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comparison llvm/lib/Target/Hexagon/HexagonTargetObjectFile.cpp @ 150:1d019706d866

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LLVM10
author anatofuz
date Thu, 13 Feb 2020 15:10:13 +0900
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children e8a9b4f4d755 0572611fdcc8
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147:c2174574ed3a 150:1d019706d866
1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
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 contains the declarations of the HexagonTargetAsmInfo properties.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #define DEBUG_TYPE "hexagon-sdata"
14
15 #include "HexagonTargetObjectFile.h"
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/ADT/Twine.h"
19 #include "llvm/BinaryFormat/ELF.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/DerivedTypes.h"
22 #include "llvm/IR/GlobalObject.h"
23 #include "llvm/IR/GlobalValue.h"
24 #include "llvm/IR/GlobalVariable.h"
25 #include "llvm/IR/Type.h"
26 #include "llvm/MC/MCContext.h"
27 #include "llvm/MC/SectionKind.h"
28 #include "llvm/Support/Casting.h"
29 #include "llvm/Support/CommandLine.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include "llvm/Target/TargetMachine.h"
33
34 using namespace llvm;
35
36 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
37 cl::init(8), cl::Hidden,
38 cl::desc("The maximum size of an object in the sdata section"));
39
40 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
41 cl::Hidden, cl::desc("Disable small data sections sorting"));
42
43 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
44 cl::init(false), cl::Hidden, cl::ZeroOrMore,
45 cl::desc("Allow static variables in .sdata"));
46
47 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
48 cl::Hidden, cl::init(false),
49 cl::desc("Trace global value placement"));
50
51 static cl::opt<bool>
52 EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
53 cl::desc("Emit hexagon jump tables in function section"));
54
55 static cl::opt<bool>
56 EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
57 cl::desc("Emit hexagon lookup tables in function section"));
58
59 // TraceGVPlacement controls messages for all builds. For builds with assertions
60 // (debug or release), messages are also controlled by the usual debug flags
61 // (e.g. -debug and -debug-only=globallayout)
62 #define TRACE_TO(s, X) s << X
63 #ifdef NDEBUG
64 #define TRACE(X) \
65 do { \
66 if (TraceGVPlacement) { \
67 TRACE_TO(errs(), X); \
68 } \
69 } while (false)
70 #else
71 #define TRACE(X) \
72 do { \
73 if (TraceGVPlacement) { \
74 TRACE_TO(errs(), X); \
75 } else { \
76 LLVM_DEBUG(TRACE_TO(dbgs(), X)); \
77 } \
78 } while (false)
79 #endif
80
81 // Returns true if the section name is such that the symbol will be put
82 // in a small data section.
83 // For instance, global variables with section attributes such as ".sdata"
84 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
85 static bool isSmallDataSection(StringRef Sec) {
86 // sectionName is either ".sdata" or ".sbss". Looking for an exact match
87 // obviates the need for checks for section names such as ".sdatafoo".
88 if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
89 return true;
90 // If either ".sdata." or ".sbss." is a substring of the section name
91 // then put the symbol in small data.
92 return Sec.find(".sdata.") != StringRef::npos ||
93 Sec.find(".sbss.") != StringRef::npos ||
94 Sec.find(".scommon.") != StringRef::npos;
95 }
96
97 static const char *getSectionSuffixForSize(unsigned Size) {
98 switch (Size) {
99 default:
100 return "";
101 case 1:
102 return ".1";
103 case 2:
104 return ".2";
105 case 4:
106 return ".4";
107 case 8:
108 return ".8";
109 }
110 }
111
112 void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
113 const TargetMachine &TM) {
114 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
115 InitializeELF(TM.Options.UseInitArray);
116
117 SmallDataSection =
118 getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
119 ELF::SHF_WRITE | ELF::SHF_ALLOC |
120 ELF::SHF_HEX_GPREL);
121 SmallBSSSection =
122 getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
123 ELF::SHF_WRITE | ELF::SHF_ALLOC |
124 ELF::SHF_HEX_GPREL);
125 }
126
127 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
128 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
129 TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
130 TRACE("input section(" << GO->getSection() << ") ");
131
132 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
133 << (GO->hasLocalLinkage() ? "local_linkage " : "")
134 << (GO->hasInternalLinkage() ? "internal " : "")
135 << (GO->hasExternalLinkage() ? "external " : "")
136 << (GO->hasCommonLinkage() ? "common_linkage " : "")
137 << (GO->hasCommonLinkage() ? "common " : "" )
138 << (Kind.isCommon() ? "kind_common " : "" )
139 << (Kind.isBSS() ? "kind_bss " : "" )
140 << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
141
142 // If the lookup table is used by more than one function, do not place
143 // it in text section.
144 if (EmitLutInText && GO->getName().startswith("switch.table")) {
145 if (const Function *Fn = getLutUsedFunction(GO))
146 return selectSectionForLookupTable(GO, TM, Fn);
147 }
148
149 if (isGlobalInSmallSection(GO, TM))
150 return selectSmallSectionForGlobal(GO, Kind, TM);
151
152 if (Kind.isCommon()) {
153 // This is purely for LTO+Linker Script because commons don't really have a
154 // section. However, the BitcodeSectionWriter pass will query for the
155 // sections of commons (and the linker expects us to know their section) so
156 // we'll return one here.
157 return BSSSection;
158 }
159
160 TRACE("default_ELF_section\n");
161 // Otherwise, we work the same as ELF.
162 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
163 }
164
165 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
166 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
167 TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
168 << GO->getSection() << ") ");
169 TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
170 << (GO->hasLocalLinkage() ? "local_linkage " : "")
171 << (GO->hasInternalLinkage() ? "internal " : "")
172 << (GO->hasExternalLinkage() ? "external " : "")
173 << (GO->hasCommonLinkage() ? "common_linkage " : "")
174 << (GO->hasCommonLinkage() ? "common " : "" )
175 << (Kind.isCommon() ? "kind_common " : "" )
176 << (Kind.isBSS() ? "kind_bss " : "" )
177 << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
178
179 if (GO->hasSection()) {
180 StringRef Section = GO->getSection();
181 if (Section.find(".access.text.group") != StringRef::npos)
182 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
183 ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
184 if (Section.find(".access.data.group") != StringRef::npos)
185 return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
186 ELF::SHF_WRITE | ELF::SHF_ALLOC);
187 }
188
189 if (isGlobalInSmallSection(GO, TM))
190 return selectSmallSectionForGlobal(GO, Kind, TM);
191
192 // Otherwise, we work the same as ELF.
193 TRACE("default_ELF_section\n");
194 return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
195 }
196
197 /// Return true if this global value should be placed into small data/bss
198 /// section.
199 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
200 const TargetMachine &TM) const {
201 bool HaveSData = isSmallDataEnabled(TM);
202 if (!HaveSData)
203 LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols "
204 "may have explicit section assignments...\n");
205 // Only global variables, not functions.
206 LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
207 << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
208 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
209 if (!GVar) {
210 LLVM_DEBUG(dbgs() << "no, not a global variable\n");
211 return false;
212 }
213
214 // Globals with external linkage that have an original section set must be
215 // emitted to that section, regardless of whether we would put them into
216 // small data or not. This is how we can support mixing -G0/-G8 in LTO.
217 if (GVar->hasSection()) {
218 bool IsSmall = isSmallDataSection(GVar->getSection());
219 LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
220 << ", has section: " << GVar->getSection() << '\n');
221 return IsSmall;
222 }
223
224 // If sdata is disabled, stop the checks here.
225 if (!HaveSData) {
226 LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n");
227 return false;
228 }
229
230 if (GVar->isConstant()) {
231 LLVM_DEBUG(dbgs() << "no, is a constant\n");
232 return false;
233 }
234
235 bool IsLocal = GVar->hasLocalLinkage();
236 if (!StaticsInSData && IsLocal) {
237 LLVM_DEBUG(dbgs() << "no, is static\n");
238 return false;
239 }
240
241 Type *GType = GVar->getValueType();
242 if (isa<ArrayType>(GType)) {
243 LLVM_DEBUG(dbgs() << "no, is an array\n");
244 return false;
245 }
246
247 // If the type is a struct with no body provided, treat is conservatively.
248 // There cannot be actual definitions of object of such a type in this CU
249 // (only references), so assuming that they are not in sdata is safe. If
250 // these objects end up in the sdata, the references will still be valid.
251 if (StructType *ST = dyn_cast<StructType>(GType)) {
252 if (ST->isOpaque()) {
253 LLVM_DEBUG(dbgs() << "no, has opaque type\n");
254 return false;
255 }
256 }
257
258 unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
259 if (Size == 0) {
260 LLVM_DEBUG(dbgs() << "no, has size 0\n");
261 return false;
262 }
263 if (Size > SmallDataThreshold) {
264 LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
265 return false;
266 }
267
268 LLVM_DEBUG(dbgs() << "yes\n");
269 return true;
270 }
271
272 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
273 const {
274 return SmallDataThreshold > 0 && !TM.isPositionIndependent();
275 }
276
277 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
278 return SmallDataThreshold;
279 }
280
281 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
282 bool UsesLabelDifference, const Function &F) const {
283 return EmitJtInText;
284 }
285
286 /// Descends any type down to "elementary" components,
287 /// discovering the smallest addressable one.
288 /// If zero is returned, declaration will not be modified.
289 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
290 const GlobalValue *GV, const TargetMachine &TM) const {
291 // Assign the smallest element access size to the highest
292 // value which assembler can handle.
293 unsigned SmallestElement = 8;
294
295 if (!Ty)
296 return 0;
297 switch (Ty->getTypeID()) {
298 case Type::StructTyID: {
299 const StructType *STy = cast<const StructType>(Ty);
300 for (auto &E : STy->elements()) {
301 unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
302 if (AtomicSize < SmallestElement)
303 SmallestElement = AtomicSize;
304 }
305 return (STy->getNumElements() == 0) ? 0 : SmallestElement;
306 }
307 case Type::ArrayTyID: {
308 const ArrayType *ATy = cast<const ArrayType>(Ty);
309 return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
310 }
311 case Type::VectorTyID: {
312 const VectorType *PTy = cast<const VectorType>(Ty);
313 return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
314 }
315 case Type::PointerTyID:
316 case Type::HalfTyID:
317 case Type::FloatTyID:
318 case Type::DoubleTyID:
319 case Type::IntegerTyID: {
320 const DataLayout &DL = GV->getParent()->getDataLayout();
321 // It is unfortunate that DL's function take non-const Type*.
322 return DL.getTypeAllocSize(const_cast<Type*>(Ty));
323 }
324 case Type::FunctionTyID:
325 case Type::VoidTyID:
326 case Type::X86_FP80TyID:
327 case Type::FP128TyID:
328 case Type::PPC_FP128TyID:
329 case Type::LabelTyID:
330 case Type::MetadataTyID:
331 case Type::X86_MMXTyID:
332 case Type::TokenTyID:
333 return 0;
334 }
335
336 return 0;
337 }
338
339 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
340 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
341 const Type *GTy = GO->getValueType();
342 unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
343
344 // If we have -ffunction-section or -fdata-section then we should emit the
345 // global value to a unique section specifically for it... even for sdata.
346 bool EmitUniquedSection = TM.getDataSections();
347
348 TRACE("Small data. Size(" << Size << ")");
349 // Handle Small Section classification here.
350 if (Kind.isBSS() || Kind.isBSSLocal()) {
351 // If -mno-sort-sda is not set, find out smallest accessible entity in
352 // declaration and add it to the section name string.
353 // Note. It does not track the actual usage of the value, only its de-
354 // claration. Also, compiler adds explicit pad fields to some struct
355 // declarations - they are currently counted towards smallest addres-
356 // sable entity.
357 if (NoSmallDataSorting) {
358 TRACE(" default sbss\n");
359 return SmallBSSSection;
360 }
361
362 StringRef Prefix(".sbss");
363 SmallString<128> Name(Prefix);
364 Name.append(getSectionSuffixForSize(Size));
365
366 if (EmitUniquedSection) {
367 Name.append(".");
368 Name.append(GO->getName());
369 }
370 TRACE(" unique sbss(" << Name << ")\n");
371 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
372 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
373 }
374
375 if (Kind.isCommon()) {
376 // This is purely for LTO+Linker Script because commons don't really have a
377 // section. However, the BitcodeSectionWriter pass will query for the
378 // sections of commons (and the linker expects us to know their section) so
379 // we'll return one here.
380 if (NoSmallDataSorting)
381 return BSSSection;
382
383 Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
384 TRACE(" small COMMON (" << Name << ")\n");
385
386 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
387 ELF::SHF_WRITE | ELF::SHF_ALLOC |
388 ELF::SHF_HEX_GPREL);
389 }
390
391 // We could have changed sdata object to a constant... in this
392 // case the Kind could be wrong for it.
393 if (Kind.isMergeableConst()) {
394 TRACE(" const_object_as_data ");
395 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
396 if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
397 Kind = SectionKind::getData();
398 }
399
400 if (Kind.isData()) {
401 if (NoSmallDataSorting) {
402 TRACE(" default sdata\n");
403 return SmallDataSection;
404 }
405
406 StringRef Prefix(".sdata");
407 SmallString<128> Name(Prefix);
408 Name.append(getSectionSuffixForSize(Size));
409
410 if (EmitUniquedSection) {
411 Name.append(".");
412 Name.append(GO->getName());
413 }
414 TRACE(" unique sdata(" << Name << ")\n");
415 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
416 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
417 }
418
419 TRACE("default ELF section\n");
420 // Otherwise, we work the same as ELF.
421 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
422 }
423
424 // Return the function that uses the lookup table. If there are more
425 // than one live function that uses this look table, bail out and place
426 // the lookup table in default section.
427 const Function *
428 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
429 const Function *ReturnFn = nullptr;
430 for (auto U : GO->users()) {
431 // validate each instance of user to be a live function.
432 auto *I = dyn_cast<Instruction>(U);
433 if (!I)
434 continue;
435 auto *Bb = I->getParent();
436 if (!Bb)
437 continue;
438 auto *UserFn = Bb->getParent();
439 if (!ReturnFn)
440 ReturnFn = UserFn;
441 else if (ReturnFn != UserFn)
442 return nullptr;
443 }
444 return ReturnFn;
445 }
446
447 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
448 const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
449
450 SectionKind Kind = SectionKind::getText();
451 // If the function has explicit section, place the lookup table in this
452 // explicit section.
453 if (Fn->hasSection())
454 return getExplicitSectionGlobal(Fn, Kind, TM);
455
456 const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
457 return SelectSectionForGlobal(FuncObj, Kind, TM);
458 }