Share classes specific code patched to OpenJDK usually have comments such as //IBM-shared_classes_misc which is going to be changed to //OpenJ9-shared_classes_misc as per ibmruntimes/openj9-openjdk-jdk11#113.
Unlike https://github.com/ibmruntimes/openj9-openjdk-jdk, https://github.com/ibmruntimes/openj9-openjdk-jdk12, and https://github.com/ibmruntimes/openj9-openjdk-jdk11, those share classes specific code within this repo doesn't have such comments which makes identifying those share classes code less straightforward.
FYI: @DanHeidinga @pshipton @hangshao0