[lld][nfc] Remove lld::demangle() (partial revert of D116279)

{D116279}, in addition to adding support for other demanglers, also
factored out some of the demangling logic. However, I don't think the
abstraction really carries its weight -- after {D135942}, only the ELF
and WASM backends call it with anything other than a non-constant
`shouldDemangle` argument. The COFF and Mach-O backends were already
doing the should-demangle check before calling `demangle()`.

Reviewed By: MaskRay, #lld-macho

Differential Revision: https://reviews.llvm.org/D135943

lld/COFF/Symbols.cpp

@@ -36,9 +36,9 @@ static std::string maybeDemangleSymbol(StringRef symName) {
     StringRef demangleInput = prefixless;
     if (config->machine == I386)
       demangleInput.consume_front("_");
-    std::string demangled = demangle(demangleInput, true);
+    std::string demangled = demangle(demangleInput.str());
     if (demangled != demangleInput)
-      return prefix + demangle(demangleInput, true);
+      return prefix + demangle(demangleInput.str());
     return (prefix + prefixless).str();
   }
   return std::string(symName);

lld/ELF/SymbolTable.cpp

@@ -21,6 +21,7 @@
 #include "lld/Common/Memory.h"
 #include "lld/Common/Strings.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Demangle/Demangle.h"
 
 using namespace llvm;
 using namespace llvm::object;
@@ -145,13 +146,12 @@ StringMap<SmallVector<Symbol *, 0>> &SymbolTable::getDemangledSyms() {
         StringRef name = sym->getName();
         size_t pos = name.find('@');
         if (pos == std::string::npos)
-          demangled = demangle(name, config->demangle);
+          demangled = demangle(name.str());
         else if (pos + 1 == name.size() || name[pos + 1] == '@')
-          demangled = demangle(name.substr(0, pos), config->demangle);
+          demangled = demangle(name.substr(0, pos).str());
         else
-          demangled = (demangle(name.substr(0, pos), config->demangle) +
-                       name.substr(pos))
-                          .str();
+          demangled =
+              (demangle(name.substr(0, pos).str()) + name.substr(pos)).str();
         (*demangledSyms)[demangled].push_back(sym);
       }
   }

lld/ELF/Symbols.cpp

@@ -15,7 +15,7 @@
 #include "Target.h"
 #include "Writer.h"
 #include "lld/Common/ErrorHandler.h"
-#include "lld/Common/Strings.h"
+#include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/Compiler.h"
 #include <cstring>
 
@@ -43,9 +43,16 @@ LLVM_ATTRIBUTE_UNUSED static inline void assertSymbols() {
   AssertSymbol<LazyObject>();
 }
 
+// Returns a symbol for an error message.
+static std::string maybeDemangleSymbol(StringRef symName) {
+  if (elf::config->demangle)
+    return demangle(symName.str());
+  return symName.str();
+}
+
 std::string lld::toString(const elf::Symbol &sym) {
   StringRef name = sym.getName();
-  std::string ret = demangle(name, config->demangle);
+  std::string ret = maybeDemangleSymbol(name);
 
   const char *suffix = sym.getVersionSuffix();
   if (*suffix == '@')

lld/MachO/SymbolTable.cpp

@@ -15,6 +15,7 @@
 #include "SyntheticSections.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
+#include "llvm/Demangle/Demangle.h"
 
 using namespace llvm;
 using namespace lld;

lld/include/lld/Common/Strings.h

@@ -13,19 +13,11 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/GlobPattern.h"
 #include <string>
 #include <vector>
 
 namespace lld {
-// Returns a demangled symbol name. If Name is not a mangled name, it returns
-// name.
-inline std::string demangle(llvm::StringRef symName, bool shouldDemangle) {
-  if (shouldDemangle)
-    return llvm::demangle(symName.str().c_str());
-  return std::string(symName);
-}
 
 llvm::SmallVector<uint8_t, 0> parseHex(llvm::StringRef s);
 bool isValidCIdentifier(llvm::StringRef s);

lld/wasm/Symbols.cpp

@@ -15,7 +15,7 @@
 #include "OutputSegment.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
-#include "lld/Common/Strings.h"
+#include "llvm/Demangle/Demangle.h"
 
 #define DEBUG_TYPE "lld"
 
@@ -34,8 +34,9 @@ std::string maybeDemangleSymbol(StringRef name) {
   // `main` in the case where we need to pass it arguments.
   if (name == "__main_argc_argv")
     return "main";
-
-  return demangle(name, config->demangle);
+  if (wasm::config->demangle)
+    return demangle(name.str());
+  return name.str();
 }
 
 std::string toString(wasm::Symbol::Kind kind) {