[MC] Move MCAsmLayout::SectionOrder to MachObjectWriter::SectionOrder

Follow-up to 2c1fb41.

SectionOrder is Mach-O specific to place zerofill sections after
non-zerofill sections in the object writer.

Author: MaskRay

llvm/include/llvm/MC/MCAsmLayout.h

@@ -16,33 +16,14 @@ namespace llvm {
 class MCAssembler;
 class MCSection;
 
-/// Encapsulates the layout of an assembly file at a particular point in time.
-///
-/// Assembly may require computing multiple layouts for a particular assembly
-/// file as part of the relaxation process. This class encapsulates the layout
-/// at a single point in time in such a way that it is always possible to
-/// efficiently compute the exact address of any symbol in the assembly file,
-/// even during the relaxation process.
 class MCAsmLayout {
   MCAssembler &Assembler;
 
-  /// List of sections in layout order.
-  llvm::SmallVector<MCSection *, 16> SectionOrder;
-
 public:
   MCAsmLayout(MCAssembler &Assembler);
 
   /// Get the assembler object this is a layout for.
   MCAssembler &getAssembler() const { return Assembler; }
-
-
-  /// \name Section Access (in layout order)
-  /// @{
-
-  llvm::SmallVectorImpl<MCSection *> &getSectionOrder() { return SectionOrder; }
-  const llvm::SmallVectorImpl<MCSection *> &getSectionOrder() const {
-    return SectionOrder;
-  }
 };
 
 } // end namespace llvm

llvm/include/llvm/MC/MCMachObjectWriter.h

@@ -109,6 +109,10 @@ class MachObjectWriter : public MCObjectWriter {
 
   SectionAddrMap SectionAddress;
 
+  // List of sections in layout order. Virtual sections are after non-virtual
+  // sections.
+  SmallVector<MCSection *, 0> SectionOrder;
+
   /// @}
   /// \name Symbol Table Data
   /// @{
@@ -149,6 +153,9 @@ class MachObjectWriter : public MCObjectWriter {
 
   bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
 
+  const llvm::SmallVectorImpl<MCSection *> &getSectionOrder() const {
+    return SectionOrder;
+  }
   SectionAddrMap &getSectionAddressMap() { return SectionAddress; }
 
   uint64_t getSectionAddress(const MCSection *Sec) const {

llvm/lib/MC/MCAssembler.cpp

@@ -381,15 +381,7 @@ uint64_t MCAssembler::computeFragmentSize(const MCFragment &F) const {
   llvm_unreachable("invalid fragment kind");
 }
 
-MCAsmLayout::MCAsmLayout(MCAssembler &Asm) : Assembler(Asm) {
-  // Compute the section layout order. Virtual sections must go last.
-  for (MCSection &Sec : Asm)
-    if (!Sec.isVirtualSection())
-      SectionOrder.push_back(&Sec);
-  for (MCSection &Sec : Asm)
-    if (Sec.isVirtualSection())
-      SectionOrder.push_back(&Sec);
-}
+MCAsmLayout::MCAsmLayout(MCAssembler &Asm) : Assembler(Asm) {}
 
 // Compute the amount of padding required before the fragment \p F to
 // obey bundling restrictions, where \p FOffset is the fragment's offset in
@@ -951,31 +943,26 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
       errs() << "assembler backend - pre-layout\n--\n";
       dump(); });
 
-  // Create dummy fragments and assign section ordinals.
+  // Assign section ordinals.
   unsigned SectionIndex = 0;
-  for (MCSection &Sec : *this)
+  for (MCSection &Sec : *this) {
     Sec.setOrdinal(SectionIndex++);
 
-  // Assign layout order indices to sections and fragments.
-  for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
-    MCSection *Sec = Layout.getSectionOrder()[i];
-    Sec->setLayoutOrder(i);
-
     // Chain together fragments from all subsections.
-    if (Sec->Subsections.size() > 1) {
+    if (Sec.Subsections.size() > 1) {
       MCDummyFragment Dummy;
       MCFragment *Tail = &Dummy;
-      for (auto &[_, List] : Sec->Subsections) {
+      for (auto &[_, List] : Sec.Subsections) {
         assert(List.Head);
         Tail->Next = List.Head;
         Tail = List.Tail;
       }
-      Sec->Subsections.clear();
-      Sec->Subsections.push_back({0u, {Dummy.getNext(), Tail}});
-      Sec->CurFragList = &Sec->Subsections[0].second;
+      Sec.Subsections.clear();
+      Sec.Subsections.push_back({0u, {Dummy.getNext(), Tail}});
+      Sec.CurFragList = &Sec.Subsections[0].second;
 
       unsigned FragmentIndex = 0;
-      for (MCFragment &Frag : *Sec)
+      for (MCFragment &Frag : Sec)
         Frag.setLayoutOrder(FragmentIndex++);
     }
   }

llvm/lib/MC/MachObjectWriter.cpp

@@ -125,10 +125,10 @@ uint64_t MachObjectWriter::getPaddingSize(const MCAssembler &Asm,
                                           const MCSection *Sec) const {
   uint64_t EndAddr = getSectionAddress(Sec) + Asm.getSectionAddressSize(*Sec);
   unsigned Next = Sec->getLayoutOrder() + 1;
-  if (Next >= Asm.getLayout()->getSectionOrder().size())
+  if (Next >= SectionOrder.size())
     return 0;
 
-  const MCSection &NextSec = *Asm.getLayout()->getSectionOrder()[Next];
+  const MCSection &NextSec = *SectionOrder[Next];
   if (NextSec.isVirtualSection())
     return 0;
   return offsetToAlignment(EndAddr, NextSec.getAlign());
@@ -670,8 +670,24 @@ void MachObjectWriter::computeSymbolTable(
 }
 
 void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm) {
+  // Assign layout order indices to sections.
+  unsigned i = 0;
+  // Compute the section layout order. Virtual sections must go last.
+  for (MCSection &Sec : Asm) {
+    if (!Sec.isVirtualSection()) {
+      SectionOrder.push_back(&Sec);
+      Sec.setLayoutOrder(i++);
+    }
+  }
+  for (MCSection &Sec : Asm) {
+    if (Sec.isVirtualSection()) {
+      SectionOrder.push_back(&Sec);
+      Sec.setLayoutOrder(i++);
+    }
+  }
+
   uint64_t StartAddress = 0;
-  for (const MCSection *Sec : Asm.getLayout()->getSectionOrder()) {
+  for (const MCSection *Sec : SectionOrder) {
     StartAddress = alignTo(StartAddress, Sec->getAlign());
     SectionAddress[Sec] = StartAddress;
     StartAddress += Asm.getSectionAddressSize(*Sec);

llvm/tools/dsymutil/MachOUtils.cpp

@@ -326,14 +326,13 @@ static void transferSegmentAndSections(
 static bool createDwarfSegment(const MCAssembler& Asm,uint64_t VMAddr, uint64_t FileOffset,
                                uint64_t FileSize, unsigned NumSections,
                                 MachObjectWriter &Writer) {
-  auto &Layout = *Asm.getLayout();
   Writer.writeSegmentLoadCommand("__DWARF", NumSections, VMAddr,
                                  alignTo(FileSize, 0x1000), FileOffset,
                                  FileSize, /* MaxProt */ 7,
                                  /* InitProt =*/3);
 
-  for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
-    MCSection *Sec = Layout.getSectionOrder()[i];
+  for (unsigned int i = 0, n = Writer.getSectionOrder().size(); i != n; ++i) {
+    MCSection *Sec = Writer.getSectionOrder()[i];
     if (!Asm.getSectionFileSize(*Sec))
       continue;
 
@@ -491,8 +490,8 @@ bool generateDsymCompanion(
   unsigned NumDwarfSections = 0;
   uint64_t DwarfSegmentSize = 0;
 
-  for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
-    MCSection *Sec = Layout.getSectionOrder()[i];
+  for (unsigned int i = 0, n = Writer.getSectionOrder().size(); i != n; ++i) {
+    MCSection *Sec = Writer.getSectionOrder()[i];
     if (Sec->begin() == Sec->end())
       continue;