There is only one current section.

Both MCStreamer and MCObjectStreamer were maintaining a current section
variable and they were slightly out of sync. I don't think this was observable,
but was inefficient and error prone.

Changing this requires a few cascading changes:

* SwitchSection has to call ChangeSection earlier for ChangeSection to see
  the old section.
* With that change, ChangeSection cannot call EmitLabel, since during
  ChangeSection we are still in the old section.
* When the object streamer requires a begin label, just reused the existing
  generic support for begin labels instead of calling EmitLabel directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238357 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCObjectStreamer.h

@@ -35,7 +35,6 @@ class raw_pwrite_stream;
 /// implementation.
 class MCObjectStreamer : public MCStreamer {
   MCAssembler *Assembler;
-  MCSection *CurSectionData;
   MCSection::iterator CurInsertionPoint;
   bool EmitEHFrame;
   bool EmitDebugFrame;
@@ -64,14 +63,15 @@ public:
   void EmitCFISections(bool EH, bool Debug) override;
 
 protected:
-  MCSection *getCurrentSectionData() const { return CurSectionData; }
+  MCSection *getCurrentSectionData() const { return getCurrentSection().first; }
 
   MCFragment *getCurrentFragment() const;
 
   void insert(MCFragment *F) {
     flushPendingLabels(F);
-    CurSectionData->getFragmentList().insert(CurInsertionPoint, F);
-    F->setParent(CurSectionData);
+    MCSection *CurSection = getCurrentSectionData();
+    CurSection->getFragmentList().insert(CurInsertionPoint, F);
+    F->setParent(CurSection);
   }
 
   /// Get a data fragment to write into, creating a new one if the current

lib/MC/ELFObjectWriter.cpp

@@ -821,9 +821,7 @@ void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
     const MCSection *SecA =
         (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
     auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
-    MCSymbol *SectionSymbol =
-        ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
-               : nullptr;
+    const MCSymbol *SectionSymbol = ELFSec ? ELFSec->getBeginSymbol() : nullptr;
     ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
     Relocations[&FixupSection].push_back(Rec);
     return;
@@ -882,6 +880,9 @@ bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
   if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
     return false;
 
+  if (MCELF::GetType(Data) == ELF::STT_SECTION)
+    return true;
+
   if (Symbol.isTemporary())
     return false;
 

lib/MC/MCELFStreamer.cpp

@@ -159,11 +159,14 @@ void MCELFStreamer::ChangeSection(MCSection *Section,
     Asm.getOrCreateSymbolData(*Grp);
 
   this->MCObjectStreamer::ChangeSection(Section, Subsection);
-  MCSymbol *SectionSymbol = getContext().getOrCreateSectionSymbol(*SectionELF);
-  if (SectionSymbol->isUndefined()) {
-    EmitLabel(SectionSymbol);
-    MCELF::SetType(Asm.getSymbolData(*SectionSymbol), ELF::STT_SECTION);
+  MCContext &Ctx = getContext();
+  MCSymbol *Begin = Section->getBeginSymbol();
+  if (!Begin) {
+    Begin = Ctx.getOrCreateSectionSymbol(*SectionELF);
+    Section->setBeginSymbol(Begin);
   }
+  if (Begin->isUndefined())
+    MCELF::SetType(Asm.getOrCreateSymbolData(*Begin), ELF::STT_SECTION);
 }
 
 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {

lib/MC/MCMachOStreamer.cpp

@@ -162,9 +162,10 @@ void MCMachOStreamer::ChangeSection(MCSection *Section,
 
   // Output a linker-local symbol so we don't need section-relative local
   // relocations. The linker hates us when we do that.
-  if (LabelSections && !HasSectionLabel[Section]) {
+  if (LabelSections && !HasSectionLabel[Section] &&
+      !Section->getBeginSymbol()) {
     MCSymbol *Label = getContext().createLinkerPrivateTempSymbol();
-    EmitLabel(Label);
+    Section->setBeginSymbol(Label);
     HasSectionLabel[Section] = true;
   }
 }

lib/MC/MCObjectStreamer.cpp

@@ -29,7 +29,7 @@ MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
     : MCStreamer(Context),
       Assembler(new MCAssembler(Context, TAB, *Emitter_,
                                 *TAB.createObjectWriter(OS), OS)),
-      CurSectionData(nullptr), EmitEHFrame(true), EmitDebugFrame(false) {}
+      EmitEHFrame(true), EmitDebugFrame(false) {}
 
 MCObjectStreamer::~MCObjectStreamer() {
   delete &Assembler->getBackend();
@@ -42,8 +42,9 @@ void MCObjectStreamer::flushPendingLabels(MCFragment *F, uint64_t FOffset) {
   if (PendingLabels.size()) {
     if (!F) {
       F = new MCDataFragment();
-      CurSectionData->getFragmentList().insert(CurInsertionPoint, F);
-      F->setParent(CurSectionData);
+      MCSection *CurSection = getCurrentSectionData();
+      CurSection->getFragmentList().insert(CurInsertionPoint, F);
+      F->setParent(CurSection);
     }
     for (MCSymbolData *SD : PendingLabels) {
       SD->setFragment(F);
@@ -79,7 +80,6 @@ bool MCObjectStreamer::emitAbsoluteSymbolDiff(const MCSymbol *Hi,
 void MCObjectStreamer::reset() {
   if (Assembler)
     Assembler->reset();
-  CurSectionData = nullptr;
   CurInsertionPoint = MCSection::iterator();
   EmitEHFrame = true;
   EmitDebugFrame = false;
@@ -212,7 +212,6 @@ bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
   flushPendingLabels(nullptr);
 
   bool Created = getAssembler().registerSection(*Section);
-  CurSectionData = Section;
 
   int64_t IntSubsection = 0;
   if (Subsection &&
@@ -221,7 +220,7 @@ bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
   if (IntSubsection < 0 || IntSubsection > 8192)
     report_fatal_error("Subsection number out of range");
   CurInsertionPoint =
-      CurSectionData->getSubsectionInsertionPoint(unsigned(IntSubsection));
+      Section->getSubsectionInsertionPoint(unsigned(IntSubsection));
   return Created;
 }
 

lib/MC/MCParser/AsmParser.cpp

@@ -630,13 +630,15 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
   // If we are generating dwarf for assembly source files save the initial text
   // section and generate a .file directive.
   if (getContext().getGenDwarfForAssembly()) {
-    MCSymbol *SectionStartSym = getContext().createTempSymbol();
-    getStreamer().EmitLabel(SectionStartSym);
     MCSection *Sec = getStreamer().getCurrentSection().first;
+    if (!Sec->getBeginSymbol()) {
+      MCSymbol *SectionStartSym = getContext().createTempSymbol();
+      getStreamer().EmitLabel(SectionStartSym);
+      Sec->setBeginSymbol(SectionStartSym);
+    }
     bool InsertResult = getContext().addGenDwarfSection(Sec);
     assert(InsertResult && ".text section should not have debug info yet");
     (void)InsertResult;
-    Sec->setBeginSymbol(SectionStartSym);
     getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
         0, StringRef(), getContext().getMainFileName()));
   }

lib/MC/MCParser/ELFAsmParser.cpp

@@ -537,9 +537,11 @@ EndStmt:
       if (getContext().getDwarfVersion() <= 2)
         Warning(loc, "DWARF2 only supports one section per compilation unit");
 
-      MCSymbol *SectionStartSymbol = getContext().createTempSymbol();
-      getStreamer().EmitLabel(SectionStartSymbol);
-      ELFSection->setBeginSymbol(SectionStartSymbol);
+      if (!ELFSection->getBeginSymbol()) {
+        MCSymbol *SectionStartSymbol = getContext().createTempSymbol();
+        getStreamer().EmitLabel(SectionStartSymbol);
+        ELFSection->setBeginSymbol(SectionStartSymbol);
+      }
     }
   }
 

lib/MC/MCStreamer.cpp

@@ -669,9 +669,9 @@ void MCStreamer::SwitchSection(MCSection *Section, const MCExpr *Subsection) {
   MCSectionSubPair curSection = SectionStack.back().first;
   SectionStack.back().second = curSection;
   if (MCSectionSubPair(Section, Subsection) != curSection) {
+    ChangeSection(Section, Subsection);
     SectionStack.back().first = MCSectionSubPair(Section, Subsection);
     assert(!Section->hasEnded() && "Section already ended");
-    ChangeSection(Section, Subsection);
     MCSymbol *Sym = Section->getBeginSymbol();
     if (Sym && !Sym->isInSection())
       EmitLabel(Sym);