Experimental, using non-existent DWARF support to use an expr for the
location involving an addr_index (to compute address + offset so
addresses can be reused in more places).
The global variable debug info had to be deferred until the end of the
module (so bss variables would all be emitted first - so their labels
would have the relevant section). Non-bss variables seemed to not have
their label assigned to a section even at the end of the module, so I
didn't know what to do there.
Also, the hashing code is broken - doesn't know how to hash these
expressions (& isn't hashing anything inside subprograms, which seems
problematic), so for test purposes this change just skips the hash
computation. (GCC's actually overly sensitive in its hash function, it
seems - I'm forgetting the specific case right now - anyway, we might
want to just use the frontend-known file hash and give up on optimistic
.dwo/.dwp reuse)
Given the ability provided by DWARFv5 rnglists to reuse addresses in the
address pool, it can be advantageous to object file size to use range
encodings even when the range could be described by a direct low/high
pc.
Add a flag to allow enabling this in DWARFv5 for the purpose of
experimentation/data gathering.
It might be that it makes sense to enable this functionality by default
for DWARFv5 + Split DWARF at least, where the tradeoff/desire to
optimize for .o file size is more explicit and .o bytes are higher
priority than .dwo bytes.