So to generalize. The following registers are available, under the following conditions:
* Registers R16-R31 are always available for the allocator. * Registers R0-R15 are available between sub calls. That is, for any symbol, whose life range does not cross a subroutine. (This implies that all registers are available if no subs are called.) Since we have no way to determine if a sub is using those or not, any sub call will be assumed to possibly use R0-R15. Furthermore, even though we know there are certain registers in that range, which are unused by the calling convention, we will still not use them through a sub call for security reasons. * [NEW] If register 15 or below is used, it should be cleared out, ZEROED, after it's last use and before the next sub call. This is for security reasons. Obviously, these registers will not be the first choice to use. * Availability of these registers is subject to the rules for using the Parrot opcode C<setp_ind Ix, Py>, which were (are being?) worked through by Leo. Other observations: * Leo introduced a flag on the symbol, to indicate if it's volatile or not. These will be eligible for R0-R15 (volitile registers?). * From new allocator bugs, and analysis, we've discovered that exceptions cause new control flow edges, not previously considerd. This case is being reworked by Leo? to provide missing CFG edges, through a minor change in the try block declaration. (thread "Continuations, basic blocks, loops and register allocation") * The case of continuations has not been solved with respect to register alloction. Leo's RESUMEABLE: label might provide help here. In any case, we can expect to see some additional edges being inserted though. (also thread "Continuations, basic blocks, loops and register allocation") Did I miss anything?
