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[gdb/symtab] Fix symbol loading performance regression

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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.
This commit is contained in:
Tom de Vries 2019-06-10 20:05:04 +02:00
parent c6a636ce37
commit e99f9db0f5
2 changed files with 16 additions and 6 deletions
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7
gdb/ChangeLog
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@ -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.

15
gdb/symtab.c
View File

@ -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')