A consequence of JDK-8266329 is that -Xcomp on libgraal does a lot more class loading and therefore a lot more compilation during VM startup than C2.

The reason is that EnableJVMCI automatically adds the jdk.internal.vm.ci module which disables the CDS archived full module graph (FMG). Without FMG, a lot of core JDK classes must be loaded instead being read from the archive.

In the context of libgraal, there's never a need to load jdk.internal.vm.ci - it is already AOT compiled into libgraal. In local measurements on an empty main program with -Xcomp and a fastdebug build of libgraal, avoiding loading of jdk.internal.vm.ci and thus being able to use the FMG reduces execution time from 38 secs to 9 secs.