[gdb/symtab] Fix symbol loading performance regression

The commit "[gdb/symtab] Fix language of duplicate static minimal symbol"
introduces a performance regression, when loading a cc1 executable build with
-O0 -g and gcc 7.4.0.  The performance regression, measured in 'real' time is
about 175%.

The slower execution comes from the fact that the fix in symbol_set_names
makes the call to symbol_find_demangled_name unconditional.

Fix this by reverting the commit, and redoing the fix as follows.

Recapturing the original problem, the first time symbol_set_names is called
with gsymbol.language == lang_auto and linkage_name == "_ZL3foov", the name is
not present in the per_bfd->demangled_names_hash hash table, so
symbol_find_demangled_name is called to demangle the name, after which the
mangled/demangled pair is added to the hashtable.  The call to
symbol_find_demangled_name also sets gsymbol.language to lang_cplus.
The second time symbol_set_names is called with gsymbol.language == lang_auto
and linkage_name == "_ZL3foov", the name is present in the hash table, so the
demangled name from the hash table is used.  However, the language of the
symbol remains lang_auto.

Fix this by adding a field language in struct demangled_name_entry, and using
the field in symbol_set_names to set the language of gsymbol, if necessary.

Tested on x86_64-linux.

gdb/ChangeLog:

2019-06-10  Tom de Vries  <tdevries@suse.de>

	PR symtab/24545
	* symtab.c (struct demangled_name_entry): Add language field.
	(symbol_set_names):  Revert "[gdb/symtab] Fix language of duplicate
	static minimal symbol".  Set and use language field.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d539e813f6805fb617efb97d8bde155a12b4c216..84b3d68051fc8a28d98d9d476c8209b8f8a52849 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2019-06-10  Tom de Vries  <tdevries@suse.de>
+
+       PR symtab/24545
+       * symtab.c (struct demangled_name_entry): Add language field.
+       (symbol_set_names):  Revert "[gdb/symtab] Fix language of duplicate
+       static minimal symbol".  Set and use language field.
+
 2019-06-10  Tom Tromey  <tromey@adacore.com>
 
        * ada-lang.c (_initialize_ada_language): Update help text.

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 130d5cd48fff120e3770f7e4230575f629932cb0..4920d94a247a18daf4e34ab7302de307b74911a5 100644 (file)
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -713,6 +713,7 @@ symbol_set_language (struct general_symbol_info *gsymbol,
 struct demangled_name_entry
 {
   const char *mangled;
+  ENUM_BITFIELD(language) language : LANGUAGE_BITS;
   char demangled[1];
 };
 
@@ -853,11 +854,6 @@ symbol_set_names (struct general_symbol_info *gsymbol,
   else
     linkage_name_copy = linkage_name;
 
-  /* Set the symbol language.  */
-  char *demangled_name_ptr
-    = symbol_find_demangled_name (gsymbol, linkage_name_copy);
-  gdb::unique_xmalloc_ptr<char> demangled_name (demangled_name_ptr);
-
   entry.mangled = linkage_name_copy;
   slot = ((struct demangled_name_entry **)
          htab_find_slot (per_bfd->demangled_names_hash.get (),
@@ -870,6 +866,9 @@ symbol_set_names (struct general_symbol_info *gsymbol,
       || (gsymbol->language == language_go
          && (*slot)->demangled[0] == '\0'))
     {
+      char *demangled_name_ptr
+       = symbol_find_demangled_name (gsymbol, linkage_name_copy);
+      gdb::unique_xmalloc_ptr<char> demangled_name (demangled_name_ptr);
       int demangled_len = demangled_name ? strlen (demangled_name.get ()) : 0;
 
       /* Suppose we have demangled_name==NULL, copy_name==0, and
@@ -906,12 +905,16 @@ symbol_set_names (struct general_symbol_info *gsymbol,
          strcpy (mangled_ptr, linkage_name_copy);
          (*slot)->mangled = mangled_ptr;
        }
+      (*slot)->language = gsymbol->language;
 
       if (demangled_name != NULL)
-       strcpy ((*slot)->demangled, demangled_name.get());
+       strcpy ((*slot)->demangled, demangled_name.get ());
       else
        (*slot)->demangled[0] = '\0';
     }
+  else if (gsymbol->language == language_unknown
+          || gsymbol->language == language_auto)
+    gsymbol->language = (*slot)->language;
 
   gsymbol->name = (*slot)->mangled;
   if ((*slot)->demangled[0] != '\0')