Rename refersToGotEntry needsGot and add comments.

[ruiu]

Summary

This patch addresses a post-commit review comment for r299615.

lld/trunk/ELF/Relocations.cpp

static std::string getLocation(InputSectionBase &S, const SymbolBody &Sym,
   std::string Msg =
       "\n>>> defined in " + toString(Sym.File) + "\n>>> referenced by ";
   std::string Src = S.getSrcMsg<ELFT>(Off);
   if (!Src.empty())
     Msg += Src + "\n>>>               ";
   return Msg + S.getObjMsg<ELFT>(Off);
 }
 
-static bool refersToGotEntry(RelExpr Expr) {
-  return isRelExprOneOf<R_GOT, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE, R_MIPS_GOT_OFF,
-                        R_MIPS_GOT_OFF32, R_GOT_PAGE_PC, R_GOT_PC,
-                        R_GOT_FROM_END>(Expr);
-}
-
 static bool isPreemptible(const SymbolBody &Body, uint32_t Type) {
   // In case of MIPS GP-relative relocations always resolve to a definition
   // in a regular input file, ignoring the one-definition rule. So we,
   // for example, should not attempt to create a dynamic relocation even
   // if the target symbol is preemptible. There are two two MIPS GP-relative
   // relocations R_MIPS_GPREL16 and R_MIPS_GPREL32. But only R_MIPS_GPREL16
   // can be against a preemptible symbol.
   // To get MIPS relocation type we apply 0xff mask. In case of O32 ABI all
if (const auto *DR = dyn_cast<DefinedRegular>(&Body))
     return DR->Section == nullptr; // Absolute symbol.
   return false;
 }
 
 static bool isAbsoluteValue(const SymbolBody &Body) {
   return isAbsolute(Body) || Body.isTls();
 }
 
+// Returns true if Expr refers a PLT entry.
 static bool needsPlt(RelExpr Expr) {
   return isRelExprOneOf<R_PLT_PC, R_PPC_PLT_OPD, R_PLT, R_PLT_PAGE_PC>(Expr);
 }
 
+// Returns true if Expr refers a GOT entry. Note that this function
+// returns false for TLS variables even though they need GOT, because
+// TLS variables uses GOT differently than the regular variables.
+static bool needsGot(RelExpr Expr) {
+  return isRelExprOneOf<R_GOT, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE, R_MIPS_GOT_OFF,
+                        R_MIPS_GOT_OFF32, R_GOT_PAGE_PC, R_GOT_PC,
+                        R_GOT_FROM_END>(Expr);
+}
+
 // True if this expression is of the form Sym - X, where X is a position in the
 // file (PC, or GOT for example).
 static bool isRelExpr(RelExpr Expr) {
   return isRelExprOneOf<R_PC, R_GOTREL, R_GOTREL_FROM_END, R_MIPS_GOTREL,
                         R_PAGE_PC, R_RELAX_GOT_PC>(Expr);
 }
 
 // Returns true if a given relocation can be computed at link-time.
if (needsPlt(Expr) && !Body.isInPlt()) {
         addPltEntry(InX::Iplt, In<ELFT>::IgotPlt, In<ELFT>::RelaIplt,
                     Target->IRelativeRel, Body, true);
       else
         addPltEntry(InX::Plt, In<ELFT>::GotPlt, In<ELFT>::RelaPlt,
                     Target->PltRel, Body, !Preemptible);
     }
 
     // Create a GOT slot if a relocation needs GOT.
-    if (refersToGotEntry(Expr)) {
+    if (needsGot(Expr)) {
       if (Config->EMachine == EM_MIPS) {
         // MIPS ABI has special rules to process GOT entries and doesn't
         // require relocation entries for them. A special case is TLS
         // relocations. In that case dynamic loader applies dynamic
         // relocations to initialize TLS GOT entries.
         // See "Global Offset Table" in Chapter 5 in the following document
         // for detailed description:
         // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
         In<ELFT>::MipsGot->addEntry(Body, Addend, Expr);
         if (Body.isTls() && Body.isPreemptible())
           In<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, In<ELFT>::MipsGot,
                                        Body.getGotOffset(), false, &Body, 0});
       } else if (!Body.isInGot()) {
         addGotEntry<ELFT>(Body, Preemptible);
       }
     }
 
-    if (!needsPlt(Expr) && !refersToGotEntry(Expr) &&
-        isPreemptible(Body, Type)) {
+    if (!needsPlt(Expr) && !needsGot(Expr) && isPreemptible(Body, Type)) {
       // We don't know anything about the finaly symbol. Just ask the dynamic
       // linker to handle the relocation for us.
       if (!Target->isPicRel(Type))
         error("relocation " + toString(Type) +
               " cannot be used against shared object; recompile with -fPIC" +
               getLocation<ELFT>(Sec, Body, Offset));
 
       In<ELFT>::RelaDyn->addReloc(