[RFC] LTO and debug information

[Richard Guenther]

On Sun, 13 Dec 2009, Michael Matz wrote:

> Hi,
> 
> On Sun, 13 Dec 2009, Richard Guenther wrote:
> 
> > *************** free_lang_data_in_decl (tree decl)
> > *** 4380,4408 ****
> >          }
> >      }
> >   
> > !   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;
> > !     }
> 
> Ugh.  If you remove this, add an 'FIXME' comment, in case we ever get the 
> early-debuginfo generation.  We do want to nullify these eventually, and 
> it's sufficiently tricky to free the right things without introducing 
> strange errors so that we don't want to invest the time to find out the 
> details again.  Right now we still remember, but in one year ... :)

I'll replace it with

+ /* ???  We could free non-constant DECL_SIZE, DECL_SIZE_UNIT
+    and DECL_FIELD_OFFSET.  But it's cheap enough to not do
+    that and refrain from adding workarounds to dwarf2out.c  */
+
+ /* DECL_FCONTEXT is only used for debug info generation.  */
+ if (TREE_CODE (decl) == FIELD_DECL
+     && debug_info_level < DINFO_LEVEL_TERSE)
+   DECL_FCONTEXT (decl) = NULL_TREE;
+

the non-constant sizes and offset are gimplified and thus
only a single decl.  IMHO it's not a good idea to make
those types incomplete (even if nothing should really look
at their sizes).  We can deal with DECL_FCONTEXT like with
TYPE_STUB_DECL.

Richard.