[LLVMdev] DominanceFrontier/PostDominanceFrontier for PRE

[Daniel Berlin]

Sigh, the first PRE.cpp URL got munged.
Try
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/PRE.cpp?view=log&pathrev=25348

Also note that though this is an SSA based e-path PRE implementation,
I do *not* believe it is based on the actual SSA e-path PRE thesis i
linked you too.


On Sun, Nov 3, 2013 at 11:33 PM, Daniel Berlin <dberlin at dberlin.org> wrote:
> On Sun, Nov 3, 2013 at 9:19 AM, Christopher Wood
> <christopherwood07 at gmail.com> wrote:
>> On Sun, Nov 3, 2013 at 1:02 AM, Daniel Berlin <dberlin at dberlin.org> wrote:
>>>
>>> As for a "better" way to implement PRE, it depends on what algorithm
>>> you want to use. If you just want to write a PRE pass, that's easy
>>> enough without dominance frontiers.
>>
>>
>> I simply want to write a PRE pass to get a better understanding of the
>> transformation. Any tips on where to get started (beyond the papers you
>> provided) for someone -new- to the game?
>
> Okay, well, SSAPRE is actually a fairly hard paper to implement
> correctly if this is your first go-around.
>
> If you want something that gives you an intro to PRE (though the
> formulation is not "standard" compared to most papers), take a look at
> http://researcher.watson.ibm.com/researcher/files/us-akundu/thesis-mtech.ps
>
> It's implementable, and it'll work, and doesn't require a large amount
> of detail discovery by the user.
>
> Also, if you look at LLVM's svn history, there are old PRE
> implementations that have been deleted:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/PRE.cpp?view=log&pathrev=25348
> (e-path PRE, like the paper above)
>
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVNPRE.cpp?revision=80766&view=markup&pathrev=83192
> (GVNPRE)
>
> Making a worthwhile PRE that is not slow tends to be quite an engineering task.
>
>
>>
>>>
>>>
>>> If you want to implement the original SSAPRE, i suggest looking at
>>> http://jcse.kiise.org/posting/2-3/jcse_2-3_31.pdf
>>>
>>
>> Thanks - I will read through this paper.
>
>>
>> Chris