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.
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 
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 
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 
128 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 
166 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.
200 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
201       const TargetMachine &TM) const {
202   if (!isSmallDataEnabled(TM)) {
203     LLVM_DEBUG(dbgs() << "Small data is not available.\n");
204     return false;
205   }
206 
207   // Only global variables, not functions.
208   LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
209                     << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
210   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
211   if (!GVar) {
212     LLVM_DEBUG(dbgs() << "no, not a global variable\n");
213     return false;
214   }
215 
216   // Globals with external linkage that have an original section set must be
217   // emitted to that section, regardless of whether we would put them into
218   // small data or not. This is how we can support mixing -G0/-G8 in LTO.
219   if (GVar->hasSection()) {
220     bool IsSmall = isSmallDataSection(GVar->getSection());
221     LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
222                       << ", has section: " << GVar->getSection() << '\n');
223     return IsSmall;
224   }
225 
226   if (GVar->isConstant()) {
227     LLVM_DEBUG(dbgs() << "no, is a constant\n");
228     return false;
229   }
230 
231   bool IsLocal = GVar->hasLocalLinkage();
232   if (!StaticsInSData && IsLocal) {
233     LLVM_DEBUG(dbgs() << "no, is static\n");
234     return false;
235   }
236 
237   Type *GType = GVar->getType();
238   if (PointerType *PT = dyn_cast<PointerType>(GType))
239     GType = PT->getElementType();
240 
241   if (isa<ArrayType>(GType)) {
242     LLVM_DEBUG(dbgs() << "no, is an array\n");
243     return false;
244   }
245 
246   // If the type is a struct with no body provided, treat is conservatively.
247   // There cannot be actual definitions of object of such a type in this CU
248   // (only references), so assuming that they are not in sdata is safe. If
249   // these objects end up in the sdata, the references will still be valid.
250   if (StructType *ST = dyn_cast<StructType>(GType)) {
251     if (ST->isOpaque()) {
252       LLVM_DEBUG(dbgs() << "no, has opaque type\n");
253       return false;
254     }
255   }
256 
257   unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
258   if (Size == 0) {
259     LLVM_DEBUG(dbgs() << "no, has size 0\n");
260     return false;
261   }
262   if (Size > SmallDataThreshold) {
263     LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
264     return false;
265   }
266 
267   LLVM_DEBUG(dbgs() << "yes\n");
268   return true;
269 }
270 
271 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
272     const {
273   return SmallDataThreshold > 0 && !TM.isPositionIndependent();
274 }
275 
276 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
277   return SmallDataThreshold;
278 }
279 
280 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
281     bool UsesLabelDifference, const Function &F) const {
282   return EmitJtInText;
283 }
284 
285 /// Descends any type down to "elementary" components,
286 /// discovering the smallest addressable one.
287 /// If zero is returned, declaration will not be modified.
288 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
289       const GlobalValue *GV, const TargetMachine &TM) const {
290   // Assign the smallest element access size to the highest
291   // value which assembler can handle.
292   unsigned SmallestElement = 8;
293 
294   if (!Ty)
295     return 0;
296   switch (Ty->getTypeID()) {
297   case Type::StructTyID: {
298     const StructType *STy = cast<const StructType>(Ty);
299     for (auto &E : STy->elements()) {
300       unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
301       if (AtomicSize < SmallestElement)
302         SmallestElement = AtomicSize;
303     }
304     return (STy->getNumElements() == 0) ? 0 : SmallestElement;
305   }
306   case Type::ArrayTyID: {
307     const ArrayType *ATy = cast<const ArrayType>(Ty);
308     return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
309   }
310   case Type::VectorTyID: {
311     const VectorType *PTy = cast<const VectorType>(Ty);
312     return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
313   }
314   case Type::PointerTyID:
315   case Type::HalfTyID:
316   case Type::FloatTyID:
317   case Type::DoubleTyID:
318   case Type::IntegerTyID: {
319     const DataLayout &DL = GV->getParent()->getDataLayout();
320     // It is unfortunate that DL's function take non-const Type*.
321     return DL.getTypeAllocSize(const_cast<Type*>(Ty));
322   }
323   case Type::FunctionTyID:
324   case Type::VoidTyID:
325   case Type::X86_FP80TyID:
326   case Type::FP128TyID:
327   case Type::PPC_FP128TyID:
328   case Type::LabelTyID:
329   case Type::MetadataTyID:
330   case Type::X86_MMXTyID:
331   case Type::TokenTyID:
332     return 0;
333   }
334 
335   return 0;
336 }
337 
338 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
339     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
340   const Type *GTy = GO->getType()->getElementType();
341   unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
342 
343   // If we have -ffunction-section or -fdata-section then we should emit the
344   // global value to a unique section specifically for it... even for sdata.
345   bool EmitUniquedSection = TM.getDataSections();
346 
347   TRACE("Small data. Size(" << Size << ")");
348   // Handle Small Section classification here.
349   if (Kind.isBSS() || Kind.isBSSLocal()) {
350     // If -mno-sort-sda is not set, find out smallest accessible entity in
351     // declaration and add it to the section name string.
352     // Note. It does not track the actual usage of the value, only its de-
353     // claration. Also, compiler adds explicit pad fields to some struct
354     // declarations - they are currently counted towards smallest addres-
355     // sable entity.
356     if (NoSmallDataSorting) {
357       TRACE(" default sbss\n");
358       return SmallBSSSection;
359     }
360 
361     StringRef Prefix(".sbss");
362     SmallString<128> Name(Prefix);
363     Name.append(getSectionSuffixForSize(Size));
364 
365     if (EmitUniquedSection) {
366       Name.append(".");
367       Name.append(GO->getName());
368     }
369     TRACE(" unique sbss(" << Name << ")\n");
370     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
371                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
372   }
373 
374   if (Kind.isCommon()) {
375     // This is purely for LTO+Linker Script because commons don't really have a
376     // section. However, the BitcodeSectionWriter pass will query for the
377     // sections of commons (and the linker expects us to know their section) so
378     // we'll return one here.
379     if (NoSmallDataSorting)
380       return BSSSection;
381 
382     Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
383     TRACE(" small COMMON (" << Name << ")\n");
384 
385     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
386                                       ELF::SHF_WRITE | ELF::SHF_ALLOC |
387                                       ELF::SHF_HEX_GPREL);
388   }
389 
390   // We could have changed sdata object to a constant... in this
391   // case the Kind could be wrong for it.
392   if (Kind.isMergeableConst()) {
393     TRACE(" const_object_as_data ");
394     const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
395     if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
396       Kind = SectionKind::getData();
397   }
398 
399   if (Kind.isData()) {
400     if (NoSmallDataSorting) {
401       TRACE(" default sdata\n");
402       return SmallDataSection;
403     }
404 
405     StringRef Prefix(".sdata");
406     SmallString<128> Name(Prefix);
407     Name.append(getSectionSuffixForSize(Size));
408 
409     if (EmitUniquedSection) {
410       Name.append(".");
411       Name.append(GO->getName());
412     }
413     TRACE(" unique sdata(" << Name << ")\n");
414     return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
415                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
416   }
417 
418   TRACE("default ELF section\n");
419   // Otherwise, we work the same as ELF.
420   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
421 }
422 
423 // Return the function that uses the lookup table. If there are more
424 // than one live function that uses this look table, bail out and place
425 // the lookup table in default section.
426 const Function *
427 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
428   const Function *ReturnFn = nullptr;
429   for (auto U : GO->users()) {
430     // validate each instance of user to be a live function.
431     auto *I = dyn_cast<Instruction>(U);
432     if (!I)
433       continue;
434     auto *Bb = I->getParent();
435     if (!Bb)
436       continue;
437     auto *UserFn = Bb->getParent();
438     if (!ReturnFn)
439       ReturnFn = UserFn;
440     else if (ReturnFn != UserFn)
441       return nullptr;
442   }
443   return ReturnFn;
444 }
445 
446 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
447     const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
448 
449   SectionKind Kind = SectionKind::getText();
450   // If the function has explicit section, place the lookup table in this
451   // explicit section.
452   if (Fn->hasSection())
453     return getExplicitSectionGlobal(Fn, Kind, TM);
454 
455   const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
456   return SelectSectionForGlobal(FuncObj, Kind, TM);
457 }
458