[PATCH] D76336: [DWARF] Emit DW_AT_call_pc for tail calls

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

>> @dblaikie wrote:
>> why is this only relevant in optimized builds?
> 
> I think the main benefit of the call-site information is using it together with call-site-parameters, used for computing the actual value of parameter, even the location of the parameter was not provided (optimized-out).

That presents some interestingly tricky challenges. We have -fstandalone-debug for if you are building one part of a program with debug info an others without - but there's nothing equivalent for if you're building part of a program optimized but other parts unoptimized. And this heuristic (only emit these attributes for optimized code) assumes the caller and callee are both equally optimized/similarly compiled - which isn't necessarily true.

> That improves debugging user experience when debugging optimized code. In addition, in the case of tail calls, the call_site debug info is used for printing artificial call frames for the tail calls (and tail calls are typical to optimized code?).

The tail call case is easier - since that's the caller-side. It'd probably be better to just emit that on any tail call, optimized or unoptimized code - I guess I mean, ideally the choice wouldn't be made at the frontend, but at the backend if the call ends up being a tail call.

(I'm thinking of LTO situations, attribute optnone, other things like that - the frontend doesn't really know if something is optimized or not & really you can't tell if a callee is optimized because it's in another translation unit)

But such is life/some of that has no obvious solution. Wonder what GCC does.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D76336/new/

https://reviews.llvm.org/D76336