[PATCH v2 9/9] add short-circuit logic to elfread.c

[Tom Tromey <tromey at redhat dot com>]

If minimal symbols have already been read into a per-BFD object, then
a symbol reader can skip re-reading them.  This changes the ELF reader
to do so.

We only skip the work if the file is ELF+DWARF.  If it has stabs or
mdebug sections, then I think extra information is computed during the
minsym creation pass; and so we must still repeat it.  Eventually even
this will go away, once all symbol types have switched to being
progspace-independent.  In the meantime this has no negative effect --
it is just a missing optimization for a small set of users.

This change also required a somewhat non-obvious change to the OBJSTAT
accounting code.  If a symbol reader skips re-reading minimal symbols,
then the corresponding OBJSTAT will not be updated.  This leads to a
test failure in gdb.base/maint.exp.

After looking at a few fixes for this minor problem, I decided to just
remove minimal symbols from OBJSTATS.  This seemed best to me first
because it eliminates duplicate accounting, and second because the
OBJSTATS were historically wrong here -- including minsyms that were
deleted by de-duplication.

	* elfread.c (elf_read_minimal_symbols): Return early if
	minimal symbols have already been read.  Add "ei" parameter.
	(elf_symfile_read): Call elf_read_minimal_symbols earlier.
	* minsyms.c (prim_record_minimal_symbol_full): Update.
	* objfiles.h (struct objstats) <n_minsyms>: Remove.
	* symmisc.c (print_objfile_statistics): Update.
---
 gdb/elfread.c  | 27 +++++++++++++++++++--------
 gdb/minsyms.c  |  1 -
 gdb/objfiles.h |  1 -
 gdb/symmisc.c  |  4 ++--
 4 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/gdb/elfread.c b/gdb/elfread.c
index 5bf4598..5bb3ddf 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -1076,7 +1076,8 @@ elf_gnu_ifunc_resolver_return_stop (struct breakpoint *b)
    symbols.  */
 
 static void
-elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags)
+elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags,
+			  const struct elfinfo *ei)
 {
   bfd *synth_abfd, *abfd = objfile->obfd;
   struct cleanup *back_to;
@@ -1092,6 +1093,21 @@ elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags)
 			  objfile_name (objfile));
     }
 
+  /* If we already have minsyms, then we can skip some work here.
+     However, if there were stabs or mdebug sections, we go ahead and
+     redo all the work anyway, because the psym readers for those
+     kinds of debuginfo need extra information found here.  This can
+     go away once all types of symbols are in the per-BFD object.  */
+  if (objfile->per_bfd->minsyms_read
+      && ei->stabsect == NULL
+      && ei->mdebugsect == NULL)
+    {
+      if (symtab_create_debug)
+	fprintf_unfiltered (gdb_stdlog,
+			    "... minimal symbols previously read\n");
+      return;
+    }
+
   init_minimal_symbol_collection ();
   back_to = make_cleanup_discard_minimal_symbols ();
 
@@ -1234,16 +1250,11 @@ elf_symfile_read (struct objfile *objfile, int symfile_flags)
   bfd *abfd = objfile->obfd;
   struct elfinfo ei;
 
-  elf_read_minimal_symbols (objfile, symfile_flags);
-
   memset ((char *) &ei, 0, sizeof (ei));
-
-  /* Now process debugging information, which is contained in
-     special ELF sections.  */
-
-  /* We first have to find them...  */
   bfd_map_over_sections (abfd, elf_locate_sections, (void *) & ei);
 
+  elf_read_minimal_symbols (objfile, symfile_flags, &ei);
+
   /* ELF debugging information is inserted into the psymtab in the
      order of least informative first - most informative last.  Since
      the psymtab table is searched `most recent insertion first' this
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 14ca922..21fc468 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -981,7 +981,6 @@ prim_record_minimal_symbol_full (const char *name, int name_len, int copy_name,
   if (!objfile->per_bfd->minsyms_read)
     msym_bunch_index++;
   msym_count++;
-  OBJSTAT (objfile, n_minsyms++);
   return msymbol;
 }
 
diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index deabad4..1064a36 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -145,7 +145,6 @@ struct obj_section
 
 struct objstats
   {
-    int n_minsyms;		/* Number of minimal symbols read */
     int n_psyms;		/* Number of partial symbols read */
     int n_syms;			/* Number of full symbols read */
     int n_stabs;		/* Number of ".stabs" read (if applicable) */
diff --git a/gdb/symmisc.c b/gdb/symmisc.c
index 8d91c8d..4580485 100644
--- a/gdb/symmisc.c
+++ b/gdb/symmisc.c
@@ -111,9 +111,9 @@ print_objfile_statistics (void)
     if (OBJSTAT (objfile, n_stabs) > 0)
       printf_filtered (_("  Number of \"stab\" symbols read: %d\n"),
 		       OBJSTAT (objfile, n_stabs));
-    if (OBJSTAT (objfile, n_minsyms) > 0)
+    if (objfile->per_bfd->minimal_symbol_count > 0)
       printf_filtered (_("  Number of \"minimal\" symbols read: %d\n"),
-		       OBJSTAT (objfile, n_minsyms));
+		       objfile->per_bfd->minimal_symbol_count);
     if (OBJSTAT (objfile, n_psyms) > 0)
       printf_filtered (_("  Number of \"partial\" symbols read: %d\n"),
 		       OBJSTAT (objfile, n_psyms));
-- 
1.8.1.4