COFF: Resolve AlternateNames using weak aliases.

Previously, we use SymbolTable::rename to resolve AlternateName symbols.
This patch is to merge that mechanism with weak aliases, so that we
remove that function.

llvm-svn: 241230

lld/COFF/Driver.cpp

@@ -555,8 +555,6 @@ bool LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
   // A new file may contain a directive section to add new command line options.
   // That's why we have to repeat until converge.)
   for (;;) {
-    size_t Ver = Symtab.getVersion();
-
     // Windows specific -- if entry point is not found,
     // search for its mangled names.
     if (Config->Entry)
@@ -570,22 +568,23 @@ bool LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
 
     // Add weak aliases. Weak aliases is a mechanism to give remaining
     // undefined symbols final chance to be resolved successfully.
-    // This is symbol renaming.
-    for (auto &P : Config->AlternateNames) {
-      StringRef From = P.first;
-      StringRef To = P.second;
-      if (auto EC = Symtab.rename(From, To)) {
-        llvm::errs() << EC.message() << "\n";
-        return false;
-      }
+    for (auto Pair : Config->AlternateNames) {
+      StringRef From = Pair.first;
+      StringRef To = Pair.second;
+      Symbol* Sym = Symtab.findSymbol(From);
+      if (!Sym)
+        continue;
+      if (auto *U = dyn_cast<Undefined>(Sym->Body))
+        if (!U->WeakAlias)
+          U->WeakAlias = Symtab.addUndefined(To);
     }
 
+    if (Symtab.queueEmpty())
+      break;
     if (auto EC = Symtab.run()) {
       llvm::errs() << EC.message() << "\n";
       return false;
     }
-    if (Ver == Symtab.getVersion())
-      break;
   }
 
   // Make sure we have resolved all symbols.

lld/COFF/InputFiles.cpp

@@ -197,7 +197,7 @@ Undefined *ObjectFile::createWeakExternal(COFFSymbolRef Sym, const void *AuxP) {
   COFFObj->getSymbolName(Sym, Name);
   auto *U = new (Alloc) Undefined(Name);
   auto *Aux = (const coff_aux_weak_external *)AuxP;
-  U->WeakAlias = SparseSymbolBodies[Aux->TagIndex];
+  U->WeakAlias = cast<Undefined>(SparseSymbolBodies[Aux->TagIndex]);
   return U;
 }
 

lld/COFF/SymbolTable.cpp

@@ -45,12 +45,11 @@ void SymbolTable::addFile(std::unique_ptr<InputFile> FileP) {
 }
 
 std::error_code SymbolTable::run() {
-  while (!ArchiveQueue.empty() || !ObjectQueue.empty()) {
+  while (!queueEmpty()) {
     if (auto EC = readArchives())
       return EC;
     if (auto EC = readObjects())
       return EC;
-    ++Version;
   }
   return std::error_code();
 }
@@ -112,6 +111,10 @@ std::error_code SymbolTable::readObjects() {
   return std::error_code();
 }
 
+bool SymbolTable::queueEmpty() {
+  return ArchiveQueue.empty() && ObjectQueue.empty();
+}
+
 bool SymbolTable::reportRemainingUndefines() {
   bool Ret = false;
   for (auto &I : Symtab) {
@@ -120,11 +123,12 @@ bool SymbolTable::reportRemainingUndefines() {
     if (!Undef)
       continue;
     StringRef Name = Undef->getName();
-    // The weak alias may have been resovled, so check for that.
-    if (SymbolBody *Alias = Undef->WeakAlias) {
-      if (auto *D = dyn_cast<Defined>(Alias->repl())) {
+    // A weak alias may have been resovled, so check for that. A weak alias
+    // may be an weak alias to other symbol, so check recursively.
+    for (Undefined *U = Undef->WeakAlias; U; U = U->WeakAlias) {
+      if (auto *D = dyn_cast<Defined>(U->repl())) {
         Sym->Body = D;
-        continue;
+        goto next;
       }
     }
     // If we can resolve a symbol by removing __imp_ prefix, do that.
@@ -145,6 +149,7 @@ bool SymbolTable::reportRemainingUndefines() {
       continue;
     }
     Ret = true;
+    next:;
   }
   return Ret;
 }
@@ -253,44 +258,21 @@ void SymbolTable::mangleMaybe(Undefined *U) {
 
   // In Microsoft ABI, a non-member function name is mangled this way.
   std::string Prefix = ("?" + U->getName() + "@@Y").str();
-  for (auto I : Symtab) {
-    StringRef Name = I.first;
-    Symbol *New = I.second;
+  for (auto Pair : Symtab) {
+    StringRef Name = Pair.first;
     if (!Name.startswith(Prefix))
       continue;
-    U->WeakAlias = New->Body;
-    if (auto *L = dyn_cast<Lazy>(New->Body))
-      addMemberFile(L);
+    U->WeakAlias = addUndefined(Name);
     return;
   }
 }
 
 Undefined *SymbolTable::addUndefined(StringRef Name) {
-  auto *U = new (Alloc) Undefined(Name);
-  addSymbol(U);
-  return U;
-}
-
-// Resolve To, and make From an alias to To.
-std::error_code SymbolTable::rename(StringRef From, StringRef To) {
-  // If From is not undefined, do nothing.
-  // Otherwise, rename it to see if To can be resolved instead.
-  auto It = Symtab.find(From);
-  if (It == Symtab.end())
-    return std::error_code();
-  Symbol *Sym = It->second;
-  if (!isa<Undefined>(Sym->Body))
-    return std::error_code();
-  SymbolBody *Body = new (Alloc) Undefined(To);
-  if (auto EC = addSymbol(Body))
-    return EC;
-  SymbolBody *Repl = Body->repl();
-  if (isa<Undefined>(Repl))
-    return std::error_code();
-  Sym->Body = Repl;
-  Body->setBackref(Sym);
-  ++Version;
-  return std::error_code();
+  auto *New = new (Alloc) Undefined(Name);
+  addSymbol(New);
+  if (auto *U = dyn_cast<Undefined>(New->repl()))
+    return U;
+  return New;
 }
 
 void SymbolTable::printMap(llvm::raw_ostream &OS) {

lld/COFF/SymbolTable.h

@@ -46,7 +46,7 @@ public:
   std::error_code run();
   std::error_code readArchives();
   std::error_code readObjects();
-  size_t getVersion() { return Version; }
+  bool queueEmpty();
 
   // Print an error message on undefined symbols.
   bool reportRemainingUndefines();
@@ -85,9 +85,6 @@ public:
   // Creates an Undefined symbol for a given name.
   Undefined *addUndefined(StringRef Name);
 
-  // Rename From -> To in the symbol table.
-  std::error_code rename(StringRef From, StringRef To);
-
   // A list of chunks which to be added to .rdata.
   std::vector<Chunk *> LocalImportChunks;
 
@@ -107,9 +104,6 @@ private:
   std::vector<BitcodeFile *> BitcodeFiles;
   std::unique_ptr<MemoryBuffer> LTOMB;
   llvm::BumpPtrAllocator Alloc;
-
-  // This variable is incremented every time Symtab is updated.
-  size_t Version = 0;
 };
 
 } // namespace coff

lld/COFF/Symbols.h

@@ -249,7 +249,7 @@ public:
   // undefined symbol a second chance if it would remain undefined.
   // If it remains undefined, it'll be replaced with whatever the
   // Alias pointer points to.
-  SymbolBody *WeakAlias = nullptr;
+  Undefined *WeakAlias = nullptr;
 };
 
 // Windows-specific classes.