The current implementation of compile command has two types of options. Types pre-defined options like "compileonly" and the general 'option' type.

'option'-type are not defined, they can accidentally be used with the wrong value type, and the syntax is error prone.

By pre-defining all compile commands used and giving them types the parsing can be simplified, proper parsing errors can be given and and reasonable syntax can be used.

This:
-XX:CompileCommand=option,java/util/String.toString,int,RepeatCompilation,5

Is superseded by:
-XX:CompileCommand=RepeatCompilation,java/util/String.toString,5

Attention check: Did you spot the error in the old command?

In order not to break anything - the old syntax is kept for now. But even the old command format is improved with verification for the option name and the type of the value.