After playing with @requires the following problems related vm flags have been discovered:

1) Work with optional flags having numeric values.

 @requires vm.opt.G1HeapRegionSize > 10m

jtreg -vmoptions:-XX:G1HeapRegionSize=1m A.java
Error. Error evaluating expression: invalid numeric value: 1m

jtreg -verbose A.java
Error. Error evaluating expression: invalid numeric value: null

 * @requires vm.opt.G1HeapRegionSize == null | vm.opt.G1HeapRegionSize > 10m
jtreg A.java
Error. Error evaluating expression: invalid numeric value: null

problems:
- no way to check if a flag is set
- -XX:abc=10m is not treated as 10 * 1024*1024

2) 'x == false' and 'x != true' are not the same

 * @requires vm.opt.UseG1GC != true
jtreg A.java
Test results: passed: 1


 * @requires vm.opt.UseG1GC == false
jtreg A.java
Test results: no tests selected

problem: confusing behavior