[lld-macho][nfc] Move ICF-specific logic into ICF.cpp

[int3]

Summary

This mirrors the code organization in lld/ELF.

[thakis]

LGTM

lld/MachO/ICF.cpp

 #include "ConcatOutputSection.h"
 #include "InputSection.h"
 #include "Symbols.h"
 #include "UnwindInfoSection.h"
 
 #include "lld/Common/CommonLinkerContext.h"
 #include "llvm/Support/Parallel.h"
 #include "llvm/Support/TimeProfiler.h"
+#include "llvm/Support/xxhash.h"
 
 #include <atomic>
 
 using namespace llvm;
 using namespace lld;
 using namespace lld::macho;
 
 class ICF {
void macho::foldIdenticalSections() {
   // coexist with equivalence-class IDs, this is not necessary, but might help
   // someone keep the numbers straight in case we ever need to debug the
   // ICF::segregate()
   std::vector<ConcatInputSection *> hashable;
   uint64_t icfUniqueID = inputSections.size();
   for (ConcatInputSection *isec : inputSections) {
     // FIXME: consider non-code __text sections as hashable?
     bool isHashable = (isCodeSection(isec) || isCfStringSection(isec)) &&
-                      !isec->shouldOmitFromOutput() && isec->isHashableForICF();
+                      !isec->shouldOmitFromOutput() &&
+                      sectionType(isec->getFlags()) == MachO::S_REGULAR;
     if (isHashable) {
       hashable.push_back(isec);
       for (Defined *d : isec->symbols)
         if (d->unwindEntry)
           hashable.push_back(d->unwindEntry);
     } else {
       isec->icfEqClass[0] = ++icfUniqueID;
     }
   }
-  parallelForEach(hashable,
-                  [](ConcatInputSection *isec) { isec->hashForICF(); });
+  parallelForEach(hashable, [](ConcatInputSection *isec) {
+    assert(isec->icfEqClass[0] == 0); // don't overwrite a unique ID!
+    // Turn-on the top bit to guarantee that valid hashes have no collisions
+    // with the small-integer unique IDs for ICF-ineligible sections
+    isec->icfEqClass[0] = xxHash64(isec->data) | (1ull << 63);
+  });
   // Now that every input section is either hashed or marked as unique, run the
   // segregation algorithm to detect foldable subsections.
   ICF(hashable).run();
 }

lld/MachO/InputSection.h

public:
 
   uint64_t getOffset(uint64_t off) const override { return outSecOff + off; }
   uint64_t getVA() const { return InputSection::getVA(0); }
   // ConcatInputSections are entirely live or dead, so the offset is irrelevant.
   bool isLive(uint64_t off) const override { return live; }
   void markLive(uint64_t off) override { live = true; }
   bool isCoalescedWeak() const { return wasCoalesced && symbols.empty(); }
   bool shouldOmitFromOutput() const { return !live || isCoalescedWeak(); }
-  bool isHashableForICF() const;
-  void hashForICF();
   void writeTo(uint8_t *buf);
 
   void foldIdentical(ConcatInputSection *redundant);
   ConcatInputSection *canonical() override {
     return replacement ? replacement : this;
   }
   const InputSection *canonical() const override {
     return replacement ? replacement : this;

lld/MachO/InputSection.cpp

if (subsec.isec == this) {
       break;
     }
   }
   return (toString(getFile()) + ":(" + getName() + "+0x" +
           Twine::utohexstr(off) + ")")
       .str();
 }
 
-// ICF needs to hash any section that might potentially be duplicated so
-// that it can match on content rather than identity.
-bool ConcatInputSection::isHashableForICF() const {
-  switch (sectionType(getFlags())) {
-  case S_REGULAR:
-    return true;
-  case S_CSTRING_LITERALS:
-  case S_4BYTE_LITERALS:
-  case S_8BYTE_LITERALS:
-  case S_16BYTE_LITERALS:
-  case S_LITERAL_POINTERS:
-    llvm_unreachable("found unexpected literal type in ConcatInputSection");
-  case S_ZEROFILL:
-  case S_GB_ZEROFILL:
-  case S_NON_LAZY_SYMBOL_POINTERS:
-  case S_LAZY_SYMBOL_POINTERS:
-  case S_SYMBOL_STUBS:
-  case S_MOD_INIT_FUNC_POINTERS:
-  case S_MOD_TERM_FUNC_POINTERS:
-  case S_COALESCED:
-  case S_INTERPOSING:
-  case S_DTRACE_DOF:
-  case S_LAZY_DYLIB_SYMBOL_POINTERS:
-  case S_THREAD_LOCAL_REGULAR:
-  case S_THREAD_LOCAL_ZEROFILL:
-  case S_THREAD_LOCAL_VARIABLES:
-  case S_THREAD_LOCAL_VARIABLE_POINTERS:
-  case S_THREAD_LOCAL_INIT_FUNCTION_POINTERS:
-    return false;
-  default:
-    llvm_unreachable("Section type");
-  }
-}
-
-void ConcatInputSection::hashForICF() {
-  assert(data.data()); // zeroFill section data has nullptr with non-zero size
-  assert(icfEqClass[0] == 0); // don't overwrite a unique ID!
-  // Turn-on the top bit to guarantee that valid hashes have no collisions
-  // with the small-integer unique IDs for ICF-ineligible sections
-  icfEqClass[0] = xxHash64(data) | (1ull << 63);
-}
-
 void ConcatInputSection::foldIdentical(ConcatInputSection *copy) {
   align = std::max(align, copy->align);
   copy->live = false;
   copy->wasCoalesced = true;
   copy->replacement = this;
 
   // Merge the sorted vectors of symbols together.
   auto it = symbols.begin();