[MC] Remove nullable getCurrentSectionOnly use from AsmParser

We will implement getCurrentSectionOnly with `CurFrag->getParent()`,
which is non-null. Eliminate a nullable use.

Author: MaskRay

llvm/include/llvm/MC/MCObjectStreamer.h

@@ -26,8 +26,6 @@ class MCAssembler;
 class MCCodeEmitter;
 class MCSubtargetInfo;
 class MCExpr;
-class MCFragment;
-class MCDataFragment;
 class MCAsmBackend;
 class raw_ostream;
 class raw_pwrite_stream;
@@ -85,8 +83,6 @@ class MCObjectStreamer : public MCStreamer {
   void emitFrames(MCAsmBackend *MAB);
   void emitCFISections(bool EH, bool Debug) override;
 
-  MCFragment *getCurrentFragment() const;
-
   void insert(MCFragment *F) {
     auto *Sec = CurFrag->getParent();
     F->setParent(Sec);

llvm/include/llvm/MC/MCStreamer.h

@@ -255,15 +255,15 @@ class MCStreamer {
   /// discussion for future inclusion.
   bool AllowAutoPadding = false;
 
-  /// This is called by popSection and switchSection, if the current
-  /// section changes.
-  virtual void changeSection(MCSection *, uint32_t);
-
 protected:
   MCFragment *CurFrag = nullptr;
 
   MCStreamer(MCContext &Ctx);
 
+  /// This is called by popSection and switchSection, if the current
+  /// section changes.
+  virtual void changeSection(MCSection *, uint32_t);
+
   virtual void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame);
   virtual void emitCFIEndProcImpl(MCDwarfFrameInfo &CurFrame);
 
@@ -408,6 +408,8 @@ class MCStreamer {
     return MCSectionSubPair();
   }
 
+  MCFragment *getCurrentFragment() const;
+
   /// Returns an index to represent the order a symbol was emitted in.
   /// (zero if we did not emit that symbol)
   unsigned getSymbolOrder(const MCSymbol *Sym) const {

llvm/lib/MC/MCAsmStreamer.cpp

@@ -511,8 +511,7 @@ void MCAsmStreamer::emitExplicitComments() {
 }
 
 void MCAsmStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
-  assert(Section && "Cannot switch to a null section!");
-  CurFrag = &Section->getDummyFragment();
+  MCStreamer::changeSection(Section, Subsection);
   if (MCTargetStreamer *TS = getTargetStreamer()) {
     TS->changeSection(getCurrentSectionOnly(), Section, Subsection, OS);
   } else {

llvm/lib/MC/MCELFStreamer.cpp

@@ -107,13 +107,14 @@ static void setSectionAlignmentForBundling(const MCAssembler &Assembler,
 }
 
 void MCELFStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
-  MCSection *CurSection = getCurrentSectionOnly();
-  if (CurSection && isBundleLocked())
-    report_fatal_error("Unterminated .bundle_lock when changing a section");
-
   MCAssembler &Asm = getAssembler();
-  // Ensure the previous section gets aligned if necessary.
-  setSectionAlignmentForBundling(Asm, CurSection);
+  if (auto *F = getCurrentFragment()) {
+    if (isBundleLocked())
+      report_fatal_error("Unterminated .bundle_lock when changing a section");
+
+    // Ensure the previous section gets aligned if necessary.
+    setSectionAlignmentForBundling(Asm, F->getParent());
+  }
   auto *SectionELF = static_cast<const MCSectionELF *>(Section);
   const MCSymbol *Grp = SectionELF->getGroup();
   if (Grp)

llvm/lib/MC/MCObjectStreamer.cpp

@@ -142,12 +142,6 @@ void MCObjectStreamer::emitFrames(MCAsmBackend *MAB) {
     MCDwarfFrameEmitter::Emit(*this, MAB, false);
 }
 
-MCFragment *MCObjectStreamer::getCurrentFragment() const {
-  assert(!getCurrentSection().first ||
-         CurFrag->getParent() == getCurrentSection().first);
-  return CurFrag;
-}
-
 static bool canReuseDataFragment(const MCDataFragment &F,
                                  const MCAssembler &Assembler,
                                  const MCSubtargetInfo *STI) {

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -1082,7 +1082,7 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
 }
 
 bool AsmParser::checkForValidSection() {
-  if (!ParsingMSInlineAsm && !getStreamer().getCurrentSectionOnly()) {
+  if (!ParsingMSInlineAsm && !getStreamer().getCurrentFragment()) {
     Out.initSections(false, getTargetParser().getSTI());
     return Error(getTok().getLoc(),
                  "expected section directive before assembly directive");

llvm/lib/MC/MCStreamer.cpp

@@ -118,6 +118,12 @@ ArrayRef<MCDwarfFrameInfo> MCStreamer::getDwarfFrameInfos() const {
   return DwarfFrameInfos;
 }
 
+MCFragment *MCStreamer::getCurrentFragment() const {
+  assert(!getCurrentSection().first ||
+         CurFrag->getParent() == getCurrentSection().first);
+  return CurFrag;
+}
+
 void MCStreamer::emitRawComment(const Twine &T, bool TabPrefix) {}
 
 void MCStreamer::addExplicitComment(const Twine &T) {}
@@ -1218,7 +1224,9 @@ void MCStreamer::emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                        Align ByteAlignment) {}
 void MCStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                 uint64_t Size, Align ByteAlignment) {}
-void MCStreamer::changeSection(MCSection *, uint32_t) {}
+void MCStreamer::changeSection(MCSection *Section, uint32_t) {
+  CurFrag = &Section->getDummyFragment();
+}
 void MCStreamer::emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {}
 void MCStreamer::emitBytes(StringRef Data) {}
 void MCStreamer::emitBinaryData(StringRef Data) { emitBytes(Data); }