[lld-macho] Don't include zero-size private label symbols in map file

This is also what ld64 does. This will make it easier to compare their
respective map files.

Reviewed By: #lld-macho, thevinster

Differential Revision: https://reviews.llvm.org/D145654

lld/MachO/InputFiles.cpp

@@ -634,12 +634,6 @@ void ObjFile::parseRelocations(ArrayRef<SectionHeader> sectionHeaders,
   }
 }
 
-// Symbols with `l` or `L` as a prefix are linker-private and never appear in
-// the output.
-static bool isPrivateLabel(StringRef name) {
-  return name.startswith("l") || name.startswith("L");
-}
-
 template <class NList>
 static macho::Symbol *createDefined(const NList &sym, StringRef name,
                                     InputSection *isec, uint64_t value,

lld/MachO/MapFile.cpp

@@ -204,9 +204,10 @@ void macho::writeMapFile() {
       if (auto *concatOsec = dyn_cast<ConcatOutputSection>(osec)) {
         for (const InputSection *isec : concatOsec->inputs) {
           for (Defined *sym : isec->symbols)
-            os << format("0x%08llX\t0x%08llX\t[%3u] %s\n", sym->getVA(),
+            if (!(isPrivateLabel(sym->getName()) && sym->size == 0))
-                         sym->size, readerToFileOrdinal[sym->getFile()],
+              os << format("0x%08llX\t0x%08llX\t[%3u] %s\n", sym->getVA(),
-                         sym->getName().str().data());
+                           sym->size, readerToFileOrdinal[sym->getFile()],
+                           sym->getName().str().data());
         }
       } else if (osec == in.cStringSection || osec == in.objcMethnameSection) {
         const auto &liveCStrings = info.liveCStringsForSection.lookup(osec);

lld/MachO/Symbols.h

@@ -383,6 +383,12 @@ inline bool needsBinding(const Symbol *sym) {
     return defined->isExternalWeakDef() || defined->interposable;
   return false;
 }
+
+// Symbols with `l` or `L` as a prefix are linker-private and never appear in
+// the output.
+inline bool isPrivateLabel(StringRef name) {
+  return name.startswith("l") || name.startswith("L");
+}
 } // namespace macho
 
 std::string toString(const macho::Symbol &);

lld/test/MachO/map-file.s

@@ -19,7 +19,7 @@
 
 # CHECK:       Sections:
 # CHECK-NEXT:  Idx  Name         Size     VMA               Type
-# CHECK-NEXT:  0 __text          0000001b [[#%x,TEXT:]]     TEXT
+# CHECK-NEXT:  0 __text          0000001c [[#%x,TEXT:]]     TEXT
 # CHECK-NEXT:  1 __stubs         0000000c [[#%x,STUBS:]]    TEXT
 # CHECK-NEXT:  2 __stub_helper   0000001a [[#%x,HELPER:]]   TEXT
 # CHECK-NEXT:  3 __cstring       0000002b [[#%x,CSTR:]]     DATA
@@ -69,6 +69,7 @@
 # CHECK-NEXT: 0x[[#%X,MAIN]]           0x00000019  [  2] _main
 # CHECK-NEXT: 0x[[#%X,BAR]]            0x00000001  [  2] _bar
 # CHECK-NEXT: 0x[[#%X,FOO]]            0x00000001  [  3] __ZTIN3foo3bar4MethE
+# CHECK-NEXT: 0x[[#%X,FOO+1]]          0x00000001  [  3] ltmp1
 # CHECK-NEXT: 0x[[#%X,STUBS]]          0x00000006  [  5] _baz
 # CHECK-NEXT: 0x[[#%X,STUBS+6]]        0x00000006  [  2] _bar
 # CHECK-NEXT: 0x[[#%X,HELPER]]         0x0000001A  [  0] helper helper
@@ -86,6 +87,7 @@
 # CHECK-NEXT: 0x[[#%X,DYLD]]           0x00000000  [  0] __dyld_private
 # CHECK-NEXT: 0x[[#%X,TLVP]]           0x00000008  [  0] non-lazy-pointer-to-local: _baz_tlv
 # CHECK-NEXT: 0x[[#%X,BSS]]            0x00000001  [  2] _number
+# CHECK-EMPTY:
 
 # MAPFILE: "name":"Total Write map file"
 
@@ -115,11 +117,19 @@
 
 #--- foo.s
 .globl __ZTIN3foo3bar4MethE
+## This should not appear in the map file since it is a zero-size private label
+## symbol.
+ltmp0:
 ## This C++ symbol makes it clear that we do not print the demangled name in
 ## the map file, even if `-demangle` is passed.
 __ZTIN3foo3bar4MethE:
   nop
 
+## This private label symbol will appear in the map file since it has nonzero
+## size.
+ltmp1:
+  nop
+
 .subsections_via_symbols
 
 #--- test.s