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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