[LLVMdev] Bug 1868: Specifying Pass Orderings

[John Criswell]

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.