[LLD][COFF][NFC] Store impSym as DefinedImportData in ImportFile.

lld/COFF/InputFiles.cpp

@@ -1059,8 +1059,7 @@ void ImportFile::parse() {
   // address pointed by the __imp_ symbol. (This allows you to call
   // DLL functions just like regular non-DLL functions.)
   if (hdr->getType() == llvm::COFF::IMPORT_CODE)
-    thunkSym = ctx.symtab.addImportThunk(
-        name, cast_or_null<DefinedImportData>(impSym), hdr->Machine);
+    thunkSym = ctx.symtab.addImportThunk(name, impSym, hdr->Machine);
 }
 
 BitcodeFile::BitcodeFile(COFFLinkerContext &ctx, MemoryBufferRef mb,

lld/COFF/InputFiles.h

@@ -346,7 +346,7 @@ class ImportFile : public InputFile {
   static bool classof(const InputFile *f) { return f->kind() == ImportKind; }
   MachineTypes getMachineType() const override;
 
-  Symbol *impSym = nullptr;
+  DefinedImportData *impSym = nullptr;
   Symbol *thunkSym = nullptr;
   std::string dllName;
 

lld/COFF/SymbolTable.cpp

@@ -771,12 +771,12 @@ Symbol *SymbolTable::addCommon(InputFile *f, StringRef n, uint64_t size,
   return s;
 }
 
-Symbol *SymbolTable::addImportData(StringRef n, ImportFile *f) {
+DefinedImportData *SymbolTable::addImportData(StringRef n, ImportFile *f) {
   auto [s, wasInserted] = insert(n, nullptr);
   s->isUsedInRegularObj = true;
   if (wasInserted || isa<Undefined>(s) || s->isLazy()) {
     replaceSymbol<DefinedImportData>(s, n, f);
-    return s;
+    return cast<DefinedImportData>(s);
   }
 
   reportDuplicate(s, f);

lld/COFF/SymbolTable.h

@@ -102,7 +102,7 @@ class SymbolTable {
   Symbol *addCommon(InputFile *f, StringRef n, uint64_t size,
                     const llvm::object::coff_symbol_generic *s = nullptr,
                     CommonChunk *c = nullptr);
-  Symbol *addImportData(StringRef n, ImportFile *f);
+  DefinedImportData *addImportData(StringRef n, ImportFile *f);
   Symbol *addImportThunk(StringRef name, DefinedImportData *s,
                          uint16_t machine);
   void addLibcall(StringRef name);