lld/elf: Extract undefined symbol diagnostic emission into its own function

[thakis]

Summary

Part of PR42260.

lld/ELF/Relocations.cpp

static std::string maybeReportDiscarded(Undefined &Sym) {
   StringRef Signature = File->getShtGroupSignature(ObjSections, ELFSec);
   if (const InputFile *Prevailing =
           Symtab->ComdatGroups.lookup(CachedHashStringRef(Signature)))
     Msg += "\n>>> section group signature: " + Signature.str() +
            "\n>>> prevailing definition is in " + toString(Prevailing);
   return Msg;
 }
 
-// Report an undefined symbol if necessary.
-// Returns true if this function printed out an error message.
-template <class ELFT>
-static bool maybeReportUndefined(Symbol &Sym, InputSectionBase &Sec,
-                                 uint64_t Offset) {
-  if (!Sym.isUndefined() || Sym.isWeak())
-    return false;
-
-  bool CanBeExternal = !Sym.isLocal() && Sym.computeBinding() != STB_LOCAL &&
-                       Sym.Visibility == STV_DEFAULT;
-  if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
-    return false;
+struct UndefinedDiag {
+  Symbol *Sym;
+  InputSectionBase *Sec;
+  uint64_t Offset;
+  bool IsWarning;
+};
 
-  // clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
-  // which references a switch table in a discarded .rodata/.text section. The
-  // .toc and the .rela.toc are incorrectly not placed in the comdat. The ELF
-  // spec says references from outside the group to a STB_LOCAL symbol are not
-  // allowed. Work around the bug.
-  if (Config->EMachine == EM_PPC64 &&
-      cast<Undefined>(Sym).DiscardedSecIdx != 0 && Sec.Name == ".toc")
-    return false;
+template <class ELFT>
+static void reportUndefinedSymbol(const UndefinedDiag &Undef) {
+  Symbol &Sym = *Undef.Sym;
+  InputSectionBase &Sec = *Undef.Sec;
+  uint64_t Offset = Undef.Offset;
 
   auto Visibility = [&]() -> std::string {
     switch (Sym.Visibility) {
     case STV_INTERNAL:
       return "internal ";
     case STV_HIDDEN:
       return "hidden ";
     case STV_PROTECTED:
static void reportUndefinedSymbol(const UndefinedDiag &Undef) {
   if (!Src.empty())
     Msg += Src + "\n>>>               ";
   Msg += Sec.getObjMsg(Offset);
 
   if (Sym.getName().startswith("_ZTV"))
     Msg += "\nthe vtable symbol may be undefined because the class is missing "
            "its key function (see https://lld.llvm.org/missingkeyfunction)";
 
-  if ((Config->UnresolvedSymbols == UnresolvedPolicy::Warn && CanBeExternal) ||
-      Config->NoinhibitExec) {
+  if (Undef.IsWarning)
     warn(Msg);
-    return false;
-  }
+  else
+    error(Msg);
 
-  error(Msg);
-  return true;
+// Report an undefined symbol if necessary.
+// Returns true if this function printed out an error message.
+template <class ELFT>
+static bool maybeReportUndefined(Symbol &Sym, InputSectionBase &Sec,
+                                 uint64_t Offset) {
+  if (!Sym.isUndefined() || Sym.isWeak())
+    return false;
+
+  bool CanBeExternal = !Sym.isLocal() && Sym.computeBinding() != STB_LOCAL &&
+                       Sym.Visibility == STV_DEFAULT;
+  if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
+    return false;
+
+  // clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
+  // which references a switch table in a discarded .rodata/.text section. The
+  // .toc and the .rela.toc are incorrectly not placed in the comdat. The ELF
+  // spec says references from outside the group to a STB_LOCAL symbol are not
+  // allowed. Work around the bug.
+  if (Config->EMachine == EM_PPC64 &&
+      cast<Undefined>(Sym).DiscardedSecIdx != 0 && Sec.Name == ".toc")
+    return false;
+
+
+  UndefinedDiag Undef = { &Sym, &Sec, Offset, /*IsWarning=*/false };
+  if ((Config->UnresolvedSymbols == UnresolvedPolicy::Warn && CanBeExternal) ||
+      Config->NoinhibitExec)
+    Undef.IsWarning = true;
+  reportUndefinedSymbol<ELFT>(Undef);
+  return !Undef.IsWarning;
 }
 
 // MIPS N32 ABI treats series of successive relocations with the same offset
 // as a single relocation. The similar approach used by N64 ABI, but this ABI
 // packs all relocations into the single relocation record. Here we emulate
 // this for the N32 ABI. Iterate over relocation with the same offset and put
 // theirs types into the single bit-set.
 template <class RelTy> static RelType getMipsN32RelType(RelTy *&Rel, RelTy *End) {