Introduce objfile::intern

This introduces a string cache on the per-BFD object, replacing the
macro and filename caches.  Both of these caches just store strings,
so this consolidation by itself saves a little memory (about the size
of a bcache per objfile).

Then this patch switches some allocations on the objfile obstack to
use this bcache instead.  This saves more space; and turns out to be a
bit faster as well.

Here are the before and after "maint time" + "maint space" results of
"file ./gdb":

    Command execution time: 4.664021 (cpu), 4.728518 (wall)
    Space used: 39190528 (+29212672 for this command)

    Command execution time: 4.216209 (cpu), 4.107023 (wall)
    Space used: 36667392 (+26689536 for this command)

The main interface to the string cache is a new pair of overloaded
methods, objfile::intern.

gdb/ChangeLog
2020-03-04  Tom Tromey  <tom@tromey.com>

	* symmisc.c (print_symbol_bcache_statistics)
	(print_objfile_statistics): Update.
	* symfile.c (allocate_symtab): Use intern.
	* psymtab.c (partial_symtab::partial_symtab): Use intern.
	* objfiles.h (struct objfile_per_bfd_storage) <filename_cache,
	macro_cache>: Remove.
	<string_cache>: New member.
	(struct objfile) <intern>: New methods.
	* elfread.c (elf_symtab_read): Use intern.
	* dwarf2/read.c (fixup_go_packaging): Intern package name.
	(dwarf2_compute_name, dwarf2_physname)
	(create_dwo_unit_in_dwp_v1, create_dwo_unit_in_dwp_v2): Intern
	names.
	(guess_partial_die_structure_name): Update.
	(partial_die_info::fixup): Intern name.
	(dwarf2_canonicalize_name): Change parameter to objfile.  Intern
	name.
	(dwarf2_name): Intern name.  Update.
	* buildsym.c (buildsym_compunit::get_macro_table): Use
	string_cache.

1 files changed, 18 insertions, 6 deletions

diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index b71a8a9..a568fa4 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -275,13 +275,9 @@ struct objfile_per_bfd_storage
 
   auto_obstack storage_obstack;
 
-  /* Byte cache for file names.  */
+  /* String cache.  */
 
-  gdb::bcache filename_cache;
-
-  /* Byte cache for macros.  */
-
-  gdb::bcache macro_cache;
+  gdb::bcache string_cache;
 
   /* The gdbarch associated with the BFD.  Note that this gdbarch is
      determined solely from BFD information, without looking at target
@@ -533,6 +529,22 @@ public:
     return section_offsets[SECT_OFF_DATA (this)];
   }
 
+  /* Intern STRING and return the unique copy.  The copy has the same
+     lifetime as the per-BFD object.  */
+  const char *intern (const char *str)
+  {
+    return (const char *) per_bfd->string_cache.insert (str, strlen (str) + 1);
+  }
+
+  /* Intern STRING and return the unique copy.  The copy has the same
+     lifetime as the per-BFD object.  */
+  const char *intern (const std::string &str)
+  {
+    return (const char *) per_bfd->string_cache.insert (str.c_str (),
+							str.size () + 1);
+  }
+
+
   /* The object file's original name as specified by the user,
      made absolute, and tilde-expanded.  However, it is not canonicalized
      (i.e., it has not been passed through gdb_realpath).