* rtl.def (CONSTANT_P_RTX): Clarify commentary.
        * expr.c (expand_builtin, case BUILT_IN_CONSTANT_P): Rework to
        consider constant CONSTRUCTOR constant and to defer some cases
        to cse.
        * cse.c (fold_rtx, case CONST): Add handling for CONSTANT_P_RTX.
        * regclass.c (reg_scan_mark_refs, case CONST): Likewise.
Richard Henderson  <rth@cygnus.com>
        * expr.c (init_expr_once): Kill can_handle_constant_p recognition.
        * cse.c (fold_rtx, case 'x'): Remove standalone CONSTANT_P_RTX code.

From-SVN: r24439