1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains the declarations of the HexagonTargetAsmInfo properties.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #define DEBUG_TYPE "hexagon-sdata"
15
16 #include "HexagonTargetObjectFile.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/BinaryFormat/ELF.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/DerivedTypes.h"
23 #include "llvm/IR/GlobalObject.h"
24 #include "llvm/IR/GlobalValue.h"
25 #include "llvm/IR/GlobalVariable.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/MC/MCContext.h"
28 #include "llvm/MC/SectionKind.h"
29 #include "llvm/Support/Casting.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/Target/TargetMachine.h"
34
35 using namespace llvm;
36
37 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
38 cl::init(8), cl::Hidden,
39 cl::desc("The maximum size of an object in the sdata section"));
40
41 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
42 cl::Hidden, cl::desc("Disable small data sections sorting"));
43
44 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
45 cl::init(false), cl::Hidden, cl::ZeroOrMore,
46 cl::desc("Allow static variables in .sdata"));
47
48 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
49 cl::Hidden, cl::init(false),
50 cl::desc("Trace global value placement"));
51
52 static cl::opt<bool>
53 EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
54 cl::desc("Emit hexagon jump tables in function section"));
55
56 static cl::opt<bool>
57 EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
58 cl::desc("Emit hexagon lookup tables in function section"));
59
60 // TraceGVPlacement controls messages for all builds. For builds with assertions
61 // (debug or release), messages are also controlled by the usual debug flags
62 // (e.g. -debug and -debug-only=globallayout)
63 #define TRACE_TO(s, X) s << X
64 #ifdef NDEBUG
65 #define TRACE(X) \
66 do { \
67 if (TraceGVPlacement) { \
68 TRACE_TO(errs(), X); \
69 } \
70 } while (false)
71 #else
72 #define TRACE(X) \
73 do { \
74 if (TraceGVPlacement) { \
75 TRACE_TO(errs(), X); \
76 } else { \
77 LLVM_DEBUG(TRACE_TO(dbgs(), X)); \
78 } \
79 } while (false)
80 #endif
81
82 // Returns true if the section name is such that the symbol will be put
83 // in a small data section.
84 // For instance, global variables with section attributes such as ".sdata"
85 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
isSmallDataSection(StringRef Sec)86 static bool isSmallDataSection(StringRef Sec) {
87 // sectionName is either ".sdata" or ".sbss". Looking for an exact match
88 // obviates the need for checks for section names such as ".sdatafoo".
89 if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
90 return true;
91 // If either ".sdata." or ".sbss." is a substring of the section name
92 // then put the symbol in small data.
93 return Sec.find(".sdata.") != StringRef::npos ||
94 Sec.find(".sbss.") != StringRef::npos ||
95 Sec.find(".scommon.") != StringRef::npos;
96 }
97
getSectionSuffixForSize(unsigned Size)98 static const char *getSectionSuffixForSize(unsigned Size) {
99 switch (Size) {
100 default:
101 return "";
102 case 1:
103 return ".1";
104 case 2:
105 return ".2";
106 case 4:
107 return ".4";
108 case 8:
109 return ".8";
110 }
111 }
112
Initialize(MCContext & Ctx,const TargetMachine & TM)113 void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
114 const TargetMachine &TM) {
115 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
116 InitializeELF(TM.Options.UseInitArray);
117
118 SmallDataSection =
119 getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
120 ELF::SHF_WRITE | ELF::SHF_ALLOC |
121 ELF::SHF_HEX_GPREL);
122 SmallBSSSection =
123 getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
124 ELF::SHF_WRITE | ELF::SHF_ALLOC |
125 ELF::SHF_HEX_GPREL);
126 }
127
SelectSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const128 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
129 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
130 TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
131 TRACE("input section(" << GO->getSection() << ") ");
132
133 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
134 << (GO->hasLocalLinkage() ? "local_linkage " : "")
135 << (GO->hasInternalLinkage() ? "internal " : "")
136 << (GO->hasExternalLinkage() ? "external " : "")
137 << (GO->hasCommonLinkage() ? "common_linkage " : "")
138 << (GO->hasCommonLinkage() ? "common " : "" )
139 << (Kind.isCommon() ? "kind_common " : "" )
140 << (Kind.isBSS() ? "kind_bss " : "" )
141 << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
142
143 // If the lookup table is used by more than one function, do not place
144 // it in text section.
145 if (EmitLutInText && GO->getName().startswith("switch.table")) {
146 if (const Function *Fn = getLutUsedFunction(GO))
147 return selectSectionForLookupTable(GO, TM, Fn);
148 }
149
150 if (isGlobalInSmallSection(GO, TM))
151 return selectSmallSectionForGlobal(GO, Kind, TM);
152
153 if (Kind.isCommon()) {
154 // This is purely for LTO+Linker Script because commons don't really have a
155 // section. However, the BitcodeSectionWriter pass will query for the
156 // sections of commons (and the linker expects us to know their section) so
157 // we'll return one here.
158 return BSSSection;
159 }
160
161 TRACE("default_ELF_section\n");
162 // Otherwise, we work the same as ELF.
163 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
164 }
165
getExplicitSectionGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const166 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
167 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
168 TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
169 << GO->getSection() << ") ");
170 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
171 << (GO->hasLocalLinkage() ? "local_linkage " : "")
172 << (GO->hasInternalLinkage() ? "internal " : "")
173 << (GO->hasExternalLinkage() ? "external " : "")
174 << (GO->hasCommonLinkage() ? "common_linkage " : "")
175 << (GO->hasCommonLinkage() ? "common " : "" )
176 << (Kind.isCommon() ? "kind_common " : "" )
177 << (Kind.isBSS() ? "kind_bss " : "" )
178 << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
179
180 if (GO->hasSection()) {
181 StringRef Section = GO->getSection();
182 if (Section.find(".access.text.group") != StringRef::npos)
183 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
184 ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
185 if (Section.find(".access.data.group") != StringRef::npos)
186 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
187 ELF::SHF_WRITE | ELF::SHF_ALLOC);
188 }
189
190 if (isGlobalInSmallSection(GO, TM))
191 return selectSmallSectionForGlobal(GO, Kind, TM);
192
193 // Otherwise, we work the same as ELF.
194 TRACE("default_ELF_section\n");
195 return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
196 }
197
198 /// Return true if this global value should be placed into small data/bss
199 /// section.
isGlobalInSmallSection(const GlobalObject * GO,const TargetMachine & TM) const200 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
201 const TargetMachine &TM) const {
202 // Only global variables, not functions.
203 LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
204 << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
205 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
206 if (!GVar) {
207 LLVM_DEBUG(dbgs() << "no, not a global variable\n");
208 return false;
209 }
210
211 // Globals with external linkage that have an original section set must be
212 // emitted to that section, regardless of whether we would put them into
213 // small data or not. This is how we can support mixing -G0/-G8 in LTO.
214 if (GVar->hasSection()) {
215 bool IsSmall = isSmallDataSection(GVar->getSection());
216 LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
217 << ", has section: " << GVar->getSection() << '\n');
218 return IsSmall;
219 }
220
221 if (GVar->isConstant()) {
222 LLVM_DEBUG(dbgs() << "no, is a constant\n");
223 return false;
224 }
225
226 bool IsLocal = GVar->hasLocalLinkage();
227 if (!StaticsInSData && IsLocal) {
228 LLVM_DEBUG(dbgs() << "no, is static\n");
229 return false;
230 }
231
232 Type *GType = GVar->getType();
233 if (PointerType *PT = dyn_cast<PointerType>(GType))
234 GType = PT->getElementType();
235
236 if (isa<ArrayType>(GType)) {
237 LLVM_DEBUG(dbgs() << "no, is an array\n");
238 return false;
239 }
240
241 // If the type is a struct with no body provided, treat is conservatively.
242 // There cannot be actual definitions of object of such a type in this CU
243 // (only references), so assuming that they are not in sdata is safe. If
244 // these objects end up in the sdata, the references will still be valid.
245 if (StructType *ST = dyn_cast<StructType>(GType)) {
246 if (ST->isOpaque()) {
247 LLVM_DEBUG(dbgs() << "no, has opaque type\n");
248 return false;
249 }
250 }
251
252 unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
253 if (Size == 0) {
254 LLVM_DEBUG(dbgs() << "no, has size 0\n");
255 return false;
256 }
257 if (Size > SmallDataThreshold) {
258 LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
259 return false;
260 }
261
262 LLVM_DEBUG(dbgs() << "yes\n");
263 return true;
264 }
265
isSmallDataEnabled() const266 bool HexagonTargetObjectFile::isSmallDataEnabled() const {
267 return SmallDataThreshold > 0;
268 }
269
getSmallDataSize() const270 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
271 return SmallDataThreshold;
272 }
273
shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,const Function & F) const274 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
275 bool UsesLabelDifference, const Function &F) const {
276 return EmitJtInText;
277 }
278
279 /// Descends any type down to "elementary" components,
280 /// discovering the smallest addressable one.
281 /// If zero is returned, declaration will not be modified.
getSmallestAddressableSize(const Type * Ty,const GlobalValue * GV,const TargetMachine & TM) const282 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
283 const GlobalValue *GV, const TargetMachine &TM) const {
284 // Assign the smallest element access size to the highest
285 // value which assembler can handle.
286 unsigned SmallestElement = 8;
287
288 if (!Ty)
289 return 0;
290 switch (Ty->getTypeID()) {
291 case Type::StructTyID: {
292 const StructType *STy = cast<const StructType>(Ty);
293 for (auto &E : STy->elements()) {
294 unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
295 if (AtomicSize < SmallestElement)
296 SmallestElement = AtomicSize;
297 }
298 return (STy->getNumElements() == 0) ? 0 : SmallestElement;
299 }
300 case Type::ArrayTyID: {
301 const ArrayType *ATy = cast<const ArrayType>(Ty);
302 return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
303 }
304 case Type::VectorTyID: {
305 const VectorType *PTy = cast<const VectorType>(Ty);
306 return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
307 }
308 case Type::PointerTyID:
309 case Type::HalfTyID:
310 case Type::FloatTyID:
311 case Type::DoubleTyID:
312 case Type::IntegerTyID: {
313 const DataLayout &DL = GV->getParent()->getDataLayout();
314 // It is unfortunate that DL's function take non-const Type*.
315 return DL.getTypeAllocSize(const_cast<Type*>(Ty));
316 }
317 case Type::FunctionTyID:
318 case Type::VoidTyID:
319 case Type::X86_FP80TyID:
320 case Type::FP128TyID:
321 case Type::PPC_FP128TyID:
322 case Type::LabelTyID:
323 case Type::MetadataTyID:
324 case Type::X86_MMXTyID:
325 case Type::TokenTyID:
326 return 0;
327 }
328
329 return 0;
330 }
331
selectSmallSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const332 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
333 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
334 const Type *GTy = GO->getType()->getElementType();
335 unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
336
337 // If we have -ffunction-section or -fdata-section then we should emit the
338 // global value to a unique section specifically for it... even for sdata.
339 bool EmitUniquedSection = TM.getDataSections();
340
341 TRACE("Small data. Size(" << Size << ")");
342 // Handle Small Section classification here.
343 if (Kind.isBSS() || Kind.isBSSLocal()) {
344 // If -mno-sort-sda is not set, find out smallest accessible entity in
345 // declaration and add it to the section name string.
346 // Note. It does not track the actual usage of the value, only its de-
347 // claration. Also, compiler adds explicit pad fields to some struct
348 // declarations - they are currently counted towards smallest addres-
349 // sable entity.
350 if (NoSmallDataSorting) {
351 TRACE(" default sbss\n");
352 return SmallBSSSection;
353 }
354
355 StringRef Prefix(".sbss");
356 SmallString<128> Name(Prefix);
357 Name.append(getSectionSuffixForSize(Size));
358
359 if (EmitUniquedSection) {
360 Name.append(".");
361 Name.append(GO->getName());
362 }
363 TRACE(" unique sbss(" << Name << ")\n");
364 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
365 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
366 }
367
368 if (Kind.isCommon()) {
369 // This is purely for LTO+Linker Script because commons don't really have a
370 // section. However, the BitcodeSectionWriter pass will query for the
371 // sections of commons (and the linker expects us to know their section) so
372 // we'll return one here.
373 if (NoSmallDataSorting)
374 return BSSSection;
375
376 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
377 TRACE(" small COMMON (" << Name << ")\n");
378
379 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
380 ELF::SHF_WRITE | ELF::SHF_ALLOC |
381 ELF::SHF_HEX_GPREL);
382 }
383
384 // We could have changed sdata object to a constant... in this
385 // case the Kind could be wrong for it.
386 if (Kind.isMergeableConst()) {
387 TRACE(" const_object_as_data ");
388 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
389 if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
390 Kind = SectionKind::getData();
391 }
392
393 if (Kind.isData()) {
394 if (NoSmallDataSorting) {
395 TRACE(" default sdata\n");
396 return SmallDataSection;
397 }
398
399 StringRef Prefix(".sdata");
400 SmallString<128> Name(Prefix);
401 Name.append(getSectionSuffixForSize(Size));
402
403 if (EmitUniquedSection) {
404 Name.append(".");
405 Name.append(GO->getName());
406 }
407 TRACE(" unique sdata(" << Name << ")\n");
408 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
409 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
410 }
411
412 TRACE("default ELF section\n");
413 // Otherwise, we work the same as ELF.
414 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
415 }
416
417 // Return the function that uses the lookup table. If there are more
418 // than one live function that uses this look table, bail out and place
419 // the lookup table in default section.
420 const Function *
getLutUsedFunction(const GlobalObject * GO) const421 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
422 const Function *ReturnFn = nullptr;
423 for (auto U : GO->users()) {
424 // validate each instance of user to be a live function.
425 auto *I = dyn_cast<Instruction>(U);
426 if (!I)
427 continue;
428 auto *Bb = I->getParent();
429 if (!Bb)
430 continue;
431 auto *UserFn = Bb->getParent();
432 if (!ReturnFn)
433 ReturnFn = UserFn;
434 else if (ReturnFn != UserFn)
435 return nullptr;
436 }
437 return ReturnFn;
438 }
439
selectSectionForLookupTable(const GlobalObject * GO,const TargetMachine & TM,const Function * Fn) const440 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
441 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
442
443 SectionKind Kind = SectionKind::getText();
444 // If the function has explicit section, place the lookup table in this
445 // explicit section.
446 if (Fn->hasSection())
447 return getExplicitSectionGlobal(Fn, Kind, TM);
448
449 const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
450 return SelectSectionForGlobal(FuncObj, Kind, TM);
451 }
452