The following draft patch disables the debuginfo disabling when using
-flto or -fwhopr and fixes up things so that for C debugging (mostly)
works.
The main question I have is how to proceed further here (with the
goal that simple debugging should be possible in 4.5).  If we
apply this patch then we expose ICEs when -flto is used in
conjunction with -g because the patch doesn't fix all clashes
between free-lang-data and dwarf2out.  Now I was thinking of
instead of ICEing to sorry () if we ICE, have debuginfo enabled
and had run free-lang-data.  Or to keep -g non-operational for
LTO and add a -glto or -fi-really-want-to-debug option.

Or of course hope I can reasonably fix the ICEs I run into and
deal with the remaining cases as bugs?

The patch has proven useful debugging miscompiles in its current
state already.

Thanks,
Richard.

2009-12-11  Richard Guenther  <rguent...@suse.de>

        * tree.c (free_lang_data_in_binfo): Do not free BINFO_OFFSET
        and BINFO_VPTR_FIELD.
        (free_lang_data_in_decl): Do not free DECL_SIZE_UNIT,
        DECL_SIZE, DECL_FIELD_OFFSET and DECL_FCONTEXT.
        (free_lang_data): Do not disable debuginfo.
        * lto-streamer-out.c (write_symbol_vec): Deal with
        non-constant DECL_SIZE.
        * dwarf2out.c (add_pure_or_virtual_attribute): Check for
        DECL_CONTEXT.
        (gen_type_die_for_member): Test for TYPE_STUB_DECL.
        * opts.c (decode_options): Do not disable var-tracking for lto.

        lto/
        * lto.c (lto_fixup_field_decl): Fixup DECL_FIELD_OFFSET.
        (lto_post_options): Do not disable debuginfo.

Index: gcc/tree.c
===================================================================
*** gcc/tree.c  (revision 155164)
--- gcc/tree.c  (working copy)
*************** free_lang_data_in_binfo (tree binfo)
*** 4152,4164 ****
  
    gcc_assert (TREE_CODE (binfo) == TREE_BINFO);
  
-   BINFO_OFFSET (binfo) = NULL_TREE;
    BINFO_VTABLE (binfo) = NULL_TREE;
-   BINFO_VPTR_FIELD (binfo) = NULL_TREE;
    BINFO_BASE_ACCESSES (binfo) = NULL;
    BINFO_INHERITANCE_CHAIN (binfo) = NULL_TREE;
    BINFO_SUBVTT_INDEX (binfo) = NULL_TREE;
-   BINFO_VPTR_FIELD (binfo) = NULL_TREE;
  
    for (i = 0; VEC_iterate (tree, BINFO_BASE_BINFOS (binfo), i, t); i++)
      free_lang_data_in_binfo (t);
--- 4152,4161 ----
*************** free_lang_data_in_decl (tree decl)
*** 4376,4404 ****
         }
     }
  
!   if (TREE_CODE (decl) == PARM_DECL
!       || TREE_CODE (decl) == FIELD_DECL
!       || TREE_CODE (decl) == RESULT_DECL)
!     {
!       tree unit_size = DECL_SIZE_UNIT (decl);
!       tree size = DECL_SIZE (decl);
!       if ((unit_size && TREE_CODE (unit_size) != INTEGER_CST)
!         || (size && TREE_CODE (size) != INTEGER_CST))
!       {
!         DECL_SIZE_UNIT (decl) = NULL_TREE;
!         DECL_SIZE (decl) = NULL_TREE;
!       }
! 
!       if (TREE_CODE (decl) == FIELD_DECL
!         && DECL_FIELD_OFFSET (decl)
!         && TREE_CODE (DECL_FIELD_OFFSET (decl)) != INTEGER_CST)
!       DECL_FIELD_OFFSET (decl) = NULL_TREE;
! 
!       /* DECL_FCONTEXT is only used for debug info generation.  */
!       if (TREE_CODE (decl) == FIELD_DECL)
!       DECL_FCONTEXT (decl) = NULL_TREE;
!     }
!   else if (TREE_CODE (decl) == FUNCTION_DECL)
      {
        if (gimple_has_body_p (decl))
        {
--- 4373,4379 ----
         }
     }
  
!  if (TREE_CODE (decl) == FUNCTION_DECL)
      {
        if (gimple_has_body_p (decl))
        {
*************** free_lang_data (void)
*** 4973,4985 ****
    diagnostic_finalizer (global_dc) = default_diagnostic_finalizer;
    diagnostic_format_decoder (global_dc) = default_tree_printer;
  
-   /* FIXME. We remove sufficient language data that the debug
-      info writer gets completely confused.  Disable debug information
-      for now.  */
-   debug_info_level = DINFO_LEVEL_NONE;
-   write_symbols = NO_DEBUG;
-   debug_hooks = &do_nothing_debug_hooks;
- 
    return 0;
  }
  
--- 4948,4953 ----
Index: gcc/lto-streamer-out.c
===================================================================
*** gcc/lto-streamer-out.c      (revision 155164)
--- gcc/lto-streamer-out.c      (working copy)
*************** write_symbol_vec (struct lto_streamer_ca
*** 2350,2356 ****
          break;
        }
  
!       if (kind == GCCPK_COMMON && DECL_SIZE (t))
        size = (((uint64_t) TREE_INT_CST_HIGH (DECL_SIZE (t))) << 32)
          | TREE_INT_CST_LOW (DECL_SIZE (t));
        else
--- 2349,2357 ----
          break;
        }
  
!       if (kind == GCCPK_COMMON
!         && DECL_SIZE (t)
!         && TREE_CODE (DECL_SIZE (t)) == INTEGER_CST)
        size = (((uint64_t) TREE_INT_CST_HIGH (DECL_SIZE (t))) << 32)
          | TREE_INT_CST_LOW (DECL_SIZE (t));
        else
Index: gcc/dwarf2out.c
===================================================================
*** gcc/dwarf2out.c     (revision 155164)
--- gcc/dwarf2out.c     (working copy)
*************** add_pure_or_virtual_attribute (dw_die_re
*** 16476,16482 ****
                                   0));
  
        /* GNU extension: Record what type this method came from originally.  */
!       if (debug_info_level > DINFO_LEVEL_TERSE)
        add_AT_die_ref (die, DW_AT_containing_type,
                        lookup_type_die (DECL_CONTEXT (func_decl)));
      }
--- 16476,16483 ----
                                   0));
  
        /* GNU extension: Record what type this method came from originally.  */
!       if (debug_info_level > DINFO_LEVEL_TERSE
!         && DECL_CONTEXT (func_decl))
        add_AT_die_ref (die, DW_AT_containing_type,
                        lookup_type_die (DECL_CONTEXT (func_decl)));
      }
*************** gen_type_die_for_member (tree type, tree
*** 17396,17402 ****
  
    /* If we're trying to avoid duplicate debug info, we may not have
       emitted the member decl for this function.  Emit it now.  */
!   if (TYPE_DECL_SUPPRESS_DEBUG (TYPE_STUB_DECL (type))
        && ! lookup_decl_die (member))
      {
        dw_die_ref type_die;
--- 17397,17404 ----
  
    /* If we're trying to avoid duplicate debug info, we may not have
       emitted the member decl for this function.  Emit it now.  */
!   if (TYPE_STUB_DECL (type)
!       && TYPE_DECL_SUPPRESS_DEBUG (TYPE_STUB_DECL (type))
        && ! lookup_decl_die (member))
      {
        dw_die_ref type_die;
Index: gcc/opts.c
===================================================================
*** gcc/opts.c  (revision 155164)
--- gcc/opts.c  (working copy)
*************** decode_options (unsigned int argc, const
*** 1129,1138 ****
         Otherwise, symbols will be privatized too early, causing link
         errors later.  */
        flag_whole_program = 0;
- 
-       /* FIXME lto.  Disable var-tracking until debug information
-        is properly handled in free_lang_data.  */
-       flag_var_tracking = 0;
  #else
        error ("LTO support has not been enabled in this configuration");
  #endif
--- 1129,1134 ----
Index: gcc/lto/lto.c
===================================================================
*** gcc/lto/lto.c       (revision 155164)
--- gcc/lto/lto.c       (working copy)
*************** static void
*** 1376,1382 ****
  lto_fixup_field_decl (tree t, void *data)
  {
    lto_fixup_decl_common (t, data);
!   gcc_assert (no_fixup_p (DECL_FIELD_OFFSET (t)));
    LTO_FIXUP_SUBTREE (DECL_BIT_FIELD_TYPE (t));
    LTO_FIXUP_SUBTREE (DECL_QUALIFIER (t));
    gcc_assert (no_fixup_p (DECL_FIELD_BIT_OFFSET (t)));
--- 1376,1382 ----
  lto_fixup_field_decl (tree t, void *data)
  {
    lto_fixup_decl_common (t, data);
!   LTO_FIXUP_SUBTREE (DECL_FIELD_OFFSET (t));
    LTO_FIXUP_SUBTREE (DECL_BIT_FIELD_TYPE (t));
    LTO_FIXUP_SUBTREE (DECL_QUALIFIER (t));
    gcc_assert (no_fixup_p (DECL_FIELD_BIT_OFFSET (t)));
Index: gcc/lto/lto-lang.c
===================================================================
*** gcc/lto/lto-lang.c  (revision 155164)
--- gcc/lto/lto-lang.c  (working copy)
*************** lto_handle_option (size_t scode, const c
*** 646,661 ****
  static bool
  lto_post_options (const char **pfilename ATTRIBUTE_UNUSED)
  {
-   /* FIXME lto: We have stripped enough type and other
-      debugging information out of the IR that it may
-      appear ill-formed to dwarf2out, etc.  We must not
-      attempt to generate debug info in lto1.  A more
-      graceful solution would disable the option flags
-      rather than ignoring them, but we'd also have to
-      worry about default debugging options.  */
-   write_symbols = NO_DEBUG;
-   debug_info_level = DINFO_LEVEL_NONE;
- 
    /* -fltrans and -fwpa are mutually exclusive.  Check for that here.  */
    if (flag_wpa && flag_ltrans)
      error ("-fwpa and -fltrans are mutually exclusive");
--- 646,651 ----

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