[RFA] Minor cleanup to VRP/EVRP handling of deferred edge/switch optimization

[Jeff Law]

On 9/20/18 6:51 AM, Richard Biener wrote:
> On Mon, Sep 17, 2018 at 4:50 PM Jeff Law <law@redhat.com> wrote:
>>
>> This is a relatively minor cleanup that I should have caught last cycle,
>> but somehow missed.
>>
>> We have two structures TO_REMOVE_EDGES and TO_UPDATE_SWITCH_STMTS which
>> are used by the VRP/EVRP code to record edges to remove and switch
>> statements that need updating.
>>
>> They are currently implemented as globals within tree-vrp.c with an
>> appropriate extern within tree-vrp.h.
>>
>> The code to walk those vectors was only implemented in VRP, but we can
>> (and do) add to those vectors within EVRP.   So EVRP would detect
>> certain edges as dead or switches that were needed simplification, but
>> they were left as-is because EVRP never walked the vectors to do the
>> necessary cleanup.
>>
>> This change pushes the vectors into the vr_values structure.  They're
>> initialized in the ctor and we verify they're properly cleaned up in the
>> dtor.  This obviously avoids the global object carrying state, but also
>> catches cases where we record that an optimization was possible but
>> failed to update the IL appropriately.
>>
>> As a side effect, we don't need to bother with initializing and wiping
>> EDGE_IGNORE for jump threading in VRP.  We just mark the appropriate
>> edges at the same time we put them in TO_REMOVE_EDGES within vr_values.
>>
>> vrp113.c is an example of where EVRP detected optimizations should be
>> possible, but failed to update the IL.  Given the test really wanted to
>> check VRP's behavior, I've disabled EVRP for that test.
>>
>> Bootstrapped and regression tested on x86_64-linux-gnu.
>>
>> OK for the trunk?
> 
> OK.  Maybe you can duplicate vrp113.c to also have a EVRP testing variant
> of this functionality?
Sure.  I'd pondered doing something like that anyway.  We can verify
that EVRP collapses the test and that we do not trigger the "did you
fail to clean up properly" assert.

jeff