Merge pull request #8985 from ClickHouse/aku/demangle-faster

Avoid extra copying when demangling names.

dbms/src/Functions/demange.cpp

@@ -73,9 +73,15 @@ public:
         for (size_t i = 0; i < input_rows_count; ++i)
         {
             StringRef source = column_concrete->getDataAt(i);
-            int status = 0;
-            std::string demangled = demangle(source.data, status);
-            result_column->insertDataWithTerminatingZero(demangled.data(), demangled.size() + 1);
+            auto demangled = tryDemangle(source.data);
+            if (demangled)
+            {
+                result_column->insertDataWithTerminatingZero(demangled.get(), strlen(demangled.get()));
+            }
+            else
+            {
+                result_column->insertDataWithTerminatingZero(source.data, source.size);
+            }
         }
 
         block.getByPosition(result).column = std::move(result_column);

libs/libcommon/include/common/demangle.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <memory>
 #include <string>
 
 
@@ -14,3 +15,18 @@ inline std::string demangle(const char * name)
     int status = 0;
     return demangle(name, status);
 }
+
+// abi::__cxa_demangle returns a C string of known size that should be deleted
+// with free().
+struct FreeingDeleter
+{
+    template <typename PointerType>
+    void operator() (PointerType ptr)
+    {
+        std::free(ptr);
+    }
+};
+
+typedef std::unique_ptr<char, FreeingDeleter> DemangleResult;
+
+DemangleResult tryDemangle(const char * name);

libs/libcommon/src/demangle.cpp

@@ -10,6 +10,11 @@
 
 #if _MSC_VER || MEMORY_SANITIZER
 
+DemangleResult tryDemangle(const char * name)
+{
+    return DemangleResult{};
+}
+
 std::string demangle(const char * name, int & status)
 {
     status = 0;
@@ -21,28 +26,27 @@ std::string demangle(const char * name, int & status)
 #include <stdlib.h>
 #include <cxxabi.h>
 
-std::string demangle(const char * name, int & status)
+static DemangleResult tryDemangle(const char * name, int & status)
 {
-    std::string res;
-
-    char * demangled_str = abi::__cxa_demangle(name, 0, 0, &status);
-    if (demangled_str)
-    {
-        try
-        {
-            res = demangled_str;
-        }
-        catch (...)
-        {
-            free(demangled_str);
-            throw;
-        }
-        free(demangled_str);
-    }
-    else
-        res = name;
-
-    return res;
+    return DemangleResult(abi::__cxa_demangle(name, nullptr, nullptr, &status));
 }
 
+DemangleResult tryDemangle(const char * name)
+{
+    int status = 0;
+    return tryDemangle(name, status);
+}
+
+std::string demangle(const char * name, int & status)
+{
+    auto result = tryDemangle(name, status);
+    if (result)
+    {
+        return std::string(result.get());
+    }
+
+    return name;
+}
+
+
 #endif