[llvm-dev] LoopInfo Analysis Fails on Module Pass

[Michael Kruse via llvm-dev]

For the legacy pass manager, it is not intended to invoke passes for
inner structure units (here: LoopInfo is a FunctionPass) from larger
structure passes (here: ModulePass). However, there is an exception
for invoking FunctionPasses from ModulePasses call "on-the-fly" but
which keeps only the analysis of a single function active at a time.

In your case, the LoopInfoWrapper pass must have been registered
before it can be used. Call

  PassRegistry &Registry = *PassRegistry::getPassRegistry();
  initializeAnalysis(Registry);

to do so.

Michael

Am Di., 14. Sept. 2021 um 20:51 Uhr schrieb via llvm-dev
<llvm-dev at lists.llvm.org>:
>
>
> Hi,
>
> I am trying to obtain LoopInfo Analysis from a Module Pass. My code goes
> like:
>
>
>
>     void SomePass::someFunction (Module &M) {
>
>     for (auto &F : M) {
>
>            LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>(F).getLoopInfo();
> //doing this gives me error shown below
>
>            for (auto &B : F) {
>
>                        //some use of LI
>              }
>          }
>
>       }
>
>
>    The runtime error message that I am getting is:
>
>    opt: /usr/lib/llvm-10/include/llvm/PassAnalysisSupport.h:262: AnalysisType&
> llvm::Pass::getAnalysisID(llvm::AnalysisID, llvm::Function&) [with
> AnalysisType = llvm::LoopInfoWrapperPass; llvm::AnalysisID = const void*]:
> Assertion `ResultPass && "Unable to find requested analysis info"' failed.
>
>
>   I also have defined the analysis usage function as follows:
>
>       /*void getAnalysisUsage(AnalysisUsage &AU) const
>      {
>              //AU.setPreservesAll(); // I am actually instrumenting the IR, so
> I am not sure this is required. The error occurs regardless.
>              AU.addRequired<LoopInfoWrapperPass>();
>      }*/
>
>
>    Is there anything that I am missing here?
>
>
>    Thanks,
>    Bodhi
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