The already-existing special case for conditionals on clock has been
remade as follows:
- now triggered for the last remaining edge trigger after all others
have been converted to async reset, not just when there is only one
sync rule in the first place
- does not require all contained assignments to be constant, as opposed
to a reset conditional — merely const-folds the condition
In addition, the code has been refactored a bit; as a bonus, the
priority order of async resets found is now preserved in resulting sync
rule ordering (though this is not yet respected by proc_dff).
Fixes#2656.
This can pave the way for further transformations by exposing
identities that were previously hidden in a process to any pass that
uses SigMap. Indeed, this commit removes some ad-hoc logic from
proc_init that appears to have been tailored to the output of
genrtlil in favor of using `SigMap.apply()`. (This removal is not
optional, as the ad-hoc logic cannot cope with the result of running
proc_prune; a similar issue was fixed in proc_arst.)
o Not all derived methods were marked 'override', but it is a great
feature of C++11 that we should make use of.
o While at it: touched header files got a -*- c++ -*- for emacs to
provide support for that language.
o use YS_OVERRIDE for all override keywords (though we should probably
use the plain keyword going forward now that C++11 is established)