About writing an alias analysis pass for LLVM 3.1


I am now trying to write an alias analysis pass for LLVM 3.1. The pass is compiled into a .so library. When I loaded it into opt to perform evaluation with command:

opt -load my-so-lib -aa-eval foo.bc

the following errors occurred:

opt: raw_ostream.cpp:261: void llvm::raw_ostream::flush_nonempty(): Assertion OutBufCur > OutBufStart && “Invalid call to flush_nonempty.”’ failed.`

As stated in the documentation I found on LLVM official website, an alias analysis pass should subclass both Pass and AliasAnalysis class. I used GDB for some debugging, and found why the error emerged.

By MyAA note the pass class written by me, and by obj note the instance of MyAA. In the crash scene, When LLVM was trying to call obj.alias, a virtual function of class llvm::AliasAnalysis, it actually called obj.print, a virtual function of llvm::Pass, because of the confusion of two virtual function tables. It seems that LLVM assesses obj via a AliasAnalysis* pointer without performing static_cast. However, I have no idea why this happens. I guess it is because I registered the Pass in a wrong way, but still don’t know to fix it.

Anyone can help me? I am not a C++ or LLVM expert, so I got really stranded.

Thank you in advance.

Pei Wang


Does your pass use multiple inheritance? Sounds like your problem is
that you need to define getAdjustedAnalysisPointer, see:


An example implementation (very likely exactly what you want) is in


Hope this helps!


Hi Will,

That's exactly the solution. Thanks!