[committed, gomp4] Rewrite virtuals into lcssa in transform_to_exit_first_loop_alt

[Richard Biener]

On Thu, Jun 18, 2015 at 9:25 AM, Tom de Vries <Tom_deVries@mentor.com> wrote:
> Hi,
>
> transform_to_exit_first_loop contains the following comment:
> ...
>   /* Make sure that we have phi nodes on exit for all loop header phis
>      (create_parallel_loop requires that).  */
> ...
>
> I ran into a problem where after transform_to_exit_first_loop_alt this
> property does not hold for virtuals, and we run into trouble in
> create_parallel_loop.
>
> The patch ensures that the property holds at the start of
> transform_to_exit_first_loop_alt, which has as effect that:
> - we simplify transform_to_exit_first_loop_alt a bit, and
> - since the property is kept by transform_to_exit_first_loop_alt,
>   the property will be valid after transform_to_exit_first_loop_alt.
>
> Bootstrapped and reg-tested on x86_64.
>
> Committed to gomp-4_0-branch.
>
> OK for trunk?

I once made virtual-operands loop-closed but then somehow I didn't get it
correct (I suppose I ran into the trap of the existing machinery using
update_ssa to update out-of-loop uses) and removed that capability again.

So instead of adding another limited machinery inside tree-parloops
can you instead
make it available from tree-ssa-loop-manip.c, eventually sharing some code?

Other passes would benefit from this as well and it could save some compile-time
as they wouldn't need to rewrite the virtual operands all the time.

Thanks,
Richard.

> Thanks,
> - Tom