On Tue, Aug 20, 2019 at 03:42:53PM -0600, Jeff Law wrote: > > I have been thinking about Segher's suggestion on providing options to > > lift some of the limitations, for compiler testing. Unfortunately, many > > of the restrictions are deeply rooted in the design of the > > architecture... or the other way around. Finding sane ways to implement > > these extensions will be fun :) > Hell, it's a virtual architecture. I'd just make up new instructions > for the missing functionality, make them dependent on an flag. I think > the PRU is in a similar position and uses that approach. PTX might have > as well.
This approach works well for simulators for physical architectures, too. > > This may change at some point. There is much discussion among the > > kernel hackers in whether it is possible to allow bounded loops in a > > safe way. In that case, some of the restrictions may be lifted. > ACK. It's an interesting problem. Would it help if we could annotate > loops with bound information? Not sure how to preserve that from gimple > down to assembly, but it's worth pondering. You probably should have machine insns that iterate a loop some number of times given when you first start the loop (and cannot be changed later, except maybe exiting from the loop). Like "doloop" in GCC. Maybe only allow a constant number of times, if the verifier want to see that? The only thing the verifier should be concerned with is how long the code takes to run, or am I missing something? Segher
