Accessing llvm.global.annotations.cpp

    if(GlobalVariable* GA = M.getGlobalVariable("llvm.global.annotations")) {
      // the first operand holds the metadata
      for (Value *AOp : GA->operands()) {
        // all metadata are stored in an array of struct of metadata
        if (ConstantArray *CA = dyn_cast<ConstantArray>(AOp)) {
          // so iterate over the operands
          for (Value *CAOp : CA->operands()) {
            // get the struct, which holds a pointer to the annotated function
            // as first field, and the annotation as second field
            if (ConstantStruct *CS = dyn_cast<ConstantStruct>(CAOp)) {
              if (CS->getNumOperands() >= 2) {
                Function* AnnotatedFunction = cast<Function>(CS->getOperand(0)->getOperand(0));
                // the second field is a pointer to a global constant Array that holds the string
                if (GlobalVariable *GAnn =
                    dyn_cast<GlobalVariable>(CS->getOperand(1)->getOperand(0))) {
                  if (ConstantDataArray *A =
                      dyn_cast<ConstantDataArray>(GAnn->getOperand(0))) {
                    // we have the annotation! Check it's an epona annotation and process
                    StringRef AS = A->getAsString();
                    if (AS.startswith(Marker)) {
                      FuncAnnotations[AnnotatedFunction].emplace_back(AS);
                    }
                  }
                }
              }
            }
          }
        }
      }
    }