Re: Free more of type decls

[Jan Hubicka <hubicka at ucw dot cz>]

> On Fri, Oct 26, 2018 at 9:12 AM Jan Hubicka <hubicka@ucw.cz> wrote:
> >
> > Hi,
> > this patch frees TYPE_DECL and alignment from TYPE_DECL and also preserves
> > only those TYPE_DECL pointers that are actually used to build ODR type tree.
> >
> > It reduces number of TYPE_DECLs streamed from WPA to ltrans to about 20%
> > and is important for the patch turning types to incomplete types.  Without
> > this change the TREE_TYPE of TYPE_DECL would still point back to complete type
> > and duplicating TYPE_DECLs as well is somewhat laborious.
> 
> So the following is the really important hunk, correct?
> 
> > @@ -5174,7 +5174,7 @@ free_lang_data_in_type (tree type)
> >
> >    /* Drop TYPE_DECLs in TYPE_NAME in favor of the identifier in the
> >       TYPE_DECL if the type doesn't have linkage.  */
> > -  if (! type_with_linkage_p (type))
> > +  if (type != TYPE_MAIN_VARIANT (type) || ! type_with_linkage_p (type))
> >      {
> >        TYPE_NAME (type) = TYPE_IDENTIFIER (type);
> >        TYPE_STUB_DECL (type) = NULL;
> 
> Can you explain why you "free" alignment of TYPE_DECLs?  It's just some
> bits...  does the FE somehow re-use those for sth else?  I wouldn't have
> expected those to be set to anything meaningful.

It is set to 1 for forward declarations and 8 for fully defined types.
Once I start to turn complete types into incomplete they would not match
becaue of this difference.
> 
> I'm not too comfortable with setting TREE_TYPE of a TYPE_DECL to NULL.
> Can we instead use void_type_node?  The tree-inline.c hunk should
> probably test whether DECL_ORIGINAL_TYPE is non-null instead.

void_type_node works too.  I wanted to put in something that will make any
code that relies on it to crash (so I am sure there is none).

Does the following variant look OK?
I am re-testing it.

	* tree.c (free_lang_data_in_decl): Clear alignment and TREE_TYPE
	of TYPE_DECL.
Index: tree.c
===================================================================
--- tree.c	(revision 265522)
+++ tree.c	(working copy)
@@ -5354,6 +5354,10 @@ free_lang_data_in_decl (tree decl)
       DECL_VISIBILITY_SPECIFIED (decl) = 0;
       DECL_INITIAL (decl) = NULL_TREE;
       DECL_ORIGINAL_TYPE (decl) = NULL_TREE;
+      /* Make sure that complete and incomplete types have same TYPE_DECL.
+	 C++ produces different DECL_ALIGN for them.  */
+      SET_DECL_ALIGN (decl, 0);
+      TREE_TYPE (decl) = void_type_node;
     }
   else if (TREE_CODE (decl) == FIELD_DECL)
     DECL_INITIAL (decl) = NULL_TREE;