Re: [RFA] [PATCH] [PR tree-optimization/68619] Avoid direct cfg cleanups in tree-ssa-dom.c [1/3]

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Dec 9, 2015 at 9:31 AM, Jeff Law <law@redhat.com> wrote:
> On 12/08/2015 07:27 AM, Richard Biener wrote:
>>>
>>>
>>> I wonder if it makes more sense to integrate this with the
>>> domwalker itself.  Add a constructor flag to it and do everything
>>> in itself.  By letting the before_dom_children return a taken edge
>>> (or NULL if unknown) it can drive the outgoing edge marking. And
>>> the domwalk worker would simply not recurse to dom children for
>>> unreachable blocks.
>>
>>
>> So interface-wise do
>
> [ ... ]
> Close :-)
>
> If skip_unreachable_blocks is true, then we want the walker to initialize
> EDGE_EXECUTABLE automatically.  So we drop the member initialization and
> constructor body from domwalk.h and instead have a ctor in domwalk.c where
> we can initialize the private members and set EDGE_EXECUTABLE as needed.
>
> My first iteration let the clients clear EDGE_EXECUTABLE as they found
> conditionals that could be optimized.  That was pretty clean and localized
> in sccvn & dom.
>
> If we have the before_dom_children return the taken edge, then we have to
> twiddle all the clients due to the api change in before_dom_children.  .
> There's ~18 in total, so it's not too bad.
>
> 2 of the 18 clearly need to use the skip_unreachable_blocks capability (dom
> and sccvn).  2 others might be able to use it (tree-ssa-pre.c and
> tree-ssa-propagate.c)  I converted dom and sccvn, but not pre and the
> generic propagation engine.
>
> I can submit the iteration which lets clients clear EDGE_EXECUTABLE, or the
> iteration where the clients return the taken edge (or NULL) from the
> before_dom_children callback.
>
> Either is fine with me, so if you have a preference, let me know.

Return the taken edge.

Richard.

> jeff