llvm dev - Dec 2007 - [LLVMdev] Bug 1868: Specifying Pass Orderings

Dear Devang Patel,

In response to your comment on bug 1868, how do I get BottomPass to
requires Pass2 before Pass1?  Is it by reversing the order of the calls
to AU.addRequired()?

-- John T.

-- 
John T. Criswell
jcriswel at bigw.org

"It's today!" said Piglet. "My favorite day," said Pooh.

On Dec 17, 2007, at 1:47 PM, John Criswell wrote:
> Dear Devang Patel,
>
> In response to your comment on bug 1868, how do I get BottomPass to
> requires Pass2 before Pass1?  Is it by reversing the order of the  
> calls
> to AU.addRequired()?
yup :)

-
Devang

Devang Patel wrote:
>
> On Dec 17, 2007, at 2:01 PM, John Criswell wrote:
>
>> Devang Patel wrote:
>>>
>>> On Dec 17, 2007, at 1:47 PM, John Criswell wrote:
>>>
>>>> Dear Devang Patel,
>>>>
>>>> In response to your comment on bug 1868, how do I get
BottomPass to
>>>> requires Pass2 before Pass1?  Is it by reversing the order of
the
>>>> calls
>>>> to AU.addRequired()?
>>>
>>> yup :)
>> So what do I do if both Pass1 and Pass2 preserve nothing?  Is that just
>> unschedule'able with the current Pass Manager?
>
> I am afraid so.
>
>> Both Pass1 and Pass2 are transforms in the original program (the test
>> case is a contrived version to demonstrate the issue).
>
> If they are transforms then technically they are not required by
> BottomPass because they are not analysis.
>
> getAnalysisUsage() interface is not meant to schedule order of
> transformation passes. It is to ensure that analysis required by a
> transformation pass available and up-to-date when transformation pass
> is run.
Okay.  I was afraid of that.  It used to work that way in LLVM 1.9, but
it seems it's changed.
>
> Do you really "require" Pass1 and Pass2 to run BottomPass or do
you
> expect LLVM IR is processed by Pass1 and Pass2 before BottomPass is
> invoked ?
Both, actually.  I'm working on SAFECode, which is built as several
transform passes that run after the automatic pool allocation pass.  I
believe they not only require pool allocation to be run first, but they
also query the pool allocation pass for information on what it has done
(e.g. to determine if a function is a clone of an original function, and
if so, determine what the original function was).

Now that I think about it, I might be able to adjust the SAFECode passes
so that they preserve pool allocation's results.  That might fix it.

So, is there a way for a Pass to specify that other transforms should be
run first, or can that only be done with PassManager.add()?

-- John T.
>
>>  I'm not sure
>> that I can get one of them to preserve the other.
>>
>> -- John T.
>>
>>>
>>> -
>>> Devang
>>>
>>
>>
>> -- 
>> John T. Criswell
>> jcriswel at bigw.org
>>
>> "It's today!" said Piglet. "My favorite day,"
said Pooh.
>>
>>
>
> -
> Devang
>
>

-- 
John T. Criswell
jcriswel at bigw.org

"It's today!" said Piglet. "My favorite day," said Pooh.

On Dec 17, 2007, at 2:25 PM, John Criswell wrote:
> So, is there a way for a Pass to specify that other transforms  
> should be
> run first, or can that only be done with PassManager.add()?

PassManager.add() is the way to go.

If one relies on PassManager to order transformations passes properly  
then we are stepping into "Find optimal ordering of optimization/ 
transformations passes sequence to generate the best code for my  
application" area. I'd prefer to stay out of that, because it is non- 
trivial. Instead, let PassManager users (e.g. llvm-gcc, opt. SAFECode  
driver?) decide the ordering of transformations.

-
Devang