[review v5] Store the mangled name as a string_view

Christian Biesinger (Code Review)
2019-10-21T23:13:16Z

Store the mangled name as a string_view

This should be a bit faster (because we can compare the size first),
but it is also a dependency for the next patch.

(3.47% of gdb startup time is spent in eq_demangled_name_entry when
attaching to Chrome's content_shell binary)

gdb/ChangeLog:

2019-09-27 Christian Biesinger <cbiesinger@google.com>

* symtab.c (struct demangled_name_entry): Change type of mangled
to gdb::string_view.
(hash_demangled_name_entry): Update.
(eq_demangled_name_entry): Update.
(symbol_set_names): Update.

Change-Id: I24711ae2bcaa9e79ca89a6f8fda385d400419175
---
M gdb/symtab.c
1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/gdb/symtab.c b/gdb/symtab.c
index fc736fd..06c0d03 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -68,6 +68,7 @@
#include "filename-seen-cache.h"
#include "arch-utils.h"
#include <algorithm>
+#include "gdbsupport/gdb_string_view.h"
#include "gdbsupport/pathstuff.h"

/* Forward declarations for local functions. */
@@ -713,7 +714,10 @@
/* Objects of this type are stored in the demangled name hash table. */
struct demangled_name_entry
{
- const char *mangled;
+ demangled_name_entry (gdb::string_view mangled_name)
+ : mangled (mangled_name) {}
+
+ gdb::string_view mangled;
ENUM_BITFIELD(language) language : LANGUAGE_BITS;
char demangled[1];
};
@@ -726,7 +730,7 @@
const struct demangled_name_entry *e
= (const struct demangled_name_entry *) data;

- return htab_hash_string (e->mangled);
+ return iterative_hash (e->mangled.data (), e->mangled.length (), 0);
}

/* Equality function for the demangled name hash. */
@@ -739,7 +743,16 @@
const struct demangled_name_entry *db
= (const struct demangled_name_entry *) b;

- return strcmp (da->mangled, db->mangled) == 0;
+ return da->mangled == db->mangled;
+}
+
+static void
+free_demangled_name_entry (void *data)
+{
+ struct demangled_name_entry *e
+ = (struct demangled_name_entry *) data;
+
+ e->~demangled_name_entry();
}

/* Create the hash table used for demangled names. Each hash entry is
@@ -756,7 +769,7 @@

per_bfd->demangled_names_hash.reset (htab_create_alloc
(256, hash_demangled_name_entry, eq_demangled_name_entry,
- NULL, xcalloc, xfree));
+ free_demangled_name_entry, xcalloc, xfree));
}

/* Try to determine the demangled name for a symbol, based on the
@@ -817,7 +830,6 @@
struct demangled_name_entry **slot;
/* A 0-terminated copy of the linkage name. */
const char *linkage_name_copy;
- struct demangled_name_entry entry;

if (gsymbol->language == language_ada)
{
@@ -855,7 +867,7 @@
else
linkage_name_copy = linkage_name;

- entry.mangled = linkage_name_copy;
+ struct demangled_name_entry entry (gdb::string_view (linkage_name_copy, len));
slot = ((struct demangled_name_entry **)
htab_find_slot (per_bfd->demangled_names_hash.get (),
&entry, INSERT));
@@ -888,7 +900,8 @@
obstack_alloc (&per_bfd->storage_obstack,
offsetof (struct demangled_name_entry, demangled)
+ demangled_len + 1));
- (*slot)->mangled = linkage_name;
+ new (*slot) demangled_name_entry
+ (gdb::string_view (linkage_name, len));
}
else
{
@@ -904,7 +917,8 @@
+ len + demangled_len + 2));
mangled_ptr = &((*slot)->demangled[demangled_len + 1]);
strcpy (mangled_ptr, linkage_name_copy);
- (*slot)->mangled = mangled_ptr;
+ new (*slot) demangled_name_entry
+ (gdb::string_view (mangled_ptr, len));
}
(*slot)->language = gsymbol->language;

@@ -917,7 +931,7 @@
|| gsymbol->language == language_auto)
gsymbol->language = (*slot)->language;

- gsymbol->name = (*slot)->mangled;
+ gsymbol->name = (*slot)->mangled.data ();
if ((*slot)->demangled[0] != '\0')
symbol_set_demangled_name (gsymbol, (*slot)->demangled,
&per_bfd->storage_obstack);