[LLVMdev] problem with analysis required

[John Criswell]

Kshitiz Garg wrote:
> Hello,
>     I was trying to get the loop info in a module pass to be able to
> iterate over the loops int the module itself. Since my pass requires
> to make module level changes including adding new types to module
> hence a looppass cannot be used here.
> I am getting the following error on running opt.
>
> opt: /root/llvm-2.4/include/llvm/PassAnalysisSupport.h:199:
> AnalysisType& llvm::Pass::getAnalysisID(const llvm::PassInfo*) const
> [with AnalysisType = llvm::LoopInfo]: Assertion `ResultPass &&
> "getAnalysis*() called on an analysis that was not " "'required' by
> pass!"' failed.
>
> <snip_gdb_trace>
> #4  0x083006f2 in llvm::Pass::getAnalysisID<llvm::LoopInfo> (this=0x86cfc48,
>     PI=0x86cbfe0) at /root/llvm-2.4/include/llvm/PassAnalysisSupport.h:197
> #5  0x083007aa in llvm::Pass::getAnalysis<llvm::LoopInfo> (this=0x86cfc48)
>     at /root/llvm-2.4/include/llvm/PassAnalysisSupport.h:186
> #6  0x0056e1c0 in runOnModule (this=0x86cfc48, M=@0x86cfeb8) at timing.cpp:167
> </snip_gdb_trace>
> gdb backtrace points to the following statement in the runOnModule method;
> Loopinfo * LI = &getAnalysis<LoopInfo>();
>   
I believe the problem here is that you need to specify the function for
which you want loop information in the above call, i.e.:

Loopinfo * LI = &getAnalysis<LoopInfo>(F)

... where F is either a pointer to the Function or is a reference to the
Function (I don't recall the details off-hand; see
http://llvm.org/docs/WritingAnLLVMPass.html#getAnalysis for more
information.

You said that your pass needs to make some global modification to the
Module.  In some cases, you can still write your pass as a FunctionPass;
simply put the code that changes global Module information into the
doInitialization() or doFinalization() methods.

-- John T.


> following is the content of the getAnalysis Usage method.
>
>  void getAnalysisUsage(AnalysisUsage &AU) const {
>             AU.addRequired<LoopInfo> ();
>             AU.addPreserved<LoopInfo> ();
> }
>
> I picked this from the LPPassManager class which has a similar
> structure and its runOnFunction iterates over loop list from LoopInfo.
>
> I think I am missing some line to add. Can someone please point out
> the cause of the error??
>
> Thanks
> regards,
> Kshitiz
> --
> Kshitiz Garg
> Graduate Student
> Department of Computer Science & Engineering
> IIT Kanpur
> http://home.iitk.ac.in/~kshitizg
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