Mangler: add a beginManglingWithoutPrefix function

Mostly cosmetic, because usually the mangling functions are called only once per mangling instance anyway.

Author: eeckstein

include/swift/Basic/Mangler.h

@@ -94,7 +94,10 @@ class Mangler {
 
   Mangler() : Buffer(Storage) { }
 
-  /// Adds the mangling prefix.
+  /// Begins a new mangling but does not add the mangling prefix.
+  void beginManglingWithoutPrefix();
+
+  /// Begins a new mangling but and adds the mangling prefix.
   void beginMangling();
 
   /// Finish the mangling of the symbol and return the mangled name.

lib/AST/ASTMangler.cpp

@@ -386,13 +386,15 @@ std::string ASTMangler::mangleObjCRuntimeName(const NominalTypeDecl *Nominal) {
 }
 
 std::string ASTMangler::mangleTypeAsContextUSR(const NominalTypeDecl *type) {
+  beginManglingWithoutPrefix();
   llvm::SaveAndRestore<bool> allowUnnamedRAII(AllowNamelessEntities, true);
   appendContext(type);
   return finalize();
 }
 
 std::string ASTMangler::mangleDeclAsUSR(const ValueDecl *Decl,
                                         StringRef USRPrefix) {
+  beginManglingWithoutPrefix();
   llvm::SaveAndRestore<bool> allowUnnamedRAII(AllowNamelessEntities, true);
   Buffer << USRPrefix;
   bindGenericParameters(Decl->getDeclContext());
@@ -419,6 +421,7 @@ std::string ASTMangler::mangleAccessorEntityAsUSR(AccessorKind kind,
                                                   AddressorKind addressorKind,
                                                   const ValueDecl *decl,
                                                   StringRef USRPrefix) {
+  beginManglingWithoutPrefix();
   llvm::SaveAndRestore<bool> allowUnnamedRAII(AllowNamelessEntities, true);
   Buffer << USRPrefix;
   appendAccessorEntity(kind, addressorKind, decl, /*isStatic*/ false);

lib/Basic/Mangler.cpp

@@ -110,12 +110,16 @@ void Mangle::printManglingStats() {
 #endif
 }
 
-void Mangler::beginMangling() {
+void Mangler::beginManglingWithoutPrefix() {
   Storage.clear();
   Substitutions.clear();
   StringSubstitutions.clear();
   Words.clear();
   SubstMerging.clear();
+}
+
+void Mangler::beginMangling() {
+  beginManglingWithoutPrefix();
   Buffer << MANGLING_PREFIX_STR;
 }