HexagonTargetObjectFile.cpp revision 344779 
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
35using namespace llvm;
36
37static 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
41static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
42  cl::Hidden, cl::desc("Disable small data sections sorting"));
43
44static 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
48static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
49  cl::Hidden, cl::init(false),
50  cl::desc("Trace global value placement"));
51
52static 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
56static 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.
86static 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
98static 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
113void 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
128MCSection *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
166MCSection *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.
200bool 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
276bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
277    const {
278  return SmallDataThreshold > 0 && !TM.isPositionIndependent();
279}
280
281unsigned HexagonTargetObjectFile::getSmallDataSize() const {
282  return SmallDataThreshold;
283}
284
285bool 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.
293unsigned 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
343MCSection *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.
431const Function *
432HexagonTargetObjectFile::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
451MCSection *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