[PATCH] DebugInfo: SROA on references should result in undef dbg.values

[David Blaikie]

>>! In D3714#11, @echristo wrote:
> The debug info side of things sounds ok for now, it might be nice to figure out some way to represent the value in the future with the type.

Yeah - I believe that's in the territory of DWARF extensions/improvements. For now, so far as I understand DWARF, you can only describe the value of the variable (a pointer in this case, and something we don't have anymore - we'd need the opposite of DW_OP_deref (DW_OP_addr_of?)). Not sure if this overlaps with the broader problem of things like Argument Promotion, but I think it does.

Prior to that, though, we may need a better structured representation of addresses - I know, for example, that a screwed up when fixing the pass-by-non-trivial-copy (fixing the bug where we described those parameters as references instead of values) - by tagging the DIVariable itself with the "indirect" flag. That's no good in cases like this - we'll need to be able to add/remove such description on a per-variable-instance basis, so it should go in the dbg.value/declare/whatnot in a way that things like ArgPromo can see it and remove it if they get fancy (hey, we inlined your copy ctor/dtor and found nothing interesting, so we promoted your pass-by-non-trivial-copy to a trivial copy, but we can still describe the location of that variable, etc... - we still have the issue with "how does the debugger call this function now that it doesn't match the ABI" which we've also bantered about a bit)

http://reviews.llvm.org/D3714