Move demangle() from Symbols.cpp to Strings.cpp.

Symbols.cpp contains functions to handle ELF symbols.
demangle() function is essentially a function to work on a
string rather than on an ELF symbol. So Strings.cpp is a
better place to put that function.

This change also make demangle to demangle symbols unconditionally.
Previously, it demangled symbols only when Config->Demangle is true.

llvm-svn: 274804
diff --git a/lld/ELF/Strings.cpp b/lld/ELF/Strings.cpp
index 21d7f42..0c21e88 100644
--- a/lld/ELF/Strings.cpp
+++ b/lld/ELF/Strings.cpp
@@ -11,8 +11,13 @@
 #include "Error.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Config/config.h"
 #include <algorithm>
 
+#ifdef HAVE_CXXABI_H
+#include <cxxabi.h>
+#endif
+
 using namespace llvm;
 using namespace lld;
 using namespace lld::elf;
@@ -68,3 +73,26 @@
   return !S.empty() && isAlpha(S[0]) &&
          std::all_of(S.begin() + 1, S.end(), isAlnum);
 }
+
+// Returns the demangled C++ symbol name for Name.
+std::string elf::demangle(StringRef Name) {
+#if !defined(HAVE_CXXABI_H)
+  return Name;
+#else
+  // __cxa_demangle can be used to demangle strings other than symbol
+  // names which do not necessarily start with "_Z". Name can be
+  // either a C or C++ symbol. Don't call __cxa_demangle if the name
+  // does not look like a C++ symbol name to avoid getting unexpected
+  // result for a C symbol that happens to match a mangled type name.
+  if (!Name.startswith("_Z"))
+    return Name;
+
+  char *Buf =
+      abi::__cxa_demangle(Name.str().c_str(), nullptr, nullptr, nullptr);
+  if (!Buf)
+    return Name;
+  std::string S(Buf);
+  free(Buf);
+  return S;
+#endif
+}