This patch makes InstrRefBasedLDV "safe" to work with DBG_VALUE_LISTs. It
doesn't actually interpret them, but it recognises that they specify
variable locations and avoids propagating false locations, which is better
than the current state. Observe the attached tes
* We avoid propagating DBG_VALUE_LISTs into successor blocks, as they're
not "currently" supported,
* We don't propagate other variable locations across DBG_VALUE_LISTs,
because we know that the variable location is terminated by the
DBG_VALUE_LIST.
Differential Revision: https://reviews.llvm.org/D108143
ce8254d096