And it's not just two engines, but four, with at least one of them using the amount of available executable memory to choose whether to switch between them.
I know WebKit has tons of tests, but there must be some truly hairy bugs in that code. Does anybody know how they exercise the various optimize/deoptimize steps?
One neat testing strategy is to artificially lower counter used to tier up. Instead of using 1000 for DFG and 100000 for FTL, use something like 10 for DFG and 100 for FTL. This will cause lots of opt/deopt stress and can discover correctness bugs which may hide in more normal executions.
I know WebKit has tons of tests, but there must be some truly hairy bugs in that code. Does anybody know how they exercise the various optimize/deoptimize steps?