Revert "Remove doesSectionRequireSymbols."

This reverts commit r224985.

I am investigating why it made an Apple bot unhappy.

llvm-svn: 225044
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 83a76dc..e4442e1 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -219,7 +219,7 @@
                                   const MCSymbolData *SD, uint64_t C,
                                   unsigned Type) const;
 
-    void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+    void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
                           const MCFragment *Fragment, const MCFixup &Fixup,
                           MCValue Target, bool &IsPCRel,
                           uint64_t &FixedValue) override;
@@ -789,11 +789,13 @@
   return nullptr;
 }
 
-void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
+void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
                                        const MCAsmLayout &Layout,
                                        const MCFragment *Fragment,
-                                       const MCFixup &Fixup, MCValue Target,
-                                       bool &IsPCRel, uint64_t &FixedValue) {
+                                       const MCFixup &Fixup,
+                                       MCValue Target,
+                                       bool &IsPCRel,
+                                       uint64_t &FixedValue) {
   const MCSectionData *FixupSection = Fragment->getParent();
   uint64_t C = Target.getConstant();
   uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
diff --git a/llvm/lib/MC/MCAsmInfoDarwin.cpp b/llvm/lib/MC/MCAsmInfoDarwin.cpp
index a616c5b..f346b93 100644
--- a/llvm/lib/MC/MCAsmInfoDarwin.cpp
+++ b/llvm/lib/MC/MCAsmInfoDarwin.cpp
@@ -27,7 +27,22 @@
   // contain.
   // Sections holding 2 byte strings require symbols in order to be atomized.
   // There is no dedicated section for 4 byte strings.
-  if (SMO.getType() == MachO::S_CSTRING_LITERALS)
+  if (SMO.getKind().isMergeable1ByteCString())
+    return false;
+
+  if (SMO.getSegmentName() == "__TEXT" &&
+      SMO.getSectionName() == "__objc_classname" &&
+      SMO.getType() == MachO::S_CSTRING_LITERALS)
+    return false;
+
+  if (SMO.getSegmentName() == "__TEXT" &&
+      SMO.getSectionName() == "__objc_methname" &&
+      SMO.getType() == MachO::S_CSTRING_LITERALS)
+    return false;
+
+  if (SMO.getSegmentName() == "__TEXT" &&
+      SMO.getSectionName() == "__objc_methtype" &&
+      SMO.getType() == MachO::S_CSTRING_LITERALS)
     return false;
 
   if (SMO.getSegmentName() == "__DATA" && SMO.getSectionName() == "__cfstring")
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index a4af21e..459488b 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -425,16 +425,6 @@
   return true;
 }
 
-void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
-  assert(Sym.isTemporary());
-  LocalsUsedInReloc.insert(&Sym);
-}
-
-bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
-  assert(Sym.isTemporary());
-  return LocalsUsedInReloc.count(&Sym);
-}
-
 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
   // Non-temporary labels should always be visible to the linker.
   if (!Symbol.isTemporary())
@@ -444,10 +434,8 @@
   if (!Symbol.isInSection())
     return false;
 
-  if (isLocalUsedInReloc(Symbol))
-    return true;
-
-  return false;
+  // Otherwise, check if the section requires symbols even for temporary labels.
+  return getBackend().doesSectionRequireSymbols(Symbol.getSection());
 }
 
 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index 588d424..d3751bd 100644
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -448,11 +448,14 @@
   assert(OS.tell() - Start == Size);
 }
 
-void MachObjectWriter::RecordRelocation(MCAssembler &Asm,
+
+void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
                                         const MCAsmLayout &Layout,
                                         const MCFragment *Fragment,
-                                        const MCFixup &Fixup, MCValue Target,
-                                        bool &IsPCRel, uint64_t &FixedValue) {
+                                        const MCFixup &Fixup,
+                                        MCValue Target,
+                                        bool &IsPCRel,
+                                        uint64_t &FixedValue) {
   TargetObjectWriter->RecordRelocation(this, Asm, Layout, Fragment, Fixup,
                                        Target, FixedValue);
 }
@@ -613,22 +616,6 @@
     ExternalSymbolData[i].SymbolData->setIndex(Index++);
   for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
     UndefinedSymbolData[i].SymbolData->setIndex(Index++);
-
-  for (const MCSectionData &SD : Asm) {
-    std::vector<RelAndSymbol> &Relocs = Relocations[&SD];
-    for (RelAndSymbol &Rel : Relocs) {
-      if (!Rel.Sym)
-        continue;
-
-      // Set the Index and the IsExtern bit.
-      unsigned Index = Rel.Sym->getIndex();
-      assert(isInt<24>(Index));
-      if (IsLittleEndian)
-        Rel.MRE.r_word1 = (Rel.MRE.r_word1 & (-1 << 24)) | Index | (1 << 27);
-      else
-        Rel.MRE.r_word1 = (Rel.MRE.r_word1 & 0xff) | Index << 8 | (1 << 4);
-    }
-  }
 }
 
 void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
@@ -675,6 +662,10 @@
   // Mark symbol difference expressions in variables (from .set or = directives)
   // as absolute.
   markAbsoluteVariableSymbols(Asm, Layout);
+
+  // Compute symbol table information and bind symbol indices.
+  ComputeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
+                     UndefinedSymbolData);
 }
 
 bool MachObjectWriter::
@@ -758,10 +749,6 @@
 
 void MachObjectWriter::WriteObject(MCAssembler &Asm,
                                    const MCAsmLayout &Layout) {
-  // Compute symbol table information and bind symbol indices.
-  ComputeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
-                     UndefinedSymbolData);
-
   unsigned NumSections = Asm.size();
   const MCAssembler::VersionMinInfoType &VersionInfo =
     Layout.getAssembler().getVersionMinInfo();
@@ -852,7 +839,7 @@
   uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
   for (MCAssembler::const_iterator it = Asm.begin(),
          ie = Asm.end(); it != ie; ++it) {
-    std::vector<RelAndSymbol> &Relocs = Relocations[it];
+    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
     unsigned NumRelocs = Relocs.size();
     uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
     WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
@@ -946,10 +933,10 @@
          ie = Asm.end(); it != ie; ++it) {
     // Write the section relocation entries, in reverse order to match 'as'
     // (approximately, the exact algorithm is more complicated than this).
-    std::vector<RelAndSymbol> &Relocs = Relocations[it];
+    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
     for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
-      Write32(Relocs[e - i - 1].MRE.r_word0);
-      Write32(Relocs[e - i - 1].MRE.r_word1);
+      Write32(Relocs[e - i - 1].r_word0);
+      Write32(Relocs[e - i - 1].r_word1);
     }
   }
 
diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index 2cb247a..2180b42 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -175,7 +175,7 @@
                                               const MCFragment &FB, bool InSet,
                                               bool IsPCRel) const override;
 
-  void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+  void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, bool &IsPCRel,
                         uint64_t &FixedValue) override;
@@ -661,9 +661,13 @@
                                                                 InSet, IsPCRel);
 }
 
-void WinCOFFObjectWriter::RecordRelocation(
-    MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
-    const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
+void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,
+                                           const MCAsmLayout &Layout,
+                                           const MCFragment *Fragment,
+                                           const MCFixup &Fixup,
+                                           MCValue Target,
+                                           bool &IsPCRel,
+                                           uint64_t &FixedValue) {
   assert(Target.getSymA() && "Relocation must reference a symbol!");
 
   const MCSymbol &Symbol = Target.getSymA()->getSymbol();
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
index 0df442f..0bc2f77 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
@@ -317,6 +317,42 @@
                                          MachO::CPU_SUBTYPE_ARM64_ALL);
   }
 
+  bool doesSectionRequireSymbols(const MCSection &Section) const override {
+    // Any section for which the linker breaks things into atoms needs to
+    // preserve symbols, including assembler local symbols, to identify
+    // those atoms. These sections are:
+    // Sections of type:
+    //
+    //    S_CSTRING_LITERALS  (e.g. __cstring)
+    //    S_LITERAL_POINTERS  (e.g.  objc selector pointers)
+    //    S_16BYTE_LITERALS, S_8BYTE_LITERALS, S_4BYTE_LITERALS
+    //
+    // Sections named:
+    //
+    //    __TEXT,__eh_frame
+    //    __TEXT,__ustring
+    //    __DATA,__cfstring
+    //    __DATA,__objc_classrefs
+    //    __DATA,__objc_catlist
+    //
+    // FIXME: It would be better if the compiler used actual linker local
+    // symbols for each of these sections rather than preserving what
+    // are ostensibly assembler local symbols.
+    const MCSectionMachO &SMO = static_cast<const MCSectionMachO &>(Section);
+    return (SMO.getType() == MachO::S_CSTRING_LITERALS ||
+            SMO.getType() == MachO::S_4BYTE_LITERALS ||
+            SMO.getType() == MachO::S_8BYTE_LITERALS ||
+            SMO.getType() == MachO::S_16BYTE_LITERALS ||
+            SMO.getType() == MachO::S_LITERAL_POINTERS ||
+            (SMO.getSegmentName() == "__TEXT" &&
+             (SMO.getSectionName() == "__eh_frame" ||
+              SMO.getSectionName() == "__ustring")) ||
+            (SMO.getSegmentName() == "__DATA" &&
+             (SMO.getSectionName() == "__cfstring" ||
+              SMO.getSectionName() == "__objc_classrefs" ||
+              SMO.getSectionName() == "__objc_catlist")));
+  }
+
   /// \brief Generate the compact unwind encoding from the CFI directives.
   uint32_t generateCompactUnwindEncoding(
                              ArrayRef<MCCFIInstruction> Instrs) const override {
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
index 2ea3826..e12a24b 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
@@ -10,7 +10,6 @@
 #include "MCTargetDesc/AArch64FixupKinds.h"
 #include "MCTargetDesc/AArch64MCTargetDesc.h"
 #include "llvm/ADT/Twine.h"
-#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCAsmLayout.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCContext.h"
@@ -34,7 +33,7 @@
       : MCMachObjectTargetWriter(true /* is64Bit */, CPUType, CPUSubtype,
                                  /*UseAggressiveSymbolFolding=*/true) {}
 
-  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
+  void RecordRelocation(MachObjectWriter *Writer, const MCAssembler &Asm,
                         const MCAsmLayout &Layout, const MCFragment *Fragment,
                         const MCFixup &Fixup, MCValue Target,
                         uint64_t &FixedValue) override;
@@ -114,7 +113,7 @@
 }
 
 void AArch64MachObjectWriter::RecordRelocation(
-    MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout,
+    MachObjectWriter *Writer, const MCAssembler &Asm, const MCAsmLayout &Layout,
     const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
     uint64_t &FixedValue) {
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
@@ -124,9 +123,9 @@
   unsigned Log2Size = 0;
   int64_t Value = 0;
   unsigned Index = 0;
+  unsigned IsExtern = 0;
   unsigned Type = 0;
   unsigned Kind = Fixup.getKind();
-  const MCSymbolData *RelSymbol = nullptr;
 
   FixupOffset += Fixup.getOffset();
 
@@ -172,8 +171,10 @@
     // FIXME: Should this always be extern?
     // SymbolNum of 0 indicates the absolute section.
     Type = MachO::ARM64_RELOC_UNSIGNED;
+    Index = 0;
 
     if (IsPCRel) {
+      IsExtern = 1;
       Asm.getContext().FatalError(Fixup.getLoc(),
                                   "PC relative absolute relocation!");
 
@@ -197,12 +198,15 @@
         Layout.getSymbolOffset(&B_SD) ==
             Layout.getFragmentOffset(Fragment) + Fixup.getOffset()) {
       // SymB is the PC, so use a PC-rel pointer-to-GOT relocation.
+      Index = A_Base->getIndex();
+      IsExtern = 1;
       Type = MachO::ARM64_RELOC_POINTER_TO_GOT;
       IsPCRel = 1;
       MachO::any_relocation_info MRE;
       MRE.r_word0 = FixupOffset;
-      MRE.r_word1 = (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-      Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
+      MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
+                     (IsExtern << 27) | (Type << 28));
+      Writer->addRelocation(Fragment->getParent(), MRE);
       return;
     } else if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
                Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
@@ -248,23 +252,21 @@
                   ? 0
                   : Writer->getSymbolAddress(B_Base, Layout));
 
+    Index = A_Base->getIndex();
+    IsExtern = 1;
     Type = MachO::ARM64_RELOC_UNSIGNED;
 
     MachO::any_relocation_info MRE;
     MRE.r_word0 = FixupOffset;
-    MRE.r_word1 = (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-    Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
+    MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
+                   (IsExtern << 27) | (Type << 28));
+    Writer->addRelocation(Fragment->getParent(), MRE);
 
-    RelSymbol = B_Base;
+    Index = B_Base->getIndex();
+    IsExtern = 1;
     Type = MachO::ARM64_RELOC_SUBTRACTOR;
   } else { // A + constant
     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
-    if (Symbol->isTemporary() && Value) {
-      const MCSection &Sec = Symbol->getSection();
-      if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec))
-        Asm.addLocalUsedInReloc(*Symbol);
-    }
-
     const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
     const MCSymbolData *Base = Asm.getAtom(&SD);
     const MCSectionMachO &Section = static_cast<const MCSectionMachO &>(
@@ -308,7 +310,8 @@
     // sections, and for pointer-sized relocations (.quad), we allow section
     // relocations.  It's code sections that run into trouble.
     if (Base) {
-      RelSymbol = Base;
+      Index = Base->getIndex();
+      IsExtern = 1;
 
       // Add the local offset, if needed.
       if (Base != &SD)
@@ -326,6 +329,7 @@
       const MCSectionData &SymSD =
           Asm.getSectionData(SD.getSymbol().getSection());
       Index = SymSD.getOrdinal() + 1;
+      IsExtern = 0;
       Value += Writer->getSymbolAddress(&SD, Layout);
 
       if (IsPCRel)
@@ -358,16 +362,16 @@
 
     MachO::any_relocation_info MRE;
     MRE.r_word0 = FixupOffset;
-    MRE.r_word1 =
-        (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-    Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+    MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
+                   (IsExtern << 27) | (Type << 28));
+    Writer->addRelocation(Fragment->getParent(), MRE);
 
     // Now set up the Addend relocation.
     Type = MachO::ARM64_RELOC_ADDEND;
     Index = Value;
-    RelSymbol = nullptr;
     IsPCRel = 0;
     Log2Size = 2;
+    IsExtern = 0;
 
     // Put zero into the instruction itself. The addend is in the relocation.
     Value = 0;
@@ -379,9 +383,9 @@
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 =
-      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+  MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
+                 (IsExtern << 27) | (Type << 28));
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_ostream &OS,
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 3187d36..7da5003 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -54,10 +54,10 @@
     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                /*UseAggressiveSymbolFolding=*/true) {}
 
-  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
-                        const MCAsmLayout &Layout, const MCFragment *Fragment,
-                        const MCFixup &Fixup, MCValue Target,
-                        uint64_t &FixedValue) override;
+  void RecordRelocation(MachObjectWriter *Writer,
+                        const MCAssembler &Asm, const MCAsmLayout &Layout,
+                        const MCFragment *Fragment, const MCFixup &Fixup,
+                        MCValue Target, uint64_t &FixedValue) override;
 };
 }
 
@@ -232,7 +232,7 @@
                    (IsPCRel               << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = Value2;
-    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+    Writer->addRelocation(Fragment->getParent(), MRE);
   }
 
   MachO::any_relocation_info MRE;
@@ -243,7 +243,7 @@
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
@@ -297,7 +297,7 @@
                    (IsPCRel               << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = Value2;
-    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+    Writer->addRelocation(Fragment->getParent(), MRE);
   }
 
   MachO::any_relocation_info MRE;
@@ -307,7 +307,7 @@
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
@@ -351,10 +351,11 @@
 }
 
 void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
-                                           MCAssembler &Asm,
+                                           const MCAssembler &Asm,
                                            const MCAsmLayout &Layout,
                                            const MCFragment *Fragment,
-                                           const MCFixup &Fixup, MCValue Target,
+                                           const MCFixup &Fixup,
+                                           MCValue Target,
                                            uint64_t &FixedValue) {
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
   unsigned Log2Size;
@@ -400,8 +401,8 @@
   // See <reloc.h>.
   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
   unsigned Index = 0;
+  unsigned IsExtern = 0;
   unsigned Type = 0;
-  const MCSymbolData *RelSymbol = nullptr;
 
   if (Target.isAbsolute()) { // constant
     // FIXME!
@@ -421,7 +422,8 @@
     // Check whether we need an external or internal relocation.
     if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
                                  FixedValue)) {
-      RelSymbol = SD;
+      IsExtern = 1;
+      Index = SD->getIndex();
 
       // For external relocations, make sure to offset the fixup value to
       // compensate for the addend of the symbol address, if it was
@@ -445,8 +447,11 @@
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 =
-      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
+  MRE.r_word1 = ((Index     <<  0) |
+                 (IsPCRel   << 24) |
+                 (Log2Size  << 25) |
+                 (IsExtern  << 27) |
+                 (Type      << 28));
 
   // Even when it's not a scattered relocation, movw/movt always uses
   // a PAIR relocation.
@@ -471,10 +476,10 @@
                        (Log2Size              << 25) |
                        (MachO::ARM_RELOC_PAIR << 28));
 
-    Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
+    Writer->addRelocation(Fragment->getParent(), MREPair);
   }
 
-  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createARMMachObjectWriter(raw_ostream &OS,
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
index f7259b9..df2f14a 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
@@ -41,7 +41,7 @@
       : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                  /*UseAggressiveSymbolFolding=*/Is64Bit) {}
 
-  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
+  void RecordRelocation(MachObjectWriter *Writer, const MCAssembler &Asm,
                         const MCAsmLayout &Layout, const MCFragment *Fragment,
                         const MCFixup &Fixup, MCValue Target,
                         uint64_t &FixedValue) override {
@@ -282,7 +282,7 @@
     MachO::any_relocation_info MRE;
     makeScatteredRelocationInfo(MRE, other_half, MachO::GENERIC_RELOC_PAIR,
                                 Log2Size, IsPCRel, Value2);
-    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+    Writer->addRelocation(Fragment->getParent(), MRE);
   } else {
     // If the offset is more than 24-bits, it won't fit in a scattered
     // relocation offset field, so we fall back to using a non-scattered
@@ -296,7 +296,7 @@
   }
   MachO::any_relocation_info MRE;
   makeScatteredRelocationInfo(MRE, FixupOffset, Type, Log2Size, IsPCRel, Value);
-  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+  Writer->addRelocation(Fragment->getParent(), MRE);
   return true;
 }
 
@@ -331,9 +331,9 @@
   // See <reloc.h>.
   const uint32_t FixupOffset = getFixupOffset(Layout, Fragment, Fixup);
   unsigned Index = 0;
+  unsigned IsExtern = 0;
   unsigned Type = RelocType;
 
-  const MCSymbolData *RelSymbol = nullptr;
   if (Target.isAbsolute()) { // constant
                              // SymbolNum of 0 indicates the absolute section.
                              //
@@ -355,7 +355,8 @@
 
     // Check whether we need an external or internal relocation.
     if (Writer->doesSymbolRequireExternRelocation(SD)) {
-      RelSymbol = SD;
+      IsExtern = 1;
+      Index = SD->getIndex();
       // For external relocations, make sure to offset the fixup value to
       // compensate for the addend of the symbol address, if it was
       // undefined. This occurs with weak definitions, for example.
@@ -374,8 +375,9 @@
 
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
-  makeRelocationInfo(MRE, FixupOffset, Index, IsPCRel, Log2Size, false, Type);
-  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+  makeRelocationInfo(MRE, FixupOffset, Index, IsPCRel, Log2Size, IsExtern,
+                     Type);
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createPPCMachObjectWriter(raw_ostream &OS, bool Is64Bit,
diff --git a/llvm/lib/Target/R600/MCTargetDesc/AMDGPUAsmBackend.cpp b/llvm/lib/Target/R600/MCTargetDesc/AMDGPUAsmBackend.cpp
index d0c634f..5fb311b 100644
--- a/llvm/lib/Target/R600/MCTargetDesc/AMDGPUAsmBackend.cpp
+++ b/llvm/lib/Target/R600/MCTargetDesc/AMDGPUAsmBackend.cpp
@@ -29,7 +29,7 @@
                                 const MCAsmLayout &Layout) override {
     //XXX: Implement if necessary.
   }
-  void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+  void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, bool &IsPCRel,
                         uint64_t &FixedValue) override {
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 719b761..164b419 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -777,6 +777,19 @@
                                      MachO::CPU_TYPE_X86_64, Subtype);
   }
 
+  bool doesSectionRequireSymbols(const MCSection &Section) const override {
+    // Temporary labels in the string literals sections require symbols. The
+    // issue is that the x86_64 relocation format does not allow symbol +
+    // offset, and so the linker does not have enough information to resolve the
+    // access to the appropriate atom unless an external relocation is used. For
+    // non-cstring sections, we expect the compiler to use a non-temporary label
+    // for anything that could have an addend pointing outside the symbol.
+    //
+    // See <rdar://problem/4765733>.
+    const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
+    return SMO.getType() == MachO::S_CSTRING_LITERALS;
+  }
+
   /// \brief Generate the compact unwind encoding for the CFI instructions.
   uint32_t generateCompactUnwindEncoding(
                              ArrayRef<MCCFIInstruction> Instrs) const override {
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
index 7a83f4c..67b0c89 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
@@ -10,7 +10,6 @@
 #include "MCTargetDesc/X86MCTargetDesc.h"
 #include "MCTargetDesc/X86FixupKinds.h"
 #include "llvm/ADT/Twine.h"
-#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCAsmLayout.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCContext.h"
@@ -48,21 +47,23 @@
                               const MCFixup &Fixup,
                               MCValue Target,
                               uint64_t &FixedValue);
-  void RecordX86_64Relocation(MachObjectWriter *Writer, MCAssembler &Asm,
+  void RecordX86_64Relocation(MachObjectWriter *Writer,
+                              const MCAssembler &Asm,
                               const MCAsmLayout &Layout,
-                              const MCFragment *Fragment, const MCFixup &Fixup,
-                              MCValue Target, uint64_t &FixedValue);
-
+                              const MCFragment *Fragment,
+                              const MCFixup &Fixup,
+                              MCValue Target,
+                              uint64_t &FixedValue);
 public:
   X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
                       uint32_t CPUSubtype)
     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                /*UseAggressiveSymbolFolding=*/Is64Bit) {}
 
-  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
-                        const MCAsmLayout &Layout, const MCFragment *Fragment,
-                        const MCFixup &Fixup, MCValue Target,
-                        uint64_t &FixedValue) override {
+  void RecordRelocation(MachObjectWriter *Writer,
+                        const MCAssembler &Asm, const MCAsmLayout &Layout,
+                        const MCFragment *Fragment, const MCFixup &Fixup,
+                        MCValue Target, uint64_t &FixedValue) override {
     if (Writer->is64Bit())
       RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
                              FixedValue);
@@ -96,10 +97,13 @@
   }
 }
 
-void X86MachObjectWriter::RecordX86_64Relocation(
-    MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout,
-    const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
-    uint64_t &FixedValue) {
+void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
+                                                 const MCAssembler &Asm,
+                                                 const MCAsmLayout &Layout,
+                                                 const MCFragment *Fragment,
+                                                 const MCFixup &Fixup,
+                                                 MCValue Target,
+                                                 uint64_t &FixedValue) {
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
   unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
@@ -113,7 +117,6 @@
   unsigned Index = 0;
   unsigned IsExtern = 0;
   unsigned Type = 0;
-  const MCSymbolData *RelSymbol = nullptr;
 
   Value = Target.getConstant();
 
@@ -129,6 +132,7 @@
   if (Target.isAbsolute()) { // constant
     // SymbolNum of 0 indicates the absolute section.
     Type = MachO::X86_64_RELOC_UNSIGNED;
+    Index = 0;
 
     // FIXME: I believe this is broken, I don't think the linker can understand
     // it. I think it would require a local relocation, but I'm not sure if that
@@ -189,30 +193,36 @@
     Value -= Writer->getSymbolAddress(&B_SD, Layout) -
       (!B_Base ? 0 : Writer->getSymbolAddress(B_Base, Layout));
 
-    if (!A_Base)
+    if (A_Base) {
+      Index = A_Base->getIndex();
+      IsExtern = 1;
+    } else {
       Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
+      IsExtern = 0;
+    }
     Type = MachO::X86_64_RELOC_UNSIGNED;
 
     MachO::any_relocation_info MRE;
     MRE.r_word0 = FixupOffset;
-    MRE.r_word1 =
-        (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-    Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
+    MRE.r_word1 = ((Index     <<  0) |
+                   (IsPCRel   << 24) |
+                   (Log2Size  << 25) |
+                   (IsExtern  << 27) |
+                   (Type      << 28));
+    Writer->addRelocation(Fragment->getParent(), MRE);
 
-    if (B_Base)
-      RelSymbol = B_Base;
-    else
+    if (B_Base) {
+      Index = B_Base->getIndex();
+      IsExtern = 1;
+    } else {
       Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
+      IsExtern = 0;
+    }
     Type = MachO::X86_64_RELOC_SUBTRACTOR;
   } else {
     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
-    if (Symbol->isTemporary() && Value) {
-      const MCSection &Sec = Symbol->getSection();
-      if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec))
-        Asm.addLocalUsedInReloc(*Symbol);
-    }
     const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
-    RelSymbol = Asm.getAtom(&SD);
+    const MCSymbolData *Base = Asm.getAtom(&SD);
 
     // Relocations inside debug sections always use local relocations when
     // possible. This seems to be done because the debugger doesn't fully
@@ -222,20 +232,23 @@
       const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
         Fragment->getParent()->getSection());
       if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
-        RelSymbol = nullptr;
+        Base = nullptr;
     }
 
     // x86_64 almost always uses external relocations, except when there is no
     // symbol to use as a base address (a local symbol with no preceding
     // non-local symbol).
-    if (RelSymbol) {
+    if (Base) {
+      Index = Base->getIndex();
+      IsExtern = 1;
+
       // Add the local offset, if needed.
-      if (RelSymbol != &SD)
-        Value +=
-            Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(RelSymbol);
+      if (Base != &SD)
+        Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
     } else if (Symbol->isInSection() && !Symbol->isVariable()) {
       // The index is the section ordinal (1-based).
       Index = SD.getFragment()->getParent()->getOrdinal() + 1;
+      IsExtern = 0;
       Value += Writer->getSymbolAddress(&SD, Layout);
 
       if (IsPCRel)
@@ -334,9 +347,12 @@
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
-                (IsExtern << 27) | (Type << 28);
-  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+  MRE.r_word1 = ((Index     <<  0) |
+                 (IsPCRel   << 24) |
+                 (Log2Size  << 25) |
+                 (IsExtern  << 27) |
+                 (Type      << 28));
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
@@ -408,7 +424,7 @@
                    (IsPCRel                   << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = Value2;
-    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+    Writer->addRelocation(Fragment->getParent(), MRE);
   } else {
     // If the offset is more than 24-bits, it won't fit in a scattered
     // relocation offset field, so we fall back to using a non-scattered
@@ -430,7 +446,7 @@
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
+  Writer->addRelocation(Fragment->getParent(), MRE);
   return true;
 }
 
@@ -451,6 +467,7 @@
 
   // Get the symbol data.
   const MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
+  unsigned Index = SD_A->getIndex();
 
   // We're only going to have a second symbol in pic mode and it'll be a
   // subtraction from the picbase. For 32-bit pic the addend is the difference
@@ -473,9 +490,12 @@
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = Value;
-  MRE.r_word1 =
-      (IsPCRel << 24) | (Log2Size << 25) | (MachO::GENERIC_RELOC_TLV << 28);
-  Writer->addRelocation(SD_A, Fragment->getParent(), MRE);
+  MRE.r_word1 = ((Index                    <<  0) |
+                 (IsPCRel                  << 24) |
+                 (Log2Size                 << 25) |
+                 (1                        << 27) | // r_extern
+                 (MachO::GENERIC_RELOC_TLV << 28)); // r_type
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
@@ -526,8 +546,8 @@
   // See <reloc.h>.
   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
   unsigned Index = 0;
+  unsigned IsExtern = 0;
   unsigned Type = 0;
-  const MCSymbolData *RelSymbol = nullptr;
 
   if (Target.isAbsolute()) { // constant
     // SymbolNum of 0 indicates the absolute section.
@@ -548,7 +568,8 @@
 
     // Check whether we need an external or internal relocation.
     if (Writer->doesSymbolRequireExternRelocation(SD)) {
-      RelSymbol = SD;
+      IsExtern = 1;
+      Index = SD->getIndex();
       // For external relocations, make sure to offset the fixup value to
       // compensate for the addend of the symbol address, if it was
       // undefined. This occurs with weak definitions, for example.
@@ -570,9 +591,12 @@
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 =
-      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
-  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
+  MRE.r_word1 = ((Index     <<  0) |
+                 (IsPCRel   << 24) |
+                 (Log2Size  << 25) |
+                 (IsExtern  << 27) |
+                 (Type      << 28));
+  Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,