[NFC] Simplifying the condition which kind of MCFragment doesn't need to handle fixup

[Jim]

Summary

1. MCCompactEncodedInstFragment is a subclass of MCEncodedFragment.
2. Add missing kind MCFragment::FT_CVDefRange into MCEncodedFragment's classof.

[efriedma]

Did you audit the other uses of dyn_cast<MCEncodedFragment>

llvm/include/llvm/MC/MCFragment.h

139

This seems obvious given the inheritance structure.

220

MCEncodedFragmentWithFixups::classof is wrong; it allows incorrect casts.

[Jim]

llvm/include/llvm/MC/MCFragment.h

139

MCCVDefRangeFragment inherits MCEncodedFragmentWithFixups.
MCEncodedFragmentWithFixups inherits MCEncodedFragmentWithContents.
MCEncodedFragmentWithContents inherits MCEncodedFragment.

So MCCVDefRangeFragment is kind of MCEncodedFragment.

220

I don't understand why it is wrong? Thanks

[efriedma]

Did you audit the other uses of dyn_cast<MCEncodedFragment>?

llvm/include/llvm/MC/MCFragment.h

220

MCEncodedFragmentWithFixups is a template; the specific fragment kinds only inherit from one specific instantiation of the template.

llvm/include/llvm/MC/MCFragment.h

static bool classof(const MCFragment *F) {
     switch (Kind) {
     default:
       return false;
     case MCFragment::FT_Relaxable:
     case MCFragment::FT_CompactEncodedInst:
     case MCFragment::FT_Data:
     case MCFragment::FT_Dwarf:
     case MCFragment::FT_DwarfFrame:
+    case MCFragment::FT_CVDefRange:
       return true;
     }
   }
 
   /// Should this fragment be placed at the end of an aligned bundle?
   bool alignToBundleEnd() const { return AlignToBundleEnd; }
   void setAlignToBundleEnd(bool V) { AlignToBundleEnd = V; }
 
public:
   const SmallVectorImpl<MCFixup> &getFixups() const { return Fixups; }
 
   fixup_iterator fixup_begin() { return Fixups.begin(); }
   const_fixup_iterator fixup_begin() const { return Fixups.begin(); }
 
   fixup_iterator fixup_end() { return Fixups.end(); }
   const_fixup_iterator fixup_end() const { return Fixups.end(); }
 
   static bool classof(const MCFragment *F) {
     MCFragment::FragmentType Kind = F->getKind();
     return Kind == MCFragment::FT_Relaxable || Kind == MCFragment::FT_Data ||
            Kind == MCFragment::FT_CVDefRange || Kind == MCFragment::FT_Dwarf ||
            Kind == MCFragment::FT_DwarfFrame;
   }
 };
 
 /// Fragment for data and encoded instructions.

llvm/lib/MC/MCAssembler.cpp

void MCAssembler::layout(MCAsmLayout &Layout) {
   // example, to set the index fields in the symbol data).
   getWriter().executePostLayoutBinding(*this, Layout);
 
   // Evaluate and apply the fixups, generating relocation entries as necessary.
   for (MCSection &Sec : *this) {
     for (MCFragment &Frag : Sec) {
       // Data and relaxable fragments both have fixups.  So only process
       // those here.
-      // FIXME: Is there a better way to do this?  MCEncodedFragmentWithFixups
-      // being templated makes this tricky.
-      if (isa<MCEncodedFragment>(&Frag) &&
-          isa<MCCompactEncodedInstFragment>(&Frag))
+      if (isa<MCCompactEncodedInstFragment>(&Frag))
         continue;
-      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag) &&
-          !isa<MCAlignFragment>(&Frag))
+      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCAlignFragment>(&Frag))
         continue;
       ArrayRef<MCFixup> Fixups;
       MutableArrayRef<char> Contents;
       const MCSubtargetInfo *STI = nullptr;
       if (auto *FragWithFixups = dyn_cast<MCDataFragment>(&Frag)) {
         Fixups = FragWithFixups->getFixups();
         Contents = FragWithFixups->getContents();
         STI = FragWithFixups->getSubtargetInfo();