re PR target/20342 (ICE in spill_failure, at reload1.c:1872)

        PR target/20342
        PR target/20447
        * config/i386/i386.c (print_operand): Handle vector zeros.
        (ix86_split_to_parts): Handle CONST_VECTOR.
        (ix86_hard_regno_mode_ok): Allow MMX modes in general regs.
        (ix86_modes_tieable_p): Use ix86_hard_regno_mode_ok to decide
        what modes to tie for MMX and SSE registers.
        * config/i386/i386.h (MMX_REG_MODE_P): Remove.
        * config/i386/i386.md: Extend move 0 -> xor peephole to apply
        to vector modes as well.
        * config/i386/predicates.md (const0_operand): Handle VOIDmode
        properly as an input mode.

From-SVN: r97663