[RS6000] Fix 65576 regression

[David Edelsohn]

On Thu, Apr 2, 2015 at 1:22 AM, Alan Modra <amodra@gmail.com> wrote:
> This cures an unrecognizable insn ICE by modifying a predicate of
> extenddftf2_internal (the only place this predicate is used) to ensure
> that rtl optimization passes do not substitute 0.0 for a register with
> known 0.0 value, except when VSX is enabled.  ie. Don't undo the
> necessary register move emitted by the extenddftf2_fprs expander.
> Bootstrapped and regression tested powerpc64le-linux, powerpc64-linux
> and powerpc-linux.  OK to apply?
>
>         PR target/65576
>         PR target/65240
>         * config/rs6000/predicates.md (zero_reg_mem_operand): Exclude
>         0.0 constant unless TARGET_VSX.

This change seems to disable the final alternative in the
extenddftf2_internal pattern.

- David