[LLD] [MachO] Fix GCC build warnings

[mstorsjo]

Summary

This fixes the following warnings produced by GCC 9:

../tools/lld/MachO/Arch/ARM64.cpp: In member function ‘void {anonymous}::OptimizationHintContext::applyAdrpLdr(const lld::macho::OptimizationHint&)’:
../tools/lld/MachO/Arch/ARM64.cpp:448:18: warning: comparison of integer expressions of different signedness: ‘int64_t’ {aka ‘long int’} and ‘uint64_t’ {aka ‘long unsigned int’} [-Wsign-compare]
  448 |   if (ldr.offset != (rel1->referentVA & 0xfff))
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../tools/lld/MachO/UnwindInfoSection.cpp: In function ‘bool canFoldEncoding(compact_unwind_encoding_t)’:
../tools/lld/MachO/UnwindInfoSection.cpp:404:44: warning: comparison between ‘enum<unnamed>’ and ‘enum<unnamed>’ [-Wenum-compare]
  404 |   static_assert(UNWIND_X86_64_MODE_MASK == UNWIND_X86_MODE_MASK, "");
      |                                            ^~~~~~~~~~~~~~~~~~~~
../tools/lld/MachO/UnwindInfoSection.cpp:405:49: warning: comparison between ‘enum<unnamed>’ and ‘enum<unnamed>’ [-Wenum-compare]
  405 |   static_assert(UNWIND_X86_64_MODE_STACK_IND == UNWIND_X86_MODE_STACK_IND, "");
      |                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~

[int3]

lld/MachO/UnwindInfoSection.cpp

404–410

Could we declare the enum to have size uint32_t instead? Or does GCC still warn in that case?

[mstorsjo]

lld/MachO/UnwindInfoSection.cpp

404–410

GCC still warns about that - it's not so much about whether the enums have a defined size or not, but simply that they're values from two different enums - comparing them in most cases would be a bug, while we strictly care only about their numerical value here.

[int3]

lld/MachO/UnwindInfoSection.cpp

404–410

Gotcha. Thanks!

lld/MachO/Arch/ARM64.cpp

if (!parseLdr(ins2, ldr))
     return;
   if (adrp.destRegister != ldr.baseRegister)
     return;
 
   Optional<PerformedReloc> rel1 = findPrimaryReloc(hint.offset0);
   Optional<PerformedReloc> rel2 = findReloc(hint.offset0 + hint.delta[0]);
   if (!rel1 || !rel2)
     return;
-  if (ldr.offset != (rel1->referentVA & 0xfff))
+  if (ldr.offset != static_cast<int64_t>(rel1->referentVA & 0xfff))
     return;
   ldr.offset = rel1->referentVA - rel2->rel.offset - isec->getVA();
   if (!isLiteralLdrEligible(ldr))
     return;
 
   writeNop(buf + hint.offset0);
   writeLiteralLdr(buf + hint.offset0 + hint.delta[0], ldr);
 }

lld/MachO/UnwindInfoSection.cpp

static bool canFoldEncoding(compact_unwind_encoding_t encoding) {
   //  large to encode in the compact unwind encoding.  Instead it requires that
   //  the function contains "subq $nnnnnnnn,RSP" in its prolog.  The compact
   //  encoding contains the offset to the nnnnnnnn value in the function in
   //  UNWIND_X86_64_FRAMELESS_STACK_SIZE.
   // Since this means the unwinder has to look at the `subq` in the function
   // of the unwind info's unwind address, two functions that have identical
   // unwind info can't be folded if it's using this encoding since both
   // entries need unique addresses.
-  static_assert(UNWIND_X86_64_MODE_MASK == UNWIND_X86_MODE_MASK, "");
-  static_assert(UNWIND_X86_64_MODE_STACK_IND == UNWIND_X86_MODE_STACK_IND, "");
+  static_assert(static_cast<uint32_t>(UNWIND_X86_64_MODE_MASK) ==
+                    static_cast<uint32_t>(UNWIND_X86_MODE_MASK),
+                "");
+  static_assert(static_cast<uint32_t>(UNWIND_X86_64_MODE_STACK_IND) ==
+                    static_cast<uint32_t>(UNWIND_X86_MODE_STACK_IND),
+                "");
   if ((target->cpuType == CPU_TYPE_X86_64 || target->cpuType == CPU_TYPE_X86) &&
       (encoding & UNWIND_X86_64_MODE_MASK) == UNWIND_X86_64_MODE_STACK_IND) {
     // FIXME: Consider passing in the two function addresses and getting
     // their two stack sizes off the `subq` and only returning false if they're
     // actually different.
     return false;
   }
   return true;
 }