On Tue, Jul 24, 2018 at 12:39 PM Jakub Jelinek <ja...@redhat.com> wrote: > > On Tue, Jul 24, 2018 at 12:29:37PM +0200, Tom de Vries wrote: > > > I wonder if it makes sense to disambiguate things from the gcc side > > > by generating an empty location description for known optimized out > > > values (the standard seems to explicitely call that out as a way to > > > say "optimized out"). > > You can't emit the empty location descriptions in the middle of other > expressions though,
True. We'd have to "fold" any expression dependend on the optimized out value to optimized out itself. > and if you have e.g. an expression that uses > DW_OP_GNU_variable_size only conditionally, even if you know that > the corresponding DIE doesn't have location, the containing DWARF expression > could still be well defined if the condition guarding the > DW_OP_GNU_variable_size isn't true. DW_OP_GNU_variable_value you mean. That's true. But I was talking about omitting DW_AT_upper_bound which would correspond to int[] vs. a empty location list DW_AT_upper_bound which would correspond to int[<something>]. ISTR we quite aggressively prune DW_OP_GNU_variable_values that we cannot resolve. > And, also, for DW_OP_GNU_variable_size DIE lookup should be performed, > say you have only a declaration in the TU, but definition somewhere else, > in that case the debugger should be using that other TU's definition > with hopefully location description. Or if there is a global variable > interposed by some other TU, again, DW_OP_GNU_variable_size should follow > to whatever variable wins. Not sure if that is how it behaves (well, gdb still doesn't support DW_OP_GNU_variable_value). Related is probably that I wanted to have debug info of VLAs in the abstract instance so we'd have a DW_OP_GNU_variable_value of a DIE in the abstract instance (with no location) and the concrete instance DIE of the refered to DIE would only be related to it via its DW_AT_abstract_origin attribute. Ideally that would just work but given lacking gdb support I couldn't figure that out and thus we re-emit the whole type in the concrete instances... If we sort that out we can drop all of the VLA type remapping during inlining / cloning I think given we have debug info for the abstract instance around. Richard. > > Jakub
