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/MCStreamer.h"
25#include "llvm/MC/MCSubtargetInfo.h"
26#include "llvm/Support/CodeGen.h"
27#include "llvm/Target/TargetLoweringObjectFile.h"
28using namespace llvm;
29
30cl::opt<bool> NoKernelInfoEndLTO(
31 "no-kernel-info-end-lto",
32 cl::desc("remove the kernel-info pass at the end of the full LTO pipeline"),
33 cl::init(Val: false), cl::Hidden);
34
35//---------------------------------------------------------------------------
36// TargetMachine Class
37//
38
39TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
40 const Triple &TT, StringRef CPU, StringRef FS,
41 const TargetOptions &Options)
42 : TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
43 TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
44 MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
45 O0WantsFastISel(false), Options(Options) {}
46
47TargetMachine::~TargetMachine() = default;
48
49Expected<std::unique_ptr<MCStreamer>>
50TargetMachine::createMCStreamer(raw_pwrite_stream &Out,
51 raw_pwrite_stream *DwoOut,
52 CodeGenFileType FileType, MCContext &Ctx) {
53 return nullptr;
54}
55
56bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
57 if (getTargetTriple().getArch() != Triple::x86_64)
58 return false;
59
60 // Remaining logic below is ELF-specific. For other object file formats where
61 // the large code model is mostly used for JIT compilation, just look at the
62 // code model.
63 if (!getTargetTriple().isOSBinFormatELF())
64 return getCodeModel() == CodeModel::Large;
65
66 auto *GO = GVal->getAliaseeObject();
67
68 // Be conservative if we can't find an underlying GlobalObject.
69 if (!GO)
70 return true;
71
72 auto *GV = dyn_cast<GlobalVariable>(Val: GO);
73
74 auto IsPrefix = [](StringRef Name, StringRef Prefix) {
75 return Name.consume_front(Prefix) && (Name.empty() || Name[0] == '.');
76 };
77
78 // Functions/GlobalIFuncs are only large under the large code model.
79 if (!GV) {
80 // Handle explicit sections as we do for GlobalVariables with an explicit
81 // section, see comments below.
82 if (GO->hasSection()) {
83 StringRef Name = GO->getSection();
84 return IsPrefix(Name, ".ltext");
85 }
86 return getCodeModel() == CodeModel::Large;
87 }
88
89 if (GV->isThreadLocal())
90 return false;
91
92 // For x86-64, we treat an explicit GlobalVariable small code model to mean
93 // that the global should be placed in a small section, and ditto for large.
94 if (auto CM = GV->getCodeModel()) {
95 if (*CM == CodeModel::Small)
96 return false;
97 if (*CM == CodeModel::Large)
98 return true;
99 }
100
101 // Treat all globals in explicit sections as small, except for the standard
102 // large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
103 // together small and large sections, resulting in small references to large
104 // data sections. The code model attribute overrides this above.
105 if (GV->hasSection()) {
106 StringRef Name = GV->getSection();
107 return IsPrefix(Name, ".lbss") || IsPrefix(Name, ".ldata") ||
108 IsPrefix(Name, ".lrodata");
109 }
110
111 // Respect large data threshold for medium and large code models.
112 if (getCodeModel() == CodeModel::Medium ||
113 getCodeModel() == CodeModel::Large) {
114 if (!GV->getValueType()->isSized())
115 return true;
116 // Linker defined start/stop symbols can point to arbitrary points in the
117 // binary, so treat them as large.
118 if (GV->isDeclaration() && (GV->getName() == "__ehdr_start" ||
119 GV->getName().starts_with(Prefix: "__start_") ||
120 GV->getName().starts_with(Prefix: "__stop_")))
121 return true;
122 // Linkers do not currently support PT_GNU_RELRO for SHF_X86_64_LARGE
123 // sections; that would require the linker to emit more than one
124 // PT_GNU_RELRO because large sections are discontiguous by design, and most
125 // ELF dynamic loaders do not support that (bionic appears to support it but
126 // glibc/musl/FreeBSD/NetBSD/OpenBSD appear not to). With current linkers
127 // these sections will end up in .ldata which results in silently disabling
128 // RELRO. If this ever gets supported by downstream components in the future
129 // we could add an opt-in flag for moving these sections to .ldata.rel.ro
130 // which would trigger the creation of a second PT_GNU_RELRO.
131 if (!GV->isDeclarationForLinker() &&
132 TargetLoweringObjectFile::getKindForGlobal(GO: GV, TM: *this)
133 .isReadOnlyWithRel())
134 return false;
135 const DataLayout &DL = GV->getDataLayout();
136 uint64_t Size = DL.getTypeAllocSize(Ty: GV->getValueType());
137 return Size == 0 || Size > LargeDataThreshold;
138 }
139
140 return false;
141}
142
143bool TargetMachine::isPositionIndependent() const {
144 return getRelocationModel() == Reloc::PIC_;
145}
146
147/// Reset the target options based on the function's attributes.
148/// setFunctionAttributes should have made the raw attribute value consistent
149/// with the command line flag if used.
150//
151// FIXME: This function needs to go away for a number of reasons:
152// a) global state on the TargetMachine is terrible in general,
153// b) these target options should be passed only on the function
154// and not on the TargetMachine (via TargetOptions) at all.
155void TargetMachine::resetTargetOptions(const Function &F) const {
156#define RESET_OPTION(X, Y) \
157 do { \
158 Options.X = F.getFnAttribute(Y).getValueAsBool(); \
159 } while (0)
160
161 RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
162 RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
163 RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
164 RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
165 RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
166}
167
168/// Returns the code generation relocation model. The choices are static, PIC,
169/// and dynamic-no-pic.
170Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
171
172uint64_t TargetMachine::getMaxCodeSize() const {
173 switch (getCodeModel()) {
174 case CodeModel::Tiny:
175 return llvm::maxUIntN(N: 10);
176 case CodeModel::Small:
177 case CodeModel::Kernel:
178 case CodeModel::Medium:
179 return llvm::maxUIntN(N: 31);
180 case CodeModel::Large:
181 return llvm::maxUIntN(N: 64);
182 }
183 llvm_unreachable("Unhandled CodeModel enum");
184}
185
186/// Get the IR-specified TLS model for Var.
187static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
188 switch (GV->getThreadLocalMode()) {
189 case GlobalVariable::NotThreadLocal:
190 llvm_unreachable("getSelectedTLSModel for non-TLS variable");
191 break;
192 case GlobalVariable::GeneralDynamicTLSModel:
193 return TLSModel::GeneralDynamic;
194 case GlobalVariable::LocalDynamicTLSModel:
195 return TLSModel::LocalDynamic;
196 case GlobalVariable::InitialExecTLSModel:
197 return TLSModel::InitialExec;
198 case GlobalVariable::LocalExecTLSModel:
199 return TLSModel::LocalExec;
200 }
201 llvm_unreachable("invalid TLS model");
202}
203
204bool TargetMachine::shouldAssumeDSOLocal(const GlobalValue *GV) const {
205 const Triple &TT = getTargetTriple();
206 Reloc::Model RM = getRelocationModel();
207
208 // According to the llvm language reference, we should be able to
209 // just return false in here if we have a GV, as we know it is
210 // dso_preemptable. At this point in time, the various IR producers
211 // have not been transitioned to always produce a dso_local when it
212 // is possible to do so.
213 //
214 // As a result we still have some logic in here to improve the quality of the
215 // generated code.
216 if (!GV)
217 return false;
218
219 // If the IR producer requested that this GV be treated as dso local, obey.
220 if (GV->isDSOLocal())
221 return true;
222
223 if (TT.isOSBinFormatCOFF()) {
224 // DLLImport explicitly marks the GV as external.
225 if (GV->hasDLLImportStorageClass())
226 return false;
227
228 // On MinGW, variables that haven't been declared with DLLImport may still
229 // end up automatically imported by the linker. To make this feasible,
230 // don't assume the variables to be DSO local unless we actually know
231 // that for sure. This only has to be done for variables; for functions
232 // the linker can insert thunks for calling functions from another DLL.
233 if (TT.isOSCygMing() && GV->isDeclarationForLinker() &&
234 isa<GlobalVariable>(Val: GV))
235 return false;
236
237 // Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
238 // unresolved in the link, they can be resolved to zero, which is outside
239 // the current DSO.
240 if (GV->hasExternalWeakLinkage())
241 return false;
242
243 // Every other GV is local on COFF.
244 return true;
245 }
246
247 if (TT.isOSBinFormatGOFF())
248 return true;
249
250 if (TT.isOSBinFormatMachO()) {
251 if (RM == Reloc::Static)
252 return true;
253 return GV->isStrongDefinitionForLinker();
254 }
255
256 assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
257 TT.isOSBinFormatXCOFF());
258 return false;
259}
260
261bool TargetMachine::useEmulatedTLS() const { return Options.EmulatedTLS; }
262bool TargetMachine::useTLSDESC() const { return Options.EnableTLSDESC; }
263
264TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
265 bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
266 Reloc::Model RM = getRelocationModel();
267 bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
268 bool IsLocal = shouldAssumeDSOLocal(GV);
269
270 TLSModel::Model Model;
271 if (IsSharedLibrary) {
272 if (IsLocal)
273 Model = TLSModel::LocalDynamic;
274 else
275 Model = TLSModel::GeneralDynamic;
276 } else {
277 if (IsLocal)
278 Model = TLSModel::LocalExec;
279 else
280 Model = TLSModel::InitialExec;
281 }
282
283 // If the user specified a more specific model, use that.
284 TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
285 if (SelectedModel > Model)
286 return SelectedModel;
287
288 return Model;
289}
290
291TargetTransformInfo
292TargetMachine::getTargetTransformInfo(const Function &F) const {
293 return TargetTransformInfo(F.getDataLayout());
294}
295
296void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
297 const GlobalValue *GV, Mangler &Mang,
298 bool MayAlwaysUsePrivate) const {
299 if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
300 // Simple case: If GV is not private, it is not important to find out if
301 // private labels are legal in this case or not.
302 Mang.getNameWithPrefix(OutName&: Name, GV, CannotUsePrivateLabel: false);
303 return;
304 }
305 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
306 TLOF->getNameWithPrefix(OutName&: Name, GV, TM: *this);
307}
308
309MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
310 const TargetLoweringObjectFile *TLOF = getObjFileLowering();
311 // XCOFF symbols could have special naming convention.
312 if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, TM: *this))
313 return TargetSymbol;
314
315 SmallString<128> NameStr;
316 getNameWithPrefix(Name&: NameStr, GV, Mang&: TLOF->getMangler());
317 return TLOF->getContext().getOrCreateSymbol(Name: NameStr);
318}
319
320TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
321 // Since Analysis can't depend on Target, use a std::function to invert the
322 // dependency.
323 return TargetIRAnalysis(
324 [this](const Function &F) { return this->getTargetTransformInfo(F); });
325}
326
327std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
328 if (Version == "none")
329 return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
330 std::pair<int, int> Ret;
331 if (!Version.consumeInteger(Radix: 10, Result&: Ret.first) && Version.consume_front(Prefix: "."))
332 Version.consumeInteger(Radix: 10, Result&: Ret.second);
333 return Ret;
334}
335