reland: [Demangle] make llvm::demangle take std::string_view rather than const std::string&

As suggested by @erichkeane in
https://reviews.llvm.org/D141451#inline-1429549

There's potential for a lot more cleanups around these APIs. This is
just a start.

Callers need to be more careful about sub-expressions producing strings
that don't outlast the expression using `llvm::demangle`. Add a
release note.

Differential Revision: https://reviews.llvm.org/D149104

clang/lib/CodeGen/CodeGenAction.cpp

@@ -635,9 +635,8 @@ BackendConsumer::StackSizeDiagHandler(const llvm::DiagnosticInfoStackSize &D) {
     return false;
 
   Diags.Report(*Loc, diag::warn_fe_frame_larger_than)
-      << D.getStackSize()
-      << D.getStackLimit()
-      << llvm::demangle(D.getFunction().getName().str());
+      << D.getStackSize() << D.getStackLimit()
+      << llvm::demangle(D.getFunction().getName());
   return true;
 }
 
@@ -651,7 +650,7 @@ bool BackendConsumer::ResourceLimitDiagHandler(
 
   Diags.Report(*Loc, DiagID)
       << D.getResourceName() << D.getResourceSize() << D.getResourceLimit()
-      << llvm::demangle(D.getFunction().getName().str());
+      << llvm::demangle(D.getFunction().getName());
   return true;
 }
 
@@ -856,7 +855,7 @@ void BackendConsumer::DontCallDiagHandler(const DiagnosticInfoDontCall &D) {
   Diags.Report(LocCookie, D.getSeverity() == DiagnosticSeverity::DS_Error
                               ? diag::err_fe_backend_error_attr
                               : diag::warn_fe_backend_warning_attr)
-      << llvm::demangle(D.getFunctionName().str()) << D.getNote();
+      << llvm::demangle(D.getFunctionName()) << D.getNote();
 }
 
 void BackendConsumer::MisExpectDiagHandler(

lld/COFF/Symbols.cpp

@@ -38,9 +38,9 @@ static std::string maybeDemangleSymbol(const COFFLinkerContext &ctx,
     StringRef demangleInput = prefixless;
     if (ctx.config.machine == I386)
       demangleInput.consume_front("_");
-    std::string demangled = demangle(demangleInput.str());
+    std::string demangled = demangle(demangleInput);
     if (demangled != demangleInput)
-      return prefix + demangle(demangleInput.str());
+      return prefix + demangled;
     return (prefix + prefixless).str();
   }
   return std::string(symName);

lld/ELF/SymbolTable.cpp

@@ -145,13 +145,16 @@ StringMap<SmallVector<Symbol *, 0>> &SymbolTable::getDemangledSyms() {
       if (canBeVersioned(*sym)) {
         StringRef name = sym->getName();
         size_t pos = name.find('@');
+        std::string substr;
         if (pos == std::string::npos)
-          demangled = demangle(name.str());
-        else if (pos + 1 == name.size() || name[pos + 1] == '@')
-          demangled = demangle(name.substr(0, pos).str());
-        else
-          demangled =
-              (demangle(name.substr(0, pos).str()) + name.substr(pos)).str();
+          demangled = demangle(name);
+        else if (pos + 1 == name.size() || name[pos + 1] == '@') {
+          substr = name.substr(0, pos);
+          demangled = demangle(substr);
+        } else {
+          substr = name.substr(0, pos);
+          demangled = (demangle(substr) + name.substr(pos)).str();
+        }
         (*demangledSyms)[demangled].push_back(sym);
       }
   }

lld/ELF/Symbols.cpp

@@ -45,9 +45,7 @@ LLVM_ATTRIBUTE_UNUSED static inline void assertSymbols() {
 
 // Returns a symbol for an error message.
 static std::string maybeDemangleSymbol(StringRef symName) {
-  if (elf::config->demangle)
-    return demangle(symName.str());
-  return symName.str();
+  return elf::config->demangle ? demangle(symName.str()) : symName.str();
 }
 
 std::string lld::toString(const elf::Symbol &sym) {

lld/MachO/Symbols.cpp

@@ -32,7 +32,7 @@ static_assert(sizeof(SymbolUnion) == sizeof(Defined),
 static std::string maybeDemangleSymbol(StringRef symName) {
   if (config->demangle) {
     symName.consume_front("_");
-    return demangle(symName.str());
+    return demangle(symName);
   }
   return symName.str();
 }

lld/wasm/Symbols.cpp

@@ -35,7 +35,7 @@ std::string maybeDemangleSymbol(StringRef name) {
   if (name == "__main_argc_argv")
     return "main";
   if (wasm::config->demangle)
-    return demangle(name.str());
+    return demangle(name);
   return name.str();
 }
 

llvm/docs/ReleaseNotes.rst

@@ -344,6 +344,11 @@ Changes to Sanitizers
 Other Changes
 -------------
 
+* ``llvm::demangle`` now takes a ``std::string_view`` rather than a
+  ``const std::string&``. Be careful passing temporaries into
+  ``llvm::demangle`` that don't outlive the expression using
+  ``llvm::demangle``.
+
 External Open Source Projects Using LLVM 15
 ===========================================
 

llvm/include/llvm/Demangle/Demangle.h

@@ -65,7 +65,7 @@ char *dlangDemangle(std::string_view MangledName);
 /// \param MangledName - reference to string to demangle.
 /// \returns - the demangled string, or a copy of the input string if no
 /// demangling occurred.
-std::string demangle(const std::string &MangledName);
+std::string demangle(std::string_view MangledName);
 
 bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result);
 

llvm/lib/DebugInfo/LogicalView/Readers/LVCodeViewVisitor.cpp

@@ -1605,7 +1605,7 @@ Error LVSymbolVisitor::visitKnownRecord(CVSymbol &Record, ProcSym &Proc) {
 
     // We don't have a way to see if the symbol is compiler generated. Use
     // the linkage name, to detect `scalar deleting destructor' functions.
-    std::string DemangledSymbol = demangle(std::string(LinkageName));
+    std::string DemangledSymbol = demangle(LinkageName);
     if (DemangledSymbol.find("scalar deleting dtor") != std::string::npos) {
       Function->setIsArtificial();
     } else {

llvm/lib/Demangle/Demangle.cpp

@@ -13,27 +13,27 @@
 #include "llvm/Demangle/Demangle.h"
 #include "llvm/Demangle/StringViewExtras.h"
 #include <cstdlib>
-#include <cstring>
+#include <string_view>
 
 using llvm::itanium_demangle::starts_with;
 
-std::string llvm::demangle(const std::string &MangledName) {
+std::string llvm::demangle(std::string_view MangledName) {
   std::string Result;
-  const char *S = MangledName.c_str();
 
   if (nonMicrosoftDemangle(MangledName, Result))
     return Result;
 
-  if (S[0] == '_' && nonMicrosoftDemangle(MangledName.substr(1), Result))
+  if (starts_with(MangledName, '_') &&
+      nonMicrosoftDemangle(MangledName.substr(1), Result))
     return Result;
 
-  if (char *Demangled = microsoftDemangle(S, nullptr, nullptr)) {
+  if (char *Demangled = microsoftDemangle(MangledName, nullptr, nullptr)) {
     Result = Demangled;
     std::free(Demangled);
-    return Result;
+  } else {
+    Result = MangledName;
   }
-
-  return MangledName;
+  return Result;
 }
 
 static bool isItaniumEncoding(std::string_view S) {

llvm/lib/IR/DiagnosticInfo.cpp

@@ -441,8 +441,7 @@ void llvm::diagnoseDontCall(const CallInst &CI) {
 }
 
 void DiagnosticInfoDontCall::print(DiagnosticPrinter &DP) const {
-  DP << "call to " << demangle(getFunctionName().str())
-     << " marked \"dontcall-";
+  DP << "call to " << demangle(getFunctionName()) << " marked \"dontcall-";
   if (getSeverity() == DiagnosticSeverity::DS_Error)
     DP << "error\"";
   else

llvm/tools/llvm-objdump/ELFDump.cpp

@@ -108,10 +108,7 @@ static Error getRelocationValueString(const ELFObjectFile<ELFT> *Obj,
       Expected<StringRef> SymName = SI->getName();
       if (!SymName)
         return SymName.takeError();
-      if (Demangle)
-        Fmt << demangle(std::string(*SymName));
-      else
-        Fmt << *SymName;
+      Fmt << (Demangle ? demangle(*SymName) : *SymName);
     }
   } else {
     Fmt << "*ABS*";

llvm/tools/llvm-objdump/XCOFFDump.cpp

@@ -32,10 +32,8 @@ Error objdump::getXCOFFRelocationValueString(const XCOFFObjectFile &Obj,
   if (!SymNameOrErr)
     return SymNameOrErr.takeError();
 
-  std::string SymName = (*SymNameOrErr).str();
-  if (Demangle)
-    SymName = demangle(SymName);
-
+  std::string SymName =
+      Demangle ? demangle(*SymNameOrErr) : SymNameOrErr->str();
   if (SymbolDescription)
     SymName = getXCOFFSymbolDescription(createSymbolInfo(Obj, *SymI), SymName);
 

llvm/tools/llvm-objdump/llvm-objdump.cpp

@@ -1545,7 +1545,7 @@ static void disassembleObject(const Target *TheTarget, ObjectFile &Obj,
       if (Demangle) {
         // Fetch the demangled names and store them locally.
         for (const SymbolInfoTy &Symbol : SymbolsHere)
-          DemangledSymNamesHere.push_back(demangle(Symbol.Name.str()));
+          DemangledSymNamesHere.push_back(demangle(Symbol.Name));
         // Now we've finished modifying that vector, it's safe to make
         // a vector of StringRefs pointing into it.
         SymNamesHere.insert(SymNamesHere.begin(), DemangledSymNamesHere.begin(),
@@ -1906,9 +1906,8 @@ static void disassembleObject(const Target *TheTarget, ObjectFile &Obj,
               if (TargetSym != nullptr) {
                 uint64_t TargetAddress = TargetSym->Addr;
                 uint64_t Disp = Target - TargetAddress;
-                std::string TargetName = TargetSym->Name.str();
-                if (Demangle)
-                  TargetName = demangle(TargetName);
+                std::string TargetName = Demangle ? demangle(TargetSym->Name)
+                                                  : TargetSym->Name.str();
 
                 *TargetOS << " <";
                 if (!Disp) {
@@ -2508,10 +2507,8 @@ void objdump::printSymbol(const ObjectFile &O, const SymbolRef &Symbol,
 
         if (NameOrErr) {
           outs() << " (csect:";
-          std::string SymName(NameOrErr.get());
-
-          if (Demangle)
-            SymName = demangle(SymName);
+          std::string SymName =
+              Demangle ? demangle(*NameOrErr) : NameOrErr->str();
 
           if (SymbolDescription)
             SymName = getXCOFFSymbolDescription(createSymbolInfo(O, *SymRef),
@@ -2565,10 +2562,7 @@ void objdump::printSymbol(const ObjectFile &O, const SymbolRef &Symbol,
     outs() << " .hidden";
   }
 
-  std::string SymName(Name);
-  if (Demangle)
-    SymName = demangle(SymName);
-
+  std::string SymName = Demangle ? demangle(Name) : Name.str();
   if (O.isXCOFF() && SymbolDescription)
     SymName = getXCOFFSymbolDescription(createSymbolInfo(O, Symbol), SymName);
 

llvm/tools/llvm-readobj/ELFDumper.cpp

@@ -908,7 +908,7 @@ ELFDumper<ELFT>::getShndxTable(const Elf_Shdr *Symtab) const {
 }
 
 static std::string maybeDemangle(StringRef Name) {
-  return opts::Demangle ? demangle(std::string(Name)) : Name.str();
+  return opts::Demangle ? demangle(Name) : Name.str();
 }
 
 template <typename ELFT>

llvm/tools/llvm-tli-checker/llvm-tli-checker.cpp

@@ -107,7 +107,7 @@ static std::string getPrintableName(StringRef Name) {
   std::string OutputName = "'";
   OutputName += Name;
   OutputName += "'";
-  std::string DemangledName(demangle(Name.str()));
+  std::string DemangledName(demangle(Name));
   if (Name != DemangledName) {
     OutputName += " aka ";
     OutputName += DemangledName;