[LLVMdev] Processing functions in call graph SCC "order" with function-level analyses

[Félix Cloutier]

You’ll excuse me if I got mixed up somewhere.

The initial problem I had is that adding a required analysis in my CallGraphSCCPass’s getAnalysisUsage caused a runtime error:

> Unable to schedule 'Dominator Tree Construction' required by ‘My Pass'
> Unable to schedule pass
> UNREACHABLE executed at LegacyPassManager.cpp:1264!


My pass is declared in the same program that links against LLVM. The correct way to register these passes appears to use the RegisterPass<T> template, however it does not appear to allow declaring pass dependencies.

At the time, I was advised to bypass the DomTreeWrapperPass and just use DominatorTree::recalculate when I needed it.

It’s with this background that I was saying that the passes are run "manually".

Félix

> Le 2015-05-19 à 12:47:32, John Criswell <jtcriswel at gmail.com> a écrit :
> 
> On 5/19/15 10:04 AM, Félix Cloutier wrote:
>> Thanks John.
>> 
>> Does this solve the problem of analysis availability though? If I still have to run the function analyses manually, I might as well keep rolling with the CallGraphSCCPass. (I probably should have mentioned that this is what I’m using right now.)
> 
> I'm not sure what you mean by "manually."  If you use a ModulePass, you can use the getAnalysis<FunctionPassName>(F) method to get a reference to a function pass.  The ModulePass's getAnalysisUsage() method will need to use addRequired<FunctionPass>() to require each FunctionPass, but I think the PassManager will run the passes automatically as needed.
> 
> Note that you cannot use the PassManager to ensure that certain optimization passes are run before your pass is run.  If you need to run an optimization pass before your pass (e.g., UnifyExitNodes), then you need to tell the PassManager to run it before your pass explicitly.
> 
> Regards,
> 
> John Criswell
> 
>> 
>> Félix
>> 
>>> Le 2015-05-19 à 10:12:32, John Criswell <jtcriswel at gmail.com <mailto:jtcriswel at gmail.com>> a écrit :
>>> 
>>> On 5/18/15 10:45 PM, Félix Cloutier wrote:
>>>> Hi all,
>>>> 
>>>> I have one analysis pass that I want to perform on call graph SCCs. However, for each function in the SCC, I need function-level analyses, like the dominator tree and the memory dependency analysis.
>>>> 
>>>> I’ve been told before <http://stackoverflow.com/questions/30059622/using-dominatortreewrapperpass-in-callgraphsccpass> that these were not available from a CallGraphSCCPass. What would be the best approach for me to access this information? Should I run the passes manually, or is there another, more pass-scheduler-friendly approach?
>>> 
>>> I would write a ModulePass that simply iterates over the call graph.  LLVM provides a CallGraph analysis which one can use to find SCCs; DSA has an analysis called CallTargets which does "real" CallGraph analysis (which means that it tries to reason about function pointers, though I cannot guarantee that its reasoning will be as accurate as you want).
>>> 
>>> If you use a ModulePass, can you analyze any part of the program you like, and you can use FunctionPasses.
>>> 
>>> Regards,
>>> 
>>> John Criswell
>>> 
>>>> 
>>>> Félix
>>>> 
>>>> 
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>>> 
>>> 
>>> -- 
>>> 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>
> 
> 
> -- 
> 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>
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