HexagonTargetObjectFile.cpp revision 341825 
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  // 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
266bool HexagonTargetObjectFile::isSmallDataEnabled() const {
267  return SmallDataThreshold > 0;
268}
269
270unsigned HexagonTargetObjectFile::getSmallDataSize() const {
271  return SmallDataThreshold;
272}
273
274bool 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.
282unsigned 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
332MCSection *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.
420const Function *
421HexagonTargetObjectFile::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
440MCSection *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