[Lldb-commits] [lldb] d28bc54 - [lldb] Remove cache in get_demangled_name_without_arguments

[Raphael Isemann via lldb-commits]

Author: Raphael Isemann
Date: 2021-05-26T18:27:40+02:00
New Revision: d28bc54ff44aad7b080177ef85764d7c5444f031

URL: https://github.com/llvm/llvm-project/commit/d28bc54ff44aad7b080177ef85764d7c5444f031
DIFF: https://github.com/llvm/llvm-project/commit/d28bc54ff44aad7b080177ef85764d7c5444f031.diff

LOG: [lldb] Remove cache in get_demangled_name_without_arguments

This function has a single-value caching based on function local static variables.

This causes two problems:

* There is no synchronization, so this function randomly returns the demangled
  name of other functions that are demangled at the same time.
* The 1-element cache is not very effective (the cache rate is around 0% when
  running the LLDB test suite that calls this function around 30k times).

I would propose just removing it.

To prevent anyone else the git archeology: the static result variables were
originally added as this returned a ConstString reference, but that has since
been changed so that this returns by value.

Reviewed By: #lldb, JDevlieghere, shafik

Differential Revision: https://reviews.llvm.org/D103107

Added: 
    

Modified: 
    lldb/source/Core/Mangled.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Core/Mangled.cpp b/lldb/source/Core/Mangled.cpp
index 3919cb440ab40..82cabc0300113 100644
--- a/lldb/source/Core/Mangled.cpp
+++ b/lldb/source/Core/Mangled.cpp
@@ -35,26 +35,8 @@ static inline bool cstring_is_mangled(llvm::StringRef s) {
   return Mangled::GetManglingScheme(s) != Mangled::eManglingSchemeNone;
 }
 
-static ConstString 
-get_demangled_name_without_arguments(ConstString mangled,
-                                     ConstString demangled) {
-  // This pair is <mangled name, demangled name without function arguments>
-  static std::pair<ConstString, ConstString>
-      g_most_recent_mangled_to_name_sans_args;
-
-  // Need to have the mangled & demangled names we're currently examining as
-  // statics so we can return a const ref to them at the end of the func if we
-  // don't have anything better.
-  static ConstString g_last_mangled;
-  static ConstString g_last_demangled;
-
-  if (mangled && g_most_recent_mangled_to_name_sans_args.first == mangled) {
-    return g_most_recent_mangled_to_name_sans_args.second;
-  }
-
-  g_last_demangled = demangled;
-  g_last_mangled = mangled;
-
+static ConstString GetDemangledNameWithoutArguments(ConstString mangled,
+                                                    ConstString demangled) {
   const char *mangled_name_cstr = mangled.GetCString();
 
   if (demangled && mangled_name_cstr && mangled_name_cstr[0]) {
@@ -73,17 +55,13 @@ get_demangled_name_without_arguments(ConstString mangled,
         if (!cxx_method.GetContext().empty())
           shortname = cxx_method.GetContext().str() + "::";
         shortname += cxx_method.GetBasename().str();
-        ConstString result(shortname.c_str());
-        g_most_recent_mangled_to_name_sans_args.first = mangled;
-        g_most_recent_mangled_to_name_sans_args.second = result;
-        return g_most_recent_mangled_to_name_sans_args.second;
+        return ConstString(shortname);
       }
     }
   }
-
   if (demangled)
-    return g_last_demangled;
-  return g_last_mangled;
+    return demangled;
+  return mangled;
 }
 
 #pragma mark Mangled
@@ -347,7 +325,7 @@ ConstString Mangled::GetName(Mangled::NamePreference preference) const {
   ConstString demangled = GetDemangledName();
 
   if (preference == ePreferDemangledWithoutArguments) {
-    return get_demangled_name_without_arguments(m_mangled, demangled);
+    return GetDemangledNameWithoutArguments(m_mangled, demangled);
   }
   if (preference == ePreferDemangled) {
     // Call the accessor to make sure we get a demangled name in case it hasn't