[llvm-dev] pass invalidation

[Mehdi Amini via llvm-dev]

> On Jun 19, 2016, at 8:05 AM, John Criswell <jtcriswel at gmail.com> wrote:
> 
> On 6/19/16 4:28 AM, Mehdi Amini via llvm-dev wrote:
>> 
>>> On Jun 18, 2016, at 10:44 PM, Yuxi Chen via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>> 
>>> Hi All, 
>>> 
>>> When I use llvm, I encounter a problem like "unable to schedule pass A required by C"
>>> I investigated deeper. It's like:
>>> I have three passes, say A, B, C(all are on function level)
>>> A would modify IR code. (change instruction order)
>>> 
>>> For pass B, 
>>> I would use the result of pass A, I use addRequired<B>(), and &getAnalysis<B>(), it works. 
>>> 
>>> void getAnalysisUsage(AU){
>>> AU.addRequired<A>();
>>> }
>>> 
>>> 
>>> For pass C, it will use the results of pass A and B. 
>>> I use the way as used for pass B, but it failed, even for LoopInfo analysis pass(which is the built-in analysis pass).
>>> void getAnalysisUsage(AU){
>>> AU.addRequired<A>();
>>> AU.addRequired<B>();
>>> }
>>> 
>>> 
>>> It seems because A would modify IR code, so for pass C, I need first load pass A then pass B, otherwise it will be invalidated. 
>>> However, when I change the using order, I still got error "unable to schedule pass A required by C".
>>> 
>>> Does anyone encounter the same problem before and have a solution?
>>> Any help is appreciated. 
>> 
>> Depending on other transformations isn’t recommended, and isn’t supported by the soon-new-passmanager I believe.
>> The expectation is that the passes are added in order to the pass manager by the client.
> 
> Depending on transformation passes isn't supported by the legacy PassManager, either. 

Really? What about LCSSA for example? My impression was that the legacy PM does not make any distinction between transformations and analysis.

-- 
Mehdi

> Occasionally some passes can get away with it, but it often results in unschedule-able pass pipelines as above.
> 
> If your transform pass does something to the code, other passes should either infer what it did by examining the IR.  the IR contains the definitive information about the program (because it is the program).
> 
> Alternatively, you could create an analysis pass upon which both your transform and analysis passes depend.  The transform pass would update this new analysis pass with information on what it transformed; your later analysis passes could then query this information.  This approach is fragile, but it could work.
> 
> Regards,
> 
> John Criswell
> 
>> 
>> In you case, I expect that it would “work” by removing the dependency from C to A. If C requires B and B requires A, by scheduling C you’ll get A, B, C in sequence.
>> 
>> — 
>> Mehdi
>> 
>> 
>> 
>>> 
>>> Best,
>>> Yuxi
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>> 
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
> 
> -- 
> John Criswell
> Assistant Professor
> Department of Computer Science, University of Rochester
> http://www.cs.rochester.edu/u/criswell <http://www.cs.rochester.edu/u/criswell>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160619/b222398f/attachment.html>