamic;
168 case GlobalVariable::LocalDynamicTLSModel:
169 return TLSModel::LocalDynamic;
170 case GlobalVariable::InitialExecTLSModel:
171 return TLSModel::InitialExec;
172 case GlobalVariable::LocalExecTLSModel:
173 return TLSModel::LocalExec;
174 }
175 llvm_unreachable("invalid TLS model");
176 }
177
shouldAssumeDSOLocal(const GlobalValue * GV) const178 bool TargetMachine::shouldAssumeDSOLocal(const GlobalValue *GV) const {
179 const Triple &TT = getTargetTriple();
180 Reloc::Model RM = getRelocationModel();
181
182 // According to the llvm language reference, we should be able to
183 // just return false in here if we have a GV, as we know it is
184 // dso_preemptable. At this point in time, the various IR producers
185 // have not been transitioned to always produce a dso_local when it
186 // is possible to do so.
187 //
188 // As a result we still have some logic in here to improve the quality of the
189 // generated code.
190 if (!GV)
191 return false;
192
193 // If the IR producer requested that this GV be treated as dso local, obey.
194 if (GV->isDSOLocal())
195 return true;
196
197 if (TT.isOSBinFormatCOFF()) {
198 // DLLImport explicitly marks the GV as external.
199 if (GV->hasDLLImportStorageClass())
200 return false;
201
202 // On MinGW, variables that haven't been declared with DLLImport may still
203 // end up automatically imported by the linker. To make this feasible,
204 // don't assume the variables to be DSO local unless we actually know
205 // that for sure. This only has to be done for variables; for functions
206 // the linker can insert thunks for calling functions from another DLL.
207 if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
208 isa<GlobalVariable>(GV))
209 return false;
210
211 // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
212 // unresolved in the link, they can be resolved to zero, which is outside
213 // the current DSO.
214 if (GV->hasExternalWeakLinkage())
215 return false;
216
217 // Every other GV is local on COFF.
218 return true;
219 }
220
221 if (TT.isOSBinFormatGOFF())
222 return true;
223
224 if (TT.isOSBinFormatMachO()) {
225 if (RM == Reloc::Static)
226 return true;
227 return GV->isStrongDefinitionForLinker();
228 }
229
230 assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
231 TT.isOSBinFormatXCOFF());
232 return false;
233 }
234
useEmulatedTLS() const235 bool TargetMachine::useEmulatedTLS() const { return Options.EmulatedTLS; }
useTLSDESC() const236 bool TargetMachine::useTLSDESC() const { return Options.EnableTLSDESC; }
237
getTLSModel(const GlobalValue * GV) const238 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
239 bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
240 Reloc::Model RM = getRelocationModel();
241 bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
242 bool IsLocal = shouldAssumeDSOLocal(GV);
243
244 TLSModel::Model Model;
245 if (IsSharedLibrary) {
246 if (IsLocal)
247 Model = TLSModel::LocalDynamic;
248 else
249 Model = TLSModel::GeneralDynamic;
250 } else {
251 if (IsLocal)
252 Model = TLSModel::LocalExec;
253 else
254 Model = TLSModel::InitialExec;
255 }
256
257 // If the user specified a more specific model, use that.
258 TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
259 if (SelectedModel > Model)
260 return SelectedModel;
261
262 return Model;
263 }
264
265 /// Returns the optimization level: None, Less, Default, or Aggressive.
getOptLevel() const266 CodeGenOptLevel TargetMachine::getOptLevel() const { return OptLevel; }
267
setOptLevel(CodeGenOptLevel Level)268 void TargetMachine::setOptLevel(CodeGenOptLevel Level) { OptLevel = Level; }
269
270 TargetTransformInfo
getTargetTransformInfo(const Function & F) const271 TargetMachine::getTargetTransformInfo(const Function &F) const {
272 return TargetTransformInfo(F.getDataLayout());
273 }
274
getNameWithPrefix(SmallVectorImpl<char> & Name,const GlobalValue * GV,Mangler & Mang,bool MayAlwaysUsePrivate) const275 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
276 const GlobalValue *GV, Mangler &Mang,
277 bool MayAlwaysUsePrivate) const {
278 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
279 // Simple case: If GV is not private, it is not important to find out if
280 // private labels are legal in this case or not.
281 Mang.getNameWithPrefix(Name, GV, false);
282 return;
283 }
284 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
285 TLOF->getNameWithPrefix(Name, GV, *this);
286 }
287
getSymbol(const GlobalValue * GV) const288 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
289 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
290 // XCOFF symbols could have special naming convention.
291 if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
292 return TargetSymbol;
293
294 SmallString<128> NameStr;
295 getNameWithPrefix(NameStr, GV, TLOF->getMangler());
296 return TLOF->getContext().getOrCreateSymbol(NameStr);
297 }
298
getTargetIRAnalysis() const299 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
300 // Since Analysis can't depend on Target, use a std::function to invert the
301 // dependency.
302 return TargetIRAnalysis(
303 [this](const Function &F) { return this->getTargetTransformInfo(F); });
304 }
305
parseBinutilsVersion(StringRef Version)306 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
307 if (Version == "none")
308 return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
309 std::pair<int, int> Ret;
310 if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
311 Version.consumeInteger(10, Ret.second);
312 return Ret;
313 }
314