[PATCH 2/3] Move file_and_directory to new file and C++-ize

[Tom Tromey <tom@tromey.com>]

This moves file_and_directory to a new file, and then C++-izes it --
replacing direct assignments with methods, and arranging for it to own
any string that must be computed.  Finally, the CU's objfile will only
be used on demand; this is an important property for the new DWARF
indexer's parallel mode.
---
 gdb/dwarf2/file-and-dir.h | 107 ++++++++++++++++++++++++++++++++++++++
 gdb/dwarf2/read.c         |  66 ++++++++---------------
 gdb/dwarf2/read.h         |   1 +
 3 files changed, 129 insertions(+), 45 deletions(-)
 create mode 100644 gdb/dwarf2/file-and-dir.h

diff --git a/gdb/dwarf2/file-and-dir.h b/gdb/dwarf2/file-and-dir.h
new file mode 100644
index 00000000000..64d5a08bf0c
--- /dev/null
+++ b/gdb/dwarf2/file-and-dir.h
@@ -0,0 +1,107 @@
+/* DWARF file and directory
+
+   Copyright (C) 1994-2021 Free Software Foundation, Inc.
+
+   Adapted by Gary Funck (gary@intrepid.com), Intrepid Technology,
+   Inc.  with support from Florida State University (under contract
+   with the Ada Joint Program Office), and Silicon Graphics, Inc.
+   Initial contribution by Brent Benson, Harris Computer Systems, Inc.,
+   based on Fred Fish's (Cygnus Support) implementation of DWARF 1
+   support.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDB_DWARF2_FILE_AND_DIR_H
+#define GDB_DWARF2_FILE_AND_DIR_H
+
+#include "objfiles.h"
+#include <string>
+
+/* The return type of find_file_and_directory.  Note, the enclosed
+   string pointers are only valid while this object is valid.  */
+
+struct file_and_directory
+{
+  file_and_directory (const char *name_, const char *dir_)
+    : name (name_),
+      comp_dir (dir_)
+  {
+  }
+
+  /* Return true if the file name is unknown.  */
+  bool is_unknown () const
+  {
+    return name == nullptr;
+  }
+
+  /* Set the compilation directory.  */
+  void set_comp_dir (std::string &&dir)
+  {
+    comp_dir_storage = std::move (dir);
+    comp_dir = nullptr;
+  }
+
+  /* Fetch the compilation directory.  This may return NULL in some
+     circumstances.  Note that the return value here is not stable --
+     it may change if this object is moved.  To get a stable pointer,
+     you should call intern_comp_dir.  */
+  const char *get_comp_dir () const
+  {
+    if (!comp_dir_storage.empty ())
+      return comp_dir_storage.c_str ();
+    return comp_dir;
+  }
+
+  /* If necessary, intern the compilation directory using OBJFILE's
+     string cache.  Returns the compilation directory.  */
+  const char *intern_comp_dir (struct objfile *objfile)
+  {
+    if (!comp_dir_storage.empty ())
+      {
+	comp_dir = objfile->intern (comp_dir_storage);
+	comp_dir_storage.clear ();
+      }
+    return comp_dir;
+  }
+
+  /* Fetch the filename.  This never returns NULL.  */
+  const char *get_name () const
+  {
+    return name == nullptr ? "<unknown>" : name;
+  }
+
+  /* Set the filename.  */
+  void set_name (const char *name_)
+  {
+    name = name_;
+  }
+
+private:
+
+  /* The filename.  This is never NULL.  */
+  const char *name;
+
+  /* The compilation directory.  NULL if not known.  If we needed to
+     compute a new string, it will be stored in the comp_dir_storage
+     member, and this will be NULL.  Otherwise, points directly to the
+     DW_AT_comp_dir string attribute.  */
+  const char *comp_dir;
+
+  /* The compilation directory, if it needed to be allocated.  */
+  std::string comp_dir_storage;
+};
+
+#endif /* GDB_DWARF2_FILE_AND_DIR_H */
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 3cf0c9ea2a8..5802fc0ef04 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -1206,7 +1206,6 @@ static struct die_info *die_specification (struct die_info *die,
 static line_header_up dwarf_decode_line_header (sect_offset sect_off,
 						struct dwarf2_cu *cu);
 
-struct file_and_directory;
 static void dwarf_decode_lines (struct line_header *,
 				const file_and_directory &,
 				struct dwarf2_cu *, dwarf2_psymtab *,
@@ -1538,21 +1537,6 @@ dwarf2_per_cu_data_deleter::operator() (dwarf2_per_cu_data *data)
     delete data;
 }
 
-/* The return type of find_file_and_directory.  Note, the enclosed
-   string pointers are only valid while this object is valid.  */
-
-struct file_and_directory
-{
-  /* The filename.  This is never NULL.  */
-  const char *name;
-
-  /* The compilation directory.  NULL if not known.  If we needed to
-     compute a new string, it will be stored in the per-BFD string
-     bcache; otherwise, points directly to the DW_AT_comp_dir string
-     attribute owned by the obstack that owns the DIE.  */
-  const char *comp_dir;
-};
-
 static file_and_directory find_file_and_directory (struct die_info *die,
 						   struct dwarf2_cu *cu);
 
@@ -3024,7 +3008,7 @@ dw2_get_file_names_reader (const struct die_reader_specs *reader,
   file_and_directory fnd = find_file_and_directory (comp_unit_die, cu);
 
   int offset = 0;
-  if (strcmp (fnd.name, "<unknown>") != 0)
+  if (fnd.is_unknown ())
     ++offset;
   else if (lh == nullptr)
     return;
@@ -3053,12 +3037,12 @@ dw2_get_file_names_reader (const struct die_reader_specs *reader,
     }
 
   qfn->num_file_names = offset + include_names.size ();
-  qfn->comp_dir = fnd.comp_dir;
+  qfn->comp_dir = fnd.intern_comp_dir (per_objfile->objfile);
   qfn->file_names =
     XOBNEWVEC (&per_objfile->per_bfd->obstack, const char *,
 	       qfn->num_file_names);
   if (offset != 0)
-    qfn->file_names[0] = xstrdup (fnd.name);
+    qfn->file_names[0] = xstrdup (fnd.get_name ());
 
   if (!include_names.empty ())
     memcpy (&qfn->file_names[offset], include_names.data (),
@@ -7005,15 +6989,15 @@ process_psymtab_comp_unit_reader (const struct die_reader_specs *reader,
   gdb::unique_xmalloc_ptr<char> debug_filename;
   static const char artificial[] = "<artificial>";
   file_and_directory fnd = find_file_and_directory (comp_unit_die, cu);
-  if (strcmp (fnd.name, artificial) == 0)
+  if (strcmp (fnd.get_name (), artificial) == 0)
     {
       debug_filename.reset (concat (artificial, "@",
 				    sect_offset_str (per_cu->sect_off),
 				    (char *) NULL));
-      fnd.name = debug_filename.get ();
+      fnd.set_name (debug_filename.get ());
     }
 
-  pst = create_partial_symtab (per_cu, per_objfile, fnd.name);
+  pst = create_partial_symtab (per_cu, per_objfile, fnd.get_name ());
 
   /* This must be done before calling dwarf2_build_include_psymtabs.  */
   pst->dirname = dwarf2_string_attr (comp_unit_die, DW_AT_comp_dir, cu);
@@ -10493,25 +10477,16 @@ producer_is_gcc_lt_4_3 (struct dwarf2_cu *cu)
 static file_and_directory
 find_file_and_directory (struct die_info *die, struct dwarf2_cu *cu)
 {
-  file_and_directory res;
-
   /* Find the filename.  Do not use dwarf2_name here, since the filename
      is not a source language identifier.  */
-  res.name = dwarf2_string_attr (die, DW_AT_name, cu);
-  res.comp_dir = dwarf2_string_attr (die, DW_AT_comp_dir, cu);
-
-  if (res.comp_dir == NULL
-      && producer_is_gcc_lt_4_3 (cu) && res.name != NULL
-      && IS_ABSOLUTE_PATH (res.name))
-    {
-      std::string comp_dir_storage = ldirname (res.name);
-      if (!comp_dir_storage.empty ())
-	res.comp_dir
-	  = cu->per_objfile->objfile->intern (comp_dir_storage.c_str ());
-    }
+  file_and_directory res (dwarf2_string_attr (die, DW_AT_name, cu),
+			  dwarf2_string_attr (die, DW_AT_comp_dir, cu));
 
-  if (res.name == NULL)
-    res.name = "<unknown>";
+  if (res.get_comp_dir () == nullptr
+      && producer_is_gcc_lt_4_3 (cu)
+      && res.get_name () != nullptr
+      && IS_ABSOLUTE_PATH (res.get_name ()))
+    res.set_comp_dir (ldirname (res.get_name ()));
 
   return res;
 }
@@ -10643,7 +10618,7 @@ read_file_scope (struct die_info *die, struct dwarf2_cu *cu)
 
   file_and_directory fnd = find_file_and_directory (die, cu);
 
-  cu->start_symtab (fnd.name, fnd.comp_dir, lowpc);
+  cu->start_symtab (fnd.get_name (), fnd.intern_comp_dir (objfile), lowpc);
 
   gdb_assert (per_objfile->sym_cu == nullptr);
   scoped_restore restore_sym_cu
@@ -20752,7 +20727,7 @@ compute_include_file_name (const struct line_header *lh, const file_entry &fe,
 
   gdb::unique_xmalloc_ptr<char> hold_compare;
   if (!IS_ABSOLUTE_PATH (include_name)
-      && (dir_name != NULL || cu_info.comp_dir != NULL))
+      && (dir_name != nullptr || cu_info.get_comp_dir () != nullptr))
     {
       /* Avoid creating a duplicate name for CU_INFO.
 	 We do this by comparing INCLUDE_NAME and CU_INFO.
@@ -20782,19 +20757,20 @@ compute_include_file_name (const struct line_header *lh, const file_entry &fe,
 	  include_name = name_holder->get ();
 	  include_name_to_compare = include_name;
 	}
-      if (!IS_ABSOLUTE_PATH (include_name) && cu_info.comp_dir != nullptr)
+      if (!IS_ABSOLUTE_PATH (include_name)
+	  && cu_info.get_comp_dir () != nullptr)
 	{
-	  hold_compare.reset (concat (cu_info.comp_dir, SLASH_STRING,
+	  hold_compare.reset (concat (cu_info.get_comp_dir (), SLASH_STRING,
 				      include_name, (char *) NULL));
 	  include_name_to_compare = hold_compare.get ();
 	}
     }
 
   gdb::unique_xmalloc_ptr<char> copied_name;
-  const char *cu_filename = cu_info.name;
-  if (!IS_ABSOLUTE_PATH (cu_filename) && cu_info.comp_dir != nullptr)
+  const char *cu_filename = cu_info.get_name ();
+  if (!IS_ABSOLUTE_PATH (cu_filename) && cu_info.get_comp_dir () != nullptr)
     {
-      copied_name.reset (concat (cu_info.comp_dir, SLASH_STRING,
+      copied_name.reset (concat (cu_info.get_comp_dir (), SLASH_STRING,
 				 cu_filename, (char *) NULL));
       cu_filename = copied_name.get ();
     }
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index fe34e3f95ae..0afcda1c3b0 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -23,6 +23,7 @@
 #include <queue>
 #include <unordered_map>
 #include "dwarf2/comp-unit-head.h"
+#include "dwarf2/file-and-dir.h"
 #include "dwarf2/index-cache.h"
 #include "dwarf2/section.h"
 #include "filename-seen-cache.h"
-- 
2.31.1