[Bug rtl-optimization/51933] [4.7 regression] wrong code due to -free

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51933

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|ebotcazou at gcc dot        |unassigned at gcc dot
                   |gnu.org                     |gnu.org

--- Comment #5 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-21 21:27:40 UTC ---
> But then when make_defs_and_copies_lists is called on the QImode -> DImode
> extension, we reach:
>       /* Initialize the work list.  */
>       if (!get_defs (extend_insn, src_reg, &work_list))
>         {
>           VEC_free (rtx, heap, work_list);
>           /* The number of defs being equal to zero can only mean that all the
>              definitions have been previously merged.  */
>           return 2;
>         }
> and because the definition has been changed already.  But nothing performs the
> ext_src_mode check that used to be performed otherwise.
> So we either need to do the src mode checking earlier when we haven't started
> modifying insns (in add_removable_extension?), or we'd need to look even at the
> newly added defs and see what mode they extend from.

OK, I didn't realize that there could be an implicit truncation hidden within
an extension.  And I think that your change to add_removable_extension is fine,
as it still leaves the new flavor of the pass more powerful than the old one.

The other PR is a different problem.