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

[Jeff Law <law@redhat.com>]

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.

jeff