[Bug middle-end/59049] Two VOIDmode constant in comparison passed to cstoresi4

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59049

--- Comment #8 from Jorn Wolfgang Rennecke <amylaar at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #7)
> That is, sth like
> 
> Index: gcc/tree-ssa-ter.c
> ===================================================================
> --- gcc/tree-ssa-ter.c  (revision 204664)
> +++ gcc/tree-ssa-ter.c  (working copy)
> @@ -438,6 +439,12 @@ ter_is_replaceable_p (gimple stmt)
>           && !is_gimple_val (gimple_assign_rhs1 (stmt)))
>         return false;
>  
> +      /* Do not propagate "modeless" constants - we may end up confusing
> the RTL
> +        expanders.  Leave the optimization to RTL CCP.  */
> +      if (gimple_assign_single_p (stmt)
> +         && CONSTANT_CLASS_P (gimple_assign_rhs1 (stmt)))
> +       return false;
> +
>        return true;
>      }
>    return false;

Constants are often very valuable for rtl expansion, allowing to use
cheaper patterns.
And some constant propagations are impossible in rtl because of mode
oddities.  E.g. when you have a have a mulsidi3 pattern, you generally
have a sign_extend - you can't have a VOIDmode constant inside that.
Therefore, I would rather have the middle-end move the constants
to registers only when necessary to preserve the mode, and preferrably
fold instead in the first place when optimizing.