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