[ELF] Change some global pointers to unique_ptr

Currently the singleton `config` is assigned by `config = make<Configuration>()`
and (if `canExitEarly` is false) destroyed by `lld::freeArena`.

`make<Configuration>` allocates a stab with `malloc(4096)`. This both wastes
memory and bloats the executable (every type instantiates `BumpPtrAllocator`
which costs more than 1KiB code on x86-64).

(No need to worry about `clang::no_destroy`. Regular invocations (`canExitEarly`
is true) call `_Exit` via llvm::sys::Process::ExitNoCleanup.)

Reviewed By: lichray

Differential Revision: https://reviews.llvm.org/D116143

lld/ELF/Config.h

@@ -22,6 +22,7 @@
 #include "llvm/Support/GlobPattern.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include <atomic>
+#include <memory>
 #include <vector>
 
 namespace lld {
@@ -343,7 +344,7 @@ struct Configuration {
 };
 
 // The only instance of Configuration struct.
-extern Configuration *config;
+extern std::unique_ptr<Configuration> config;
 
 // The first two elements of versionDefinitions represent VER_NDX_LOCAL and
 // VER_NDX_GLOBAL. This helper returns other elements.

lld/ELF/Driver.cpp

@@ -71,8 +71,8 @@ using namespace llvm::support;
 using namespace lld;
 using namespace lld::elf;
 
-Configuration *elf::config;
-LinkerDriver *elf::driver;
+std::unique_ptr<Configuration> elf::config;
+std::unique_ptr<LinkerDriver> elf::driver;
 
 static void setConfigs(opt::InputArgList &args);
 static void readConfigs(opt::InputArgList &args);
@@ -111,10 +111,10 @@ bool elf::link(ArrayRef<const char *> args, bool canExitEarly,
   errorHandler().exitEarly = canExitEarly;
   stderrOS.enable_colors(stderrOS.has_colors());
 
-  config = make<Configuration>();
-  driver = make<LinkerDriver>();
-  script = make<LinkerScript>();
-  symtab = make<SymbolTable>();
+  config = std::make_unique<Configuration>();
+  driver = std::make_unique<LinkerDriver>();
+  script = std::make_unique<LinkerScript>();
+  symtab = std::make_unique<SymbolTable>();
 
   partitions = {Partition()};
 

lld/ELF/Driver.h

@@ -22,7 +22,7 @@
 namespace lld {
 namespace elf {
 
-extern class LinkerDriver *driver;
+extern std::unique_ptr<class LinkerDriver> driver;
 
 class LinkerDriver {
 public:

lld/ELF/LinkerScript.cpp

@@ -47,7 +47,7 @@ using namespace llvm::support::endian;
 using namespace lld;
 using namespace lld::elf;
 
-LinkerScript *elf::script;
+std::unique_ptr<LinkerScript> elf::script;
 
 static bool isSectionPrefix(StringRef prefix, StringRef name) {
   return name.consume_front(prefix) && (name.empty() || name[0] == '.');

lld/ELF/LinkerScript.h

@@ -366,7 +366,7 @@ public:
   std::vector<const InputSectionBase *> orphanSections;
 };
 
-extern LinkerScript *script;
+extern std::unique_ptr<LinkerScript> script;
 
 } // end namespace elf
 } // end namespace lld

lld/ELF/SymbolTable.cpp

@@ -29,7 +29,7 @@ using namespace llvm::ELF;
 using namespace lld;
 using namespace lld::elf;
 
-SymbolTable *elf::symtab;
+std::unique_ptr<SymbolTable> elf::symtab;
 
 void SymbolTable::wrap(Symbol *sym, Symbol *real, Symbol *wrap) {
   // Redirect __real_foo to the original foo and foo to the original __wrap_foo.

lld/ELF/SymbolTable.h

@@ -91,7 +91,7 @@ private:
   llvm::Optional<llvm::StringMap<std::vector<Symbol *>>> demangledSyms;
 };
 
-extern SymbolTable *symtab;
+extern std::unique_ptr<SymbolTable> symtab;
 
 } // namespace elf
 } // namespace lld