On 10/24/2017 02:49 PM, David Malcolm wrote:
> On Tue, 2017-10-24 at 11:40 -0600, Jeff Law wrote:
>> tree-ssa-propagate.c provides a fairly generic engine to propagate
>> values through a lattice while in SSA form.  The engine uses two
>> callbacks to allow passes to provide pass specific handling of
>> statements and phi nodes.
>>
>> The callback mechanism served us well in a C world.  It is however
>> somewhat painful to have state in those callbacks without resorting
>> to
>> global variables or passing around void * objects which contain the
>> class instance pointer.
>>
>> For example, tree-vrp uses the propagation engine to compute global
>> range information.  Its callbacks vrp_visit_stmt and vrp_visit_phi
>> and
>> their children read/modify a variety of tree-vrp.c statics such as
>> vr_data.
>>
>> In some changes I'm working on I'd really like to move vr_data into a
>> distinct class and avoid having direct accesses to the underlying
>> array.
>>
>> So the problem is how are routines like vrp_visit_stmt and
>> vrp_visit_phi
>> and their children supposed to access the class instance?
>>
>> One way would be to just add a void * argument to them and pass the
>> class instance around.  Alternately we could leave the global
>> variable
>> in place and have it set up, checked and wiped clean by the vr_data
>> class's ctor/dtor.  Both are valid and would work, but they're a bit
>> ugly IMHO.
>>
>> This patch takes another approach.  It builds a simple little class
>> around ssa_propagate where the statement and phi visitors are virtual
>> functions.  Thus clients can override the visitors *and* they'll get
>> a
>> class instance pointer.
>>
>> I haven't gone hog wild with C++-ification, basically just enough to
>> get
>> the class around ssa_propagate and its children which are going to
>> need
>> to pass down the class instance to the virtual functions.  There's a
>> lot
>> more that could be done here.
>>
>> As you can see the client side changes are pretty minimal.  They just
>> derive a new class from ssa_propagation_engine to provide their
>> implementations of the statement and phi visitor.  More importantly,
>> they can hang data off that derived class which we'll exploit later.
>>
>> There will be a similar patch for the substitute_and_fold which has
>> callbacks of its own.
>>
>> Bootstrapped and regression tested on x86_64.
>>
>> The ChangeLog makes the patch look huge.  But it's actually
>> relatively
>> small and the client side bits are repetitive.
>>
>> OK for the trunk?
>>
>> Jeff
> 
> Looks like you forgot to attach the patch.
Ugh.  Attached, with the FINAL OVERRIDE addition.


Jeff