A warning: R:\SDKs\llvm\trunk\include\llvm/Analysis/LibCallSemantics.h(63) : warning C4099: 'llvm::LibCallFunctionInfo' : type name first seen using 'class' now seen using 'struct' R:\SDKs\llvm\trunk\include\llvm/Analysis/LibCallAliasAnalysis.h(22) : see declaration of 'llvm::LibCallFunctionInfo' The problem line appears to be in file LibCallAliasAnalysis.h on line 21: class LibCallFunctionInfo; LibCallFunctionInfo is actually a struct, not a class, thus the forward declaration should be: struct LibCallFunctionInfo;