[lld-macho][nfc] InputSections don't need to track their total # of callsites

[int3]

Summary

... only whether they have more than zero. This simplifies the code slightly.

I've also moved the field into the ConcatInputSection subclass since it doesn't
actually get used by the other InputSections.

[oontvoo]

lg

lld/MachO/ConcatOutputSection.cpp

 // (i.e., ARM) generally does because it has limited-range branch/call
 // instructions, whereas CISC (i.e., x86) generally doesn't. RISC only needs
 // thunks for programs so large that branch source & destination addresses
 // might differ more than the range of branch instruction(s).
 bool ConcatOutputSection::needsThunks() const {
   if (!target->usesThunks())
     return false;
   uint64_t isecAddr = addr;
-  for (InputSection *isec : inputs)
+  for (ConcatInputSection *isec : inputs)
     isecAddr = alignTo(isecAddr, isec->align) + isec->getSize();
   if (isecAddr - addr + in.stubs->getSize() <=
       std::min(target->backwardBranchRange, target->forwardBranchRange))
     return false;
   // Yes, this program is large enough to need thunks.
-  for (InputSection *isec : inputs) {
+  for (ConcatInputSection *isec : inputs) {
     for (Reloc &r : isec->relocs) {
       if (!target->hasAttr(r.type, RelocAttrBits::BRANCH))
         continue;
       auto *sym = r.referent.get<Symbol *>();
       // Pre-populate the thunkMap and memoize call site counts for every
       // InputSection and ThunkInfo. We do this for the benefit of
       // ConcatOutputSection::estimateStubsInRangeVA()
       ThunkInfo &thunkInfo = thunkMap[sym];
       // Knowing ThunkInfo call site count will help us know whether or not we
       // might need to create more for this referent at the time we are
       // estimating distance to __stubs in estimateStubsInRangeVA().
       ++thunkInfo.callSiteCount;
-      // Knowing InputSection call site count will help us avoid work on those
-      // that have no BRANCH relocs.
-      ++isec->callSiteCount;
+      // We can avoid work on InputSections that have no BRANCH relocs.
+      isec->hasCallSites = true;
     }
   }
   return true;
 }
 
 // Since __stubs is placed after __text, we must estimate the address
 // beyond which stubs are within range of a simple forward branch.
 // This is called exactly once, when the last input section has been finalized.
for (size_t callIdx = 0, endIdx = inputs.size(); callIdx < endIdx;
     // contains several branch instructions in succession, then the distance
     // from the current position to the position where the thunks are inserted
     // grows. So leave room for a bunch of thunks.
     unsigned slop = 100 * thunkSize;
     while (finalIdx < endIdx && isecAddr + inputs[finalIdx]->getSize() <
                                     isecVA + forwardBranchRange - slop)
       finalizeOne(inputs[finalIdx++]);
 
-    if (isec->callSiteCount == 0)
+    if (!isec->hasCallSites)
       continue;
 
     if (finalIdx == endIdx && stubsInRangeVA == TargetInfo::outOfRangeVA) {
       // When we have finalized all input sections, __stubs (destined
       // to follow __text) comes within range of forward branches and
       // we can estimate the threshold address after which we can
       // reach any stub with a forward branch. Note that although it
       // sits in the middle of a loop, this code executes only once.

lld/MachO/InputSection.h

public:
   // Whether the data at \p off in this InputSection is live.
   virtual bool isLive(uint64_t off) const = 0;
   virtual void markLive(uint64_t off) = 0;
   virtual InputSection *canonical() { return this; }
 
   OutputSection *parent = nullptr;
 
   uint32_t align = 1;
-  uint32_t callSiteCount : 31;
   // is address assigned?
-  uint32_t isFinal : 1;
+  bool isFinal = false;
 
   ArrayRef<uint8_t> data;
   std::vector<Reloc> relocs;
   // The symbols that belong to this InputSection, sorted by value. With
   // .subsections_via_symbols, there is typically only one element here.
   llvm::TinyPtrVector<Defined *> symbols;
 
 protected:
struct Shared {
     Shared(InputFile *file, StringRef name, StringRef segname, uint32_t flags,
            Kind kind)
         : file(file), name(name), segname(segname), flags(flags),
           sectionKind(kind) {}
   };
 
   InputSection(Kind kind, StringRef segname, StringRef name, InputFile *file,
                ArrayRef<uint8_t> data, uint32_t align, uint32_t flags)
-      : align(align), callSiteCount(0), isFinal(false), data(data),
+      : align(align), data(data),
         shared(make<Shared>(file, name, segname, flags, kind)) {}
 
   InputSection(const InputSection &rhs)
-      : align(rhs.align), callSiteCount(0), isFinal(false), data(rhs.data),
-        shared(rhs.shared) {}
+      : align(rhs.align), data(rhs.data), shared(rhs.shared) {}
 
   const Shared *const shared;
 };
 
 // ConcatInputSections are combined into (Concat)OutputSections through simple
 // concatenation, in contrast with literal sections which may have their
 // contents merged before output.
 class ConcatInputSection final : public InputSection {
public:
 
   // With subsections_via_symbols, most symbols have their own InputSection,
   // and for weak symbols (e.g. from inline functions), only the
   // InputSection from one translation unit will make it to the output,
   // while all copies in other translation units are coalesced into the
   // first and not copied to the output.
   bool wasCoalesced = false;
   bool live = !config->deadStrip;
+  bool hasCallSites = false;
   // This variable has two usages. Initially, it represents the input order.
   // After assignAddresses is called, it represents the offset from the
   // beginning of the output section this section was assigned to.
   uint64_t outSecOff = 0;
 };
 
 // Helper functions to make it easy to sprinkle asserts.