[LLVMdev] Function Pass Manager

[Ivan Llopard]

Hi again,

I come back to this issue with an example. It's a pass which does 
nothing but throw the 'Unable to schedule' error.

namespace {
   struct MyPass : public FunctionPass {
     static char ID; // Pass identification, replacement for typeid
     MyPass() : FunctionPass(ID) {
       initializeMyPassPass(*PassRegistry::getPassRegistry());
     }
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addRequiredID(LoopSimplifyID);
       AU.addPreservedID(LoopSimplifyID);
     }
     virtual bool runOnFunction(Function &F);
   };
}

char MyPass::ID = 0;
INITIALIZE_PASS_BEGIN(MyPass, "mypass", "mypass",
                 false, false)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_END(MyPass, "mypass", "mypass",
                 false, false)

bool MyPass::runOnFunction(Function &F) {
   return MyPass::ID == 0;
}

FunctionPass *llvm::createMyPassPass() {
   return new MyPass();
}

It's a simple FunctionPass requiring a lower level pass, LoopSimplify. I 
wrote this pass among the other llvm passes in Transform/Scalar, it's 
not a dynamic loaded pass.
It's worth to note that if I change this pass to be a ModulePass 
instead, the required pass LoopSimplify is scheduled on-the-fly without 
problems.
Is there any reason to not specialize addLowerLevelRequiredPass() for 
function managers ?

Ivan


Le 23/03/2012 17:00, Ivan Llopard a écrit :
> Hi,
>
> I'm writing a function pass which is dynamically loaded by opt and I 
> need some analysis and passes to be run before my pass:
>
>     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
>       AU.addRequired<LoopInfo>();
>       AU.addPreserved<LoopInfo>();
>       AU.addRequiredID(LoopSimplifyID);
>       AU.addPreservedID(LoopSimplifyID);
>       AU.addRequiredID(LCSSAID);
>       AU.addPreservedID(LCSSAID);
>       AU.addRequired<ScalarEvolution>();
>       AU.addPreserved<ScalarEvolution>();
>     }
>
> When I run it with opt -load, I'm getting the following error:
>
> Unable to schedule 'Canonicalize natural loops' required by 'MyPass'
> Unable to schedule pass
>
> After looking at the pass manager framework, it seems that passes with 
> lower level than FunctionPass (such as LoopPass in my particular case) 
> cannot be scheduled on-the-fly or must be handled by specific function 
> managers. This is not the case for module passes, i.e. module passes 
> requiring function ones. Is it correct ?
>
> In other words, why is addLowerLevelRequiredPass() not specialized for 
> function managers ?
>
> I think I'm misunderstanding the whole thing, is it possible to chain 
> transformation passes from my pass or do I chain them explicitly from 
> the command line ?
>
> Thanks in advance,
>
> Ivan