[LLVMdev] Make LoopBase inherit from "RegionBase"?

[Tobias Grosser]

On 01/20/10 18:16, Jan Sjodin wrote:
>> I think this should be implemented as a RegionFilter, that checks if a
> 
>> region contains a loop, and that can be asked for further information.
>> In general I do not think this kind of analysis belongs to a region, but
>> as you proposed some kind of filter could be applied. In the short term
>> the passes who need this information could get it on their own.
>>
>>> and a long term consideration about "region pass":
>>>
>>> if we want to integrate region analysis and optimization framework into
>>> llvm,  i think we can use an approach that similar to loop analysis and
>>> optimization: write a class "regionpass" inherit from "pass", and the
>>> corresponding pass manger "RegionPassManager". (a kind of function pass)
>>> if we follow this approach, we need to push the region pass manager into
>>> the llvm pass manager stack.
>>> the first question of this approach is, whats the relationship between
>>> "loop pass manager" and "region pass manager"?
>>>
>>> way 1: make region pass manager below loop pass manager in the stack
>>>
>>> pass manager stack:
>>>
>>> bb pass manager <---top
>>> loop pass manager
>>> region pass manager
>>> function pass manager
>>> ... <---bottom
>>>
>>> in this way the region hierarchy need to be reconstruct when a loop
>>> transform change it.
>>>
>>> way 2: make region pass manager above loop pass manager in the stack
>>>
>>> pass manager stack:
>>>
>>> bb pass manager <---top
>>> region pass manager
>>> loop pass manager
>>> function pass manager
>>>     ... <---bottom
>>>
>>> in this way the loop hierarchy need to be reconstruct when a region pass
>>> change it.
>>>
>>> now we need to choose a way to minimize the loop reconstruction or
>>> region reconstruction. i think that the chance that a region transform
>>> affect the loop structure is smaller, so maybe way 2 is better.
>> This would need some thoughts. Ideal I think we would not order them, but if
>> a region changed, just reconstruct the loops that are in this region and
>> if a
>> loop changed just reconstruct the regions in this loop.
> 
> Imo, a loop is simply a special kind of region, so a "filter" is perhaps the way to
> go if you are interested in loops. Regions containing loops will have to be inspected
> using the PST. 

Except loops that have multiple exits. they are not necessarily (single
entry single exit) region, if the exists do not jump to the same exit bb.