MCFragment: Migrate away from appendContents

The fixed-size content of the MCFragment object will be stored as
trailing data (#150846). Any post-assembler-layout adjustments must
target the variable-size tail.

Author: MaskRay

llvm/include/llvm/MC/MCObjectStreamer.h

@@ -87,6 +87,7 @@ class MCObjectStreamer : public MCStreamer {
   // Add a new fragment to the current section without a variable-size tail.
   void newFragment();
 
+  void appendContents(ArrayRef<char> Contents);
   void appendContents(size_t Num, char Elt);
   void addFixup(const MCExpr *Value, MCFixupKind Kind);
 

llvm/lib/MC/MCMachOStreamer.cpp

@@ -484,7 +484,8 @@ void MCMachOStreamer::finalizeCGProfile() {
   // For each entry, reserve space for 2 32-bit indices and a 64-bit count.
   size_t SectionBytes =
       W.getCGProfile().size() * (2 * sizeof(uint32_t) + sizeof(uint64_t));
-  (*CGProfileSection->begin()).appendContents(SectionBytes, 0);
+  (*CGProfileSection->begin())
+      .setVarContents(std::vector<char>(SectionBytes, 0));
 }
 
 MCStreamer *llvm::createMachOStreamer(MCContext &Context,
@@ -520,5 +521,6 @@ void MCMachOStreamer::createAddrSigSection() {
   // (instead of emitting a zero-sized section) so these relocations are
   // technically valid, even though we don't expect these relocations to
   // actually be applied by the linker.
-  Frag->appendContents(8, 0);
+  constexpr char zero[8] = {};
+  Frag->setVarContents(zero);
 }

llvm/lib/MC/MCObjectStreamer.cpp

@@ -57,6 +57,10 @@ void MCObjectStreamer::insert(MCFragment *F) {
   newFragment();
 }
 
+void MCObjectStreamer::appendContents(ArrayRef<char> Contents) {
+  CurFrag->appendContents(Contents);
+}
+
 void MCObjectStreamer::appendContents(size_t Num, char Elt) {
   CurFrag->appendContents(Num, Elt);
 }
@@ -538,8 +542,7 @@ void MCObjectStreamer::emitCVFileChecksumOffsetDirective(unsigned FileNo) {
 
 void MCObjectStreamer::emitBytes(StringRef Data) {
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
-  MCFragment *DF = getCurrentFragment();
-  DF->appendContents(ArrayRef(Data.data(), Data.size()));
+  appendContents(ArrayRef(Data.data(), Data.size()));
 }
 
 void MCObjectStreamer::emitValueToAlignment(Align Alignment, int64_t Fill,

llvm/lib/MC/MachObjectWriter.cpp

@@ -806,7 +806,7 @@ uint64_t MachObjectWriter::writeObject() {
     }
     MCSection *Sec = getContext().getMachOSection("__LLVM", "__cg_profile", 0,
                                                   SectionKind::getMetadata());
-    llvm::copy(OS.str(), Sec->curFragList()->Head->getContents().data());
+    llvm::copy(OS.str(), Sec->curFragList()->Head->getVarContents().data());
   }
 
   unsigned NumSections = Asm.end() - Asm.begin();