[lld/mac] Move output segment rename logic into OutputSegment

[thakis]

Summary

No behavior change. The motivation is that segment$start$ can
create section-less segments, and this makes a corner case in
the interaction between segment$start and -rename_segment
in the upcoming segment$start patch.

[int3]

lgtm

lld/MachO/ConcatOutputSection.cpp

while (t < te && (i == ie || thunks[t]->outSecOff < inputs[i]->outSecOff)) {
       ++t;
     }
   }
 }
 
 void ConcatOutputSection::finalizeFlags(InputSection *input) {
   switch (sectionType(input->getFlags())) {
   default /*type-unspec'ed*/:
-    // FIXME: Add additional logics here when supporting emitting obj files.
+    // FIXME: Add additional logic here when supporting emitting obj files.
     break;
   case S_4BYTE_LITERALS:
   case S_8BYTE_LITERALS:
   case S_16BYTE_LITERALS:
   case S_CSTRING_LITERALS:
   case S_ZEROFILL:
   case S_LAZY_SYMBOL_POINTERS:
   case S_MOD_TERM_FUNC_POINTERS:
if (!osec)
     osec = make<ConcatOutputSection>(names.second);
   return osec;
 }
 
 NamePair macho::maybeRenameSection(NamePair key) {
   auto newNames = config->sectionRenameMap.find(key);
   if (newNames != config->sectionRenameMap.end())
     return newNames->second;
-  auto newName = config->segmentRenameMap.find(key.first);
-  if (newName != config->segmentRenameMap.end())
-    return std::make_pair(newName->second, key.second);
   return key;
 }

lld/MachO/OutputSegment.cpp

 void macho::sortOutputSegments() {
   llvm::stable_sort(outputSegments,
                     compareByOrder<OutputSegment *>(segmentOrder));
 }
 
 static DenseMap<StringRef, OutputSegment *> nameToOutputSegment;
 std::vector<OutputSegment *> macho::outputSegments;
 
+static StringRef maybeRenameSegment(StringRef name) {
+  auto newName = config->segmentRenameMap.find(name);
+  if (newName != config->segmentRenameMap.end())
+    return newName->second;
+  return name;
+}
+
 OutputSegment *macho::getOrCreateOutputSegment(StringRef name) {
+  name = maybeRenameSegment(name);
+
   OutputSegment *&segRef = nameToOutputSegment[name];
   if (segRef)
     return segRef;
 
   segRef = make<OutputSegment>();
   segRef->name = name;
   segRef->maxProt = maxProt(name);
   segRef->initProt = initProt(name);
 
   outputSegments.push_back(segRef);
   return segRef;
 }

lld/test/MachO/rename.s

 # RUN:     -rename_section __FROM_SECT __from_sect __TO_SECT __to_sect \
 # RUN:   -o %t.dylib %t/small.o
 # RUN: llvm-otool -l %t.dylib | FileCheck --check-prefix=SECTSEGYES %s
 # SECTSEGYES:      Section
 # SECTSEGYES-NEXT:   sectname __text
 # SECTSEGYES-NEXT:    segname __TEXT
 # SECTSEGYES:      Section
 # SECTSEGYES-NEXT:   sectname __to_sect
-# SECTSEGYES-NEXT:    segname __TO_SECT
-## FIXME: ^ This should use __SEG like ld64 does.
+# SECTSEGYES-NEXT:    segname __SEG
 ## ...but rename_segment has no effect if it doesn't match the name after
 ## rename_section is applied.
 # RUN: %lld -dylib \
 # RUN:     -rename_section __FROM_SECT __from_sect __TO_SECT __to_sect \
 # RUN:     -rename_segment __FROM_SECT __SEG \
 # RUN:   -o %t.dylib %t/small.o
 # RUN: llvm-otool -l %t.dylib | FileCheck --check-prefix=SECTSEGSOME %s
 # SECTSEGSOME:      Section