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