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/MC/MCAsmInfo.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCInstrInfo.h"
22 #include "llvm/MC/MCRegisterInfo.h"
23 #include "llvm/MC/MCSubtargetInfo.h"
24 #include "llvm/Support/CodeGen.h"
25 #include "llvm/Target/TargetLoweringObjectFile.h"
26 using namespace llvm;
27
28 //---------------------------------------------------------------------------
29 // TargetMachine Class
30 //
31
TargetMachine(const Target & T,StringRef DataLayoutString,const Triple & TT,StringRef CPU,StringRef FS,const TargetOptions & Options)32 TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
33 const Triple &TT, StringRef CPU, StringRef FS,
34 const TargetOptions &Options)
35 : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
36 TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
37 MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
38 O0WantsFastISel(false), Options(Options) {}
39
40 TargetMachine::~TargetMachine() = default;
41
isLargeGlobalValue(const GlobalValue * GVal) const42 bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
43 if (getTargetTriple().getArch() != Triple::x86_64)
44 return false;
45
46 auto *GO = GVal->getAliaseeObject();
47
48 // Be conservative if we can't find an underlying GlobalObject.
49 if (!GO)
50 return true;
51
52 auto *GV = dyn_cast<GlobalVariable>(GO);
53
54 // Functions/GlobalIFuncs are only large under the large code model.
55 if (!GV)
56 return getCodeModel() == CodeModel::Large;
57
58 if (GV->isThreadLocal())
59 return false;
60
61 // For x86-64, we treat an explicit GlobalVariable small code model to mean
62 // that the global should be placed in a small section, and ditto for large.
63 if (auto CM = GV->getCodeModel()) {
64 if (*CM == CodeModel::Small)
65 return false;
66 if (*CM == CodeModel::Large)
67 return true;
68 }
69
70 // Treat all globals in explicit sections as small, except for the standard
71 // large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
72 // together small and large sections, resulting in small references to large
73 // data sections. The code model attribute overrides this above.
74 if (GV->hasSection()) {
75 StringRef Name = GV->getSection();
76 auto IsPrefix = [&](StringRef Prefix) {
77 StringRef S = Name;
78 return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
79 };
80 return IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata");
81 }
82
83 // Respect large data threshold for medium and large code models.
84 if (getCodeModel() == CodeModel::Medium ||
85 getCodeModel() == CodeModel::Large) {
86 if (!GV->getValueType()->isSized())
87 return true;
88 const DataLayout &DL = GV->getParent()->getDataLayout();
89 uint64_t Size = DL.getTypeSizeInBits(GV->getValueType()) / 8;
90 return Size == 0 || Size > LargeDataThreshold;
91 }
92
93 return false;
94 }
95
isPositionIndependent() const96 bool TargetMachine::isPositionIndependent() const {
97 return getRelocationModel() == Reloc::PIC_;
98 }
99
100 /// Reset the target options based on the function's attributes.
101 /// setFunctionAttributes should have made the raw attribute value consistent
102 /// with the command line flag if used.
103 //
104 // FIXME: This function needs to go away for a number of reasons:
105 // a) global state on the TargetMachine is terrible in general,
106 // b) these target options should be passed only on the function
107 // and not on the TargetMachine (via TargetOptions) at all.
resetTargetOptions(const Function & F) const108 void TargetMachine::resetTargetOptions(const Function &F) const {
109 #define RESET_OPTION(X, Y) \
110 do { \
111 Options.X = F.getFnAttribute(Y).getValueAsBool(); \
112 } while (0)
113
114 RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
115 RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
116 RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
117 RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
118 RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
119 }
120
121 /// Returns the code generation relocation model. The choices are static, PIC,
122 /// and dynamic-no-pic.
getRelocationModel() const123 Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
124
getMaxCodeSize() const125 uint64_t TargetMachine::getMaxCodeSize() const {
126 switch (getCodeModel()) {
127 case CodeModel::Tiny:
128 return llvm::maxUIntN(10);
129 case CodeModel::Small:
130 case CodeModel::Kernel:
131 case CodeModel::Medium:
132 return llvm::maxUIntN(31);
133 case CodeModel::Large:
134 return llvm::maxUIntN(64);
135 }
136 llvm_unreachable("Unhandled CodeModel enum");
137 }
138
139 /// Get the IR-specified TLS model for Var.
getSelectedTLSModel(const GlobalValue * GV)140 static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
141 switch (GV->getThreadLocalMode()) {
142 case GlobalVariable::NotThreadLocal:
143 llvm_unreachable("getSelectedTLSModel for non-TLS variable");
144 break;
145 case GlobalVariable::GeneralDynamicTLSModel:
146 return TLSModel::GeneralDynamic;
147 case GlobalVariable::LocalDynamicTLSModel:
148 return TLSModel::LocalDynamic;
149 case GlobalVariable::InitialExecTLSModel:
150 return TLSModel::InitialExec;
151 case GlobalVariable::LocalExecTLSModel:
152 return TLSModel::LocalExec;
153 }
154 llvm_unreachable("invalid TLS model");
155 }
156
shouldAssumeDSOLocal(const Module & M,const GlobalValue * GV) const157 bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
158 const GlobalValue *GV) const {
159 const Triple &TT = getTargetTriple();
160 Reloc::Model RM = getRelocationModel();
161
162 // According to the llvm language reference, we should be able to
163 // just return false in here if we have a GV, as we know it is
164 // dso_preemptable. At this point in time, the various IR producers
165 // have not been transitioned to always produce a dso_local when it
166 // is possible to do so.
167 //
168 // As a result we still have some logic in here to improve the quality of the
169 // generated code.
170 if (!GV)
171 return false;
172
173 // If the IR producer requested that this GV be treated as dso local, obey.
174 if (GV->isDSOLocal())
175 return true;
176
177 if (TT.isOSBinFormatCOFF()) {
178 // DLLImport explicitly marks the GV as external.
179 if (GV->hasDLLImportStorageClass())
180 return false;
181
182 // On MinGW, variables that haven't been declared with DLLImport may still
183 // end up automatically imported by the linker. To make this feasible,
184 // don't assume the variables to be DSO local unless we actually know
185 // that for sure. This only has to be done for variables; for functions
186 // the linker can insert thunks for calling functions from another DLL.
187 if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
188 isa<GlobalVariable>(GV))
189 return false;
190
191 // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
192 // unresolved in the link, they can be resolved to zero, which is outside
193 // the current DSO.
194 if (GV->hasExternalWeakLinkage())
195 return false;
196
197 // Every other GV is local on COFF.
198 return true;
199 }
200
201 if (TT.isOSBinFormatGOFF())
202 return true;
203
204 if (TT.isOSBinFormatMachO()) {
205 if (RM == Reloc::Static)
206 return true;
207 return GV->isStrongDefinitionForLinker();
208 }
209
210 assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
211 TT.isOSBinFormatXCOFF());
212 return false;
213 }
214
useEmulatedTLS() const215 bool TargetMachine::useEmulatedTLS() const { return Options.EmulatedTLS; }
useTLSDESC() const216 bool TargetMachine::useTLSDESC() const { return Options.EnableTLSDESC; }
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 CodeGenOptLevel TargetMachine::getOptLevel() const { return OptLevel; }
247
setOptLevel(CodeGenOptLevel Level)248 void TargetMachine::setOptLevel(CodeGenOptLevel Level) { OptLevel = Level; }
249
250 TargetTransformInfo
getTargetTransformInfo(const Function & F) const251 TargetMachine::getTargetTransformInfo(const Function &F) const {
252 return TargetTransformInfo(F.getParent()->getDataLayout());
253 }
254
getNameWithPrefix(SmallVectorImpl<char> & Name,const GlobalValue * GV,Mangler & Mang,bool MayAlwaysUsePrivate) const255 void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
256 const GlobalValue *GV, Mangler &Mang,
257 bool MayAlwaysUsePrivate) const {
258 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
259 // Simple case: If GV is not private, it is not important to find out if
260 // private labels are legal in this case or not.
261 Mang.getNameWithPrefix(Name, GV, false);
262 return;
263 }
264 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
265 TLOF->getNameWithPrefix(Name, GV, *this);
266 }
267
getSymbol(const GlobalValue * GV) const268 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
269 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
270 // XCOFF symbols could have special naming convention.
271 if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
272 return TargetSymbol;
273
274 SmallString<128> NameStr;
275 getNameWithPrefix(NameStr, GV, TLOF->getMangler());
276 return TLOF->getContext().getOrCreateSymbol(NameStr);
277 }
278
getTargetIRAnalysis() const279 TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
280 // Since Analysis can't depend on Target, use a std::function to invert the
281 // dependency.
282 return TargetIRAnalysis(
283 [this](const Function &F) { return this->getTargetTransformInfo(F); });
284 }
285
parseBinutilsVersion(StringRef Version)286 std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
287 if (Version == "none")
288 return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
289 std::pair<int, int> Ret;
290 if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
291 Version.consumeInteger(10, Ret.second);
292 return Ret;
293 }
294