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 bool HaveSData = isSmallDataEnabled(TM);
203 if (!HaveSData)
204 LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols "
205 "may have explicit section assignments...\n");
206 // Only global variables, not functions.
207 LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
208 << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
209 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
210 if (!GVar) {
211 LLVM_DEBUG(dbgs() << "no, not a global variable\n");
212 return false;
213 }
214
215 // Globals with external linkage that have an original section set must be
216 // emitted to that section, regardless of whether we would put them into
217 // small data or not. This is how we can support mixing -G0/-G8 in LTO.
218 if (GVar->hasSection()) {
219 bool IsSmall = isSmallDataSection(GVar->getSection());
220 LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
221 << ", has section: " << GVar->getSection() << '\n');
222 return IsSmall;
223 }
224
225 // If sdata is disabled, stop the checks here.
226 if (!HaveSData) {
227 LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n");
228 return false;
229 }
230
231 if (GVar->isConstant()) {
232 LLVM_DEBUG(dbgs() << "no, is a constant\n");
233 return false;
234 }
235
236 bool IsLocal = GVar->hasLocalLinkage();
237 if (!StaticsInSData && IsLocal) {
238 LLVM_DEBUG(dbgs() << "no, is static\n");
239 return false;
240 }
241
242 Type *GType = GVar->getType();
243 if (PointerType *PT = dyn_cast<PointerType>(GType))
244 GType = PT->getElementType();
245
246 if (isa<ArrayType>(GType)) {
247 LLVM_DEBUG(dbgs() << "no, is an array\n");
248 return false;
249 }
250
251 // If the type is a struct with no body provided, treat is conservatively.
252 // There cannot be actual definitions of object of such a type in this CU
253 // (only references), so assuming that they are not in sdata is safe. If
254 // these objects end up in the sdata, the references will still be valid.
255 if (StructType *ST = dyn_cast<StructType>(GType)) {
256 if (ST->isOpaque()) {
257 LLVM_DEBUG(dbgs() << "no, has opaque type\n");
258 return false;
259 }
260 }
261
262 unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
263 if (Size == 0) {
264 LLVM_DEBUG(dbgs() << "no, has size 0\n");
265 return false;
266 }
267 if (Size > SmallDataThreshold) {
268 LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
269 return false;
270 }
271
272 LLVM_DEBUG(dbgs() << "yes\n");
273 return true;
274 }
275
isSmallDataEnabled(const TargetMachine & TM) const276 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
277 const {
278 return SmallDataThreshold > 0 && !TM.isPositionIndependent();
279 }
280
getSmallDataSize() const281 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
282 return SmallDataThreshold;
283 }
284
shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,const Function & F) const285 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
286 bool UsesLabelDifference, const Function &F) const {
287 return EmitJtInText;
288 }
289
290 /// Descends any type down to "elementary" components,
291 /// discovering the smallest addressable one.
292 /// If zero is returned, declaration will not be modified.
getSmallestAddressableSize(const Type * Ty,const GlobalValue * GV,const TargetMachine & TM) const293 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
294 const GlobalValue *GV, const TargetMachine &TM) const {
295 // Assign the smallest element access size to the highest
296 // value which assembler can handle.
297 unsigned SmallestElement = 8;
298
299 if (!Ty)
300 return 0;
301 switch (Ty->getTypeID()) {
302 case Type::StructTyID: {
303 const StructType *STy = cast<const StructType>(Ty);
304 for (auto &E : STy->elements()) {
305 unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
306 if (AtomicSize < SmallestElement)
307 SmallestElement = AtomicSize;
308 }
309 return (STy->getNumElements() == 0) ? 0 : SmallestElement;
310 }
311 case Type::ArrayTyID: {
312 const ArrayType *ATy = cast<const ArrayType>(Ty);
313 return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
314 }
315 case Type::VectorTyID: {
316 const VectorType *PTy = cast<const VectorType>(Ty);
317 return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
318 }
319 case Type::PointerTyID:
320 case Type::HalfTyID:
321 case Type::FloatTyID:
322 case Type::DoubleTyID:
323 case Type::IntegerTyID: {
324 const DataLayout &DL = GV->getParent()->getDataLayout();
325 // It is unfortunate that DL's function take non-const Type*.
326 return DL.getTypeAllocSize(const_cast<Type*>(Ty));
327 }
328 case Type::FunctionTyID:
329 case Type::VoidTyID:
330 case Type::X86_FP80TyID:
331 case Type::FP128TyID:
332 case Type::PPC_FP128TyID:
333 case Type::LabelTyID:
334 case Type::MetadataTyID:
335 case Type::X86_MMXTyID:
336 case Type::TokenTyID:
337 return 0;
338 }
339
340 return 0;
341 }
342
selectSmallSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const343 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
344 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
345 const Type *GTy = GO->getType()->getElementType();
346 unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
347
348 // If we have -ffunction-section or -fdata-section then we should emit the
349 // global value to a unique section specifically for it... even for sdata.
350 bool EmitUniquedSection = TM.getDataSections();
351
352 TRACE("Small data. Size(" << Size << ")");
353 // Handle Small Section classification here.
354 if (Kind.isBSS() || Kind.isBSSLocal()) {
355 // If -mno-sort-sda is not set, find out smallest accessible entity in
356 // declaration and add it to the section name string.
357 // Note. It does not track the actual usage of the value, only its de-
358 // claration. Also, compiler adds explicit pad fields to some struct
359 // declarations - they are currently counted towards smallest addres-
360 // sable entity.
361 if (NoSmallDataSorting) {
362 TRACE(" default sbss\n");
363 return SmallBSSSection;
364 }
365
366 StringRef Prefix(".sbss");
367 SmallString<128> Name(Prefix);
368 Name.append(getSectionSuffixForSize(Size));
369
370 if (EmitUniquedSection) {
371 Name.append(".");
372 Name.append(GO->getName());
373 }
374 TRACE(" unique sbss(" << Name << ")\n");
375 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
376 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
377 }
378
379 if (Kind.isCommon()) {
380 // This is purely for LTO+Linker Script because commons don't really have a
381 // section. However, the BitcodeSectionWriter pass will query for the
382 // sections of commons (and the linker expects us to know their section) so
383 // we'll return one here.
384 if (NoSmallDataSorting)
385 return BSSSection;
386
387 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
388 TRACE(" small COMMON (" << Name << ")\n");
389
390 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
391 ELF::SHF_WRITE | ELF::SHF_ALLOC |
392 ELF::SHF_HEX_GPREL);
393 }
394
395 // We could have changed sdata object to a constant... in this
396 // case the Kind could be wrong for it.
397 if (Kind.isMergeableConst()) {
398 TRACE(" const_object_as_data ");
399 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
400 if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
401 Kind = SectionKind::getData();
402 }
403
404 if (Kind.isData()) {
405 if (NoSmallDataSorting) {
406 TRACE(" default sdata\n");
407 return SmallDataSection;
408 }
409
410 StringRef Prefix(".sdata");
411 SmallString<128> Name(Prefix);
412 Name.append(getSectionSuffixForSize(Size));
413
414 if (EmitUniquedSection) {
415 Name.append(".");
416 Name.append(GO->getName());
417 }
418 TRACE(" unique sdata(" << Name << ")\n");
419 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
420 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
421 }
422
423 TRACE("default ELF section\n");
424 // Otherwise, we work the same as ELF.
425 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
426 }
427
428 // Return the function that uses the lookup table. If there are more
429 // than one live function that uses this look table, bail out and place
430 // the lookup table in default section.
431 const Function *
getLutUsedFunction(const GlobalObject * GO) const432 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
433 const Function *ReturnFn = nullptr;
434 for (auto U : GO->users()) {
435 // validate each instance of user to be a live function.
436 auto *I = dyn_cast<Instruction>(U);
437 if (!I)
438 continue;
439 auto *Bb = I->getParent();
440 if (!Bb)
441 continue;
442 auto *UserFn = Bb->getParent();
443 if (!ReturnFn)
444 ReturnFn = UserFn;
445 else if (ReturnFn != UserFn)
446 return nullptr;
447 }
448 return ReturnFn;
449 }
450
selectSectionForLookupTable(const GlobalObject * GO,const TargetMachine & TM,const Function * Fn) const451 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
452 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
453
454 SectionKind Kind = SectionKind::getText();
455 // If the function has explicit section, place the lookup table in this
456 // explicit section.
457 if (Fn->hasSection())
458 return getExplicitSectionGlobal(Fn, Kind, TM);
459
460 const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
461 return SelectSectionForGlobal(FuncObj, Kind, TM);
462 }
463