lib/Target/Mips/MipsTargetObjectFile.cpp

   1 //===-- MipsTargetObjectFile.cpp - Mips object files ----------------------===//
   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 #include "MipsTargetObjectFile.h"
  11 #include "MipsSubtarget.h"
  12 #include "llvm/DerivedTypes.h"
  13 #include "llvm/GlobalVariable.h"
  14 #include "llvm/MC/MCContext.h"
  15 #include "llvm/MC/MCSectionELF.h"
  16 #include "llvm/Target/TargetData.h"
  17 #include "llvm/Target/TargetMachine.h"
  18 #include "llvm/Support/CommandLine.h"
  19 using namespace llvm;
  20
  21 static cl::opt<unsigned>
  22 SSThreshold("mips-ssection-threshold", cl::Hidden,
  23             cl::desc("Small data and bss section threshold size (default=8)"),
  24             cl::init(8));
  25
  26 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
  27   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
  28
  29   SmallDataSection =
  30     getContext().getELFSection(".sdata", MCSectionELF::SHT_PROGBITS,
  31                                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
  32                                SectionKind::getDataRel());
  33
  34   SmallBSSSection =
  35     getContext().getELFSection(".sbss", MCSectionELF::SHT_NOBITS,
  36                                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
  37                                SectionKind::getBSS());
  38
  39 }
  40
  41 // A address must be loaded from a small section if its size is less than the
  42 // small section size threshold. Data in this section must be addressed using
  43 // gp_rel operator.
  44 static bool IsInSmallSection(uint64_t Size) {
  45   return Size > 0 && Size <= SSThreshold;
  46 }
  47
  48 bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
  49                                                 const TargetMachine &TM) const {
  50   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
  51     return false;
  52
  53   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
  54 }
  55
  56 /// IsGlobalInSmallSection - Return true if this global address should be
  57 /// placed into small data/bss section.
  58 bool MipsTargetObjectFile::
  59 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
  60                        SectionKind Kind) const {
  61
  62   // Only use small section for non linux targets.
  63   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
  64   if (Subtarget.isLinux())
  65     return false;
  66
  67   // Only global variables, not functions.
  68   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
  69   if (!GVA)
  70     return false;
  71
  72   // We can only do this for datarel or BSS objects for now.
  73   if (!Kind.isBSS() && !Kind.isDataRel())
  74     return false;
  75
  76   // If this is a internal constant string, there is a special
  77   // section for it, but not in small data/bss.
  78   if (Kind.isMergeable1ByteCString())
  79     return false;
  80
  81   const Type *Ty = GV->getType()->getElementType();
  82   return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
  83 }
  84
  85
  86
  87 const MCSection *MipsTargetObjectFile::
  88 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
  89                        Mangler *Mang, const TargetMachine &TM) const {
  90   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
  91   // sections?
  92
  93   // Handle Small Section classification here.
  94   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
  95     return SmallBSSSection;
  96   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
  97     return SmallDataSection;
  98
  99   // Otherwise, we work the same as ELF.
 100   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
 101 }